Now that we have some more international members, I thought it might be an idea to raise this topic once again.

Any of you who have read through some of my earlier posts will know that I'm not a fan of the British-style ring circuit.

How does anyone else feel about it? It would be interesting to compare opinions from those who are used to working with it (U.K. members, of course!) with those who are only looking at it from a theoretical point of view.

Do you like the concept? Do those of you who have to work with rings in practice like them, or would you rather see Britain move back toward radial circuits?

Can you explain the exact concept of "ring and radial circuits"? I'm not sure if I understand what you mean.
Do the British have the cables running in tubes or are the just in the walls?

Belgian,
Ring circuits are used to supply 13A (BS1363) sockets & certain fixed appliances (up to 3Kw) via 13A fused connection units.
A ring circuit starts at a 30/32A MCB in the consumer unit, loops in & out of each socket / fused connection unit in the circuit & back to the same 30/32A MCB.
Minimum cable size is 2.5 sq mm Cu/PVC.
A ring circuit may supply an unlimited number of sockets, in a maximum floor area of 100 sq M, providing that the known or estimated load does not exceed the value of the MCB.

Radial socket circuits start at the MCB, loop in & out of each socket in the circuit & terminate at the furthest socket in the circuit. (The same as Belgian practice I assume.)
Radial circuits may also serve an unlimited number of sockets, in a given floor area, providing that the known or estimated load does not exceed the value of the MCB.
20A Radial:
Min. cable size = 2.5 sq mm Cu/PVC.
Max floor area served = 50 sq M.
30 or 32A Radial:
Min. cable size = 4 sq mm Cu/PVC.
Max floor area served = 75 sq M.

Most UK residential wiring is carried out in PVC insulated & PVC sheathed "twin & earth" cable, similar to US "Romex" cable.
The cable is usually run in building voids, under floors, above ceilings & within timber stud partitions without any conduit tubing.
When run under plaster in solid walls (frequently encountered in England!) it should be protected by capping or conduit. This conduit usually only runs from the socket up to the ceiling or down to the floor, depending on wiring & construction methods.
Rewiring or adding extra points at a later date can be a major pain in the a***!

I have a copy of Legrand's International Wiring Guide, which illustrates the basics of the 4 main wiring standards; US, UK, French & German.
I will attempt to e-mail it to Paul (hopefully sometime this week) for him to post, as I think it may help us understand each other's systems.

In Austria we use only radial circuits, usually 1.5 sq. mm fused 10/13 or sometimes 16A (different values for fuses/breakers), lights and sockets usually mixed. Walls are typically brick, directly plastered (We don't bother with horsehair, bonding agent,... and whatever I've heard about US plastering, our plaster is lime with sand and usually (not necessarily) cement, older plaster is just plain mud mixed with water, sandbox style) sometimes 2" or 3" gypsum mixed with lumps of steel dross (hope I got this right out of the dictionary, it's some remnant of the steel production), supplied in panels 30x60 cm for interior walls. Plaster and lathe was commonly used for ceilings, for finished attic walls and in rural wood structures, always with straw mats nailed onto the lathes for better keying. Wiring is run within the walls, either NM direct buried or THHN in PVC flex conduit. Junction boxes theoretically have to be located above each switch and receptacle (both to avoid too many bends with conduit, and to be able to guess where the wiring runs without having a map.) I hope I can find room wiring schematics and post them. Ceilings contain only the wires to the light fixtures. For adding outlets or anything else it's usually inavoidable to get a sledge hammer and a good chisel, or better a rotary drill hammer with a flat chisel bit. (Myself I use a Bosch hammer for roughly $159.90, 159.90 Euro, Hilti hammers are also very common).
Personally I prefer ripping up walls over fishing in cavity walls, you can see what you're doing. Wires within wall/ceiling vavities MUST be in conduit.
In the 1970ies and 80ies the use of drywall with standardized aluminium profile studs (Knauf has almost a monopoly on them, Rigips, a brand name, has become synonymous for plasterboard). These studs have KOs for conduit I think every 50 cm.
However, exterior walls are still typically brickwork.

You guys all have one thing in common: you have the wires in the walls. Here, the cables are often surface mounted. It's not very common on new buildings, but when cables are added or a building rewired all of the wiring end up on the surface of the wall. I suppose Swedish sparkies don't like fishing

Are the surface-mounted wires placed in raceways or are they just stapled directly to the wall? Doesn't that expose the wires to potential damage?

Here, when people do surface mount wiring, they either put individual wires in raceways or conduit attached to the wall.

Of course you've got the idiots who tack two-conductor lamp cord (usually #16) to the walls and run it to surface mount Bakelite outlets and those old-style round switches....

Conduit is used IN walls, not ON walls.

You see: cables are in danger when they are in the wall. Someone might put a nail in them, drill into them or something like that.

Surface mounted, they are perfectly safe. In fact, one of the popular cable types is only approved for visible surface mount. The reason for this is simple: to give the cable a nicer apperance they have cut down on the insulation and up until two years ago the metal shield was ungrounded. Then the European harmonization forced them to add a thin ground wire to the shield. You're not allowed to use it as equipment ground, it's only there to ground the shield. (The electric safety authorities ensure that it is safe to ground it: There is a thin layer of plastic around the shield which prevents anyone from touching it.)

The rest of the world seem to do everything backwards! I learn that Americans put the cable on the wall and then staple it. We do it the other way round: First hammer in the staples, then put the cable in the staples! (You use pliers to fold the staples around the cable)



[This message has been edited by C-H (edited 10-14-2002).]

>A ring circuit starts at a 30/32A MCB in the consumer unit, loops in & out of each socket / fused connection unit in the circuit & back to the same 30/32A MCB.
Minimum cable size is 2.5 sq mm Cu/PVC.

Why does it go back to the same 30/32A MCB? Is this yo have better ground-fault protection (since it's a TN system)? What type of curve do you have to use in breakers (B/C)?
The cable is 2.5mm2 and you use a 30/32A breaker? How is this wire protected for over Ampering?(sorry for my English)

>I have a copy of Legrand's International Wiring Guide, which illustrates the basics of the 4 main wiring standards; US, UK, French & German.

I would appreciate if you could email to me, too: elieserthegr8@hotmail.com

The idea is that, since you have two cables you can double the fuse. 16A coming from one side of the ring and 16A coming from the other.

Therefore 2.5mm2 is sufficient. If the load is not connected at the middle of the ring or if it is not evenly distributed along the ring, there will be an unbalance in the load: You might have 20A on one side and 12A on the other.

If for some reason the ring is broken or the load is connected very close to the breaker, there is nothing to protect the 2.5mm2 cable. It could carry the full 32A. Would you like to have a system like this? Personally, I find it scary.


I leave it to the Brits to answer this, but what do you use in Belgium? Please tell me you use type B for sockets! Do you use 20A or 16A for them, BTW?

>Is this yo have better ground-fault
>protection (since it's a TN system)?

This is in fact one of the advantages of the ring main. It offers a high integrity earth. If for some reason the earth wire comes loose or break along the way, there is backup wire on the other side. Therefore, the risk of finding yourself with a live socket without earth is minimal.

I really like the idea of a ring system, but I don't like overfusing it. Your opinions on a ring main with 20A fuses? It would allow long runs with 2.5 mm2 cable and offer high intergrity earth, without any risk of fire. This should be of special interest to Americans, since cuircuits in 120V wiring are limited by voltage drop much more often than our 230V ones. (Forget the NEC for a moment - think free! )

[This message has been edited by C-H (edited 10-14-2002).]

C-H, Thanks for your explanation.

>but what do you use in Belgium? Please tell me you use type B for sockets! Do you use 20A or 16A for them, BTW?

In belgium we have a TT system (in residential installations) and therefore use type C curve. We use the radial system (as you understood) and we use 2.5mm2 wire/cables with a max value if breaker being 20A. All sockets have to be with ground.

Even if you use a TT system, you must have something to protect the .75 mm2 lamp cords from short-circuit? (A 20A type C breaker will allow 100A current for several seconds. There won't be a trace left of the lamp cord by then...)

Some people might be wondering what TT and TN has to do with tripping curves of breakers. I'll attempt to explain it. In a TT system, there is no connection between earth and neutral. The Protective Earth is only connected to a ground rod. The resistance of this is too large to allow a short-circuit to ground. (With a 25 ohm ground rod, the current will only be 230V/25ohm = 10A.) Therefore, these systems always have an RCD (GFI), in the 100-500 mA range which cuts the power in case of a ground fault. Even if a time delay RCD is used for this, the response time is short enough to prevent the dangerously high voltage on metal objects connected to the protective earth present during a fault condition from killing someone.

In a TN system, there is a connection between neutral and earth. If there is short-circuit between live and earth, the current will be high enough to trip a breaker. For this reason, these systems don't need to be equipped with an over-all RCD. However, care must be taken that the fault current is high enough to trip the breaker within a short period of time (no more than 5 seconds). To check this, you do an earth loop resistance calculation and sometimes also test it once you have made the actual wiring. A fast breaker (type B) will allow a higher resistance than a slow-blow (type C), and hence longer runs.

If you can't get a low enough resistance, you need to install an RCD, just like in the TT system.


[This message has been edited by C-H (edited 10-14-2002).]

>Even if you use a TT system, you must have something to protect the .75 mm2 lamp cords from short-circuit? (A 20A type C breaker will allow 100A current for several seconds. There won't be a trace left of the lamp cord by then...)

I presume that by lamp cord you mean the cord which goes from the cieling to the lamp.
Are you so sure that a few seconds of 100A on a 0.75mm2 will make that there is no trace left of the lamp cord? Remember that the lamp cord is relatively short.
If the lamp cord does melt, then it will be at the connecting points (b/c of the higher resistance at the connections). Therefore, The idea of the breaker is to protect the wiring in the walls (b/c of it's unaccessibility and fire hazard), not the lamps and appliances, which can be easily accessed.

What curve do you use in Sweden? (It is Sweden, right?) What's your solution to protecting the lamp cords?

I think David has provided a good outlined of the ring circuit.

Yes, the ground wire run in a ring gives redundancy in that a single break will not leave any outlet without a protective ground connection.

The same ring configuration on the phase and neutral means that a single break on either of these also results in no outlet being left without power. That's when problems with overloaded cables can start. I encounter such breaks in ring continuity on a fairly regular basis.

In cases where I find that both phase and neutral have no ring continuity, it almost always turns out to be somebody's DIY attempt at adding outlets which has left the ring broken.

I should also add to David's explanation the fact that our Regs. allow a ring to have "spurs." A spur is a single cable feeding a single or duplex receptacle which is connected to the ring at an outlet or junction box. The spur cable is also 2.5 sq. mm.

Although the IEE considers it unlikely to happen, it would be possible to connect two 3kW loads to a double socket and overload the spur cable.

Some months ago, we also discussed the exact distribution of current around a ring. The fact is that the ring is not completely foolproof. Given heavy loads connected close to one end of a long ring, it is still possible to exceed the cable rating on the short leg.

For some circuits BS7671 requires a disconnect time of under 0.4 sec., although 5 seconds is acceptable for lighting circuits, fixed appliances, etc.

Re the breakers, we generally use type B in all residential applications.

We used to use metal cable clips. These were nailed to the surface first, then the cable laid in and the strip bent around the cable and back on itself to secure it.

These days, the plastic saddle with a single nail driven on one side of it is standard.

Paul,
I'm in total agreement with what you say regarding ring continuity.
Breaks are usually as a result of botched DIY, growl! (I'm on the soap box again!)

There are times when I wish we could go back to radial circuits, but these are only when I am pulling my hair out attempting to locate a break in continuity, normally caused by the above.

I have to say that generally I like ring circuits for a number of reasons:
1) Permits relatively long cable runs, with limited voltage drop & low earth loop impedance (TN-S & TNC-S).
2) High integrity earthing, required to comply with section 607 of BS 7671.
3) Providing it is correctly designed, it allows a lot of sockets to be installed on a circuit with little chance of over-loading.(Kitchens excepted.)
4) In the event of a cable fault, you can disconnect the faulty section & temporarily restore power until a permanent repair / replacement can be made. Obviously precautions would have to be taken to prevent over-loading.

I was grateful of #4 above when I was called out this morning.
A ring main serving bedroom sockets in a nursing home went faulty, tripping the 32A MCB in the sub panel & also the 63A sub main MCB at the main panel.
I traced the fault to a live (phase)/ earth cable fault between the sub panel & 1st socket on the ring. Disconnecting this cable at the sub panel & 1st socket enabled me to re-energize the circuit, using a 16A MCB to prevent over-loading.
Next week I will go back & replace the faulty cable (after the joiner lifts chipboard flooring) & install a new split load sub panel incorperating RCD for the socket circuits.

I don't think unfused spurs should be allowed on a ring, they tend to be extended indiscriminately by those who know no better.

Breakers for ring circuit are normally "B curve" for residential, "C curve" for commercial / industrial. Nothing to prevent you installing "C curve" for residential, providing you can achieve the lower loop impedance values.
Generally socket circuits on TN systems have to disconnect within 0.4 second.
Socket circuits on TT systems must be protected by a 30mA RCD, also sockets which may reasonably be expected to supply equipment used outdoors on TN systems require 30mA RCD protection.

I have a policy of installing 30mA RCD protection to all residential socket circuits, in new work & when replacing an existing board (panel).

BTW what's "THHN in PVC flex conduit"?


[This message has been edited by David UK (edited 10-14-2002).]

>2) High integrity earthing, required to >comply with section 607 of BS 7671

How high is high ?
One break is relatively OK, you have a reduced capacity fault circuit, two breaks amd who knows ? (been there been very scared)
It's about time we had self diagnostic outlets - RCD outlets do it !

What price an LED

Testing is too much like an MOT - only valid on the day it's done.

Chris

Ah! You mean putting a green LED between live and earth to tell if the earth is OK? It sounds like a great idea. There really are some very simple things the lawmakers could do to improve safety.

Or from a socket to a lamp or any other small appliance (TV, radio, tape recorder)
Couldn't find a good word.


No, it was taking it too far. Evaporating the copper will take a huge amount of energy. (Copper melts at 1100°C, I think)

It is however easy to destroy the PVC insulation.

The maxium allowed operating temperatur for PVC is 70°C.

The maximum allowed short-circuit temperature of PVC is 160°C.

Thus there is 160-70 = 90°C of cable heat up available to handle a short-circuit.

How hot will a 0.75mm2 wire be if it is exposed to 100A for one second?

For copper, the specific heat is 0.39 kJ/(kg*K)

The density of copper is 8.9 x 10^3 kg/m3

The resistivity of copper is 1.7*10^-8 ohm*m2/m

I assume there is no change of state in the PVC and therefore neglect the heat absorbed by the insulation. (This can be justifed by doing the full calculations but I'll jump this part.)

I also assume the heat up is adiabatic, i.e. without any heat exchange to the surroundings.

energy = power x time
power = voltage x current
voltage = resistance x current
resistance = resistivity x length of wire/cross sectional area

Thus:
energy = resistivity x (length of wire/cross sectional area) x current^2 x time { * }

energy = increase in temperature x mass x specific heat

mass = density x length x cross sectional area

Thus:

increase in temperature = energy/(density x length x cross sectional area x specific heat) = {inserting * } = (resistivity x (length of wire/cross sectional area) x current^2 x time)/(density x length x cross sectional area x specific heat) = (resistivity x time x current^2)/(density x cross sectional area^2 x specific heat)

With numbers:

Temperature increase = 1.7x10^-8 x 1 x 100^2/(8.9x10^3 x (0.75x10^-6)^2 x 0.39x10^3) = 87 °C

We get an increase in temperature of 87°C, which is just within the 90°C limit. Hence, the cord survived. But had the breaker taken two seconds to trip it wouldn't.

>Remember that the lamp cord is
>relatively short.

I know you know the answer to this yourself. Why is a short cord better in a short-circuit situation? Is it:

1.) Because the cord will be cooler despite the same current going through it

or

2.) Because it has a lower resistance, increasing the current and thereby triggering a faster response from the breaker?

>If the lamp cord does melt, then it will be
>at the connecting points (b/c of the higher
>resistance at the connections).

Ah! I've never thought of this. It sounds reasonable.

>What curve do you use in Sweden?

Well - since 10A circuits are the norm (or at least used to be) type C breakers are common to prevent nuisance trips when you start motors (like the vaccum cleaner). D-I-Y:ers always use type C for everything. They would use type D if they could buy them... Electricans use what is deemed suitable for the circuit, hence often type B.

Most homes have cartridge fuses, and these are now slow-blow. You could buy both fast and slow fuses a few years ago, but since nobody bought the fast ones, they have now disappeared. (Ranger - what is the situation concerning Diazed fuses in Austria?)

Many fuses also feature the "infinte" trip curve. (Copper wire or similar wrapped around the fuse. Or a nail through the fuse) These are so very convenient - never any blown fuses. *sarcasm*

What kind of fuses are used in Belgium?

Sorry Paul - I'm ruining your thread!

C-H, Let me add another point which came to me overnight. About the lamp cord (or whatever appliance).

As aelectrician it's his duty to protect HIS wiring, not the wirings of the radio/lamp manufacturers. That is their duty.
On their behalf I can presume that they think this way:
Why would there be a 100A flowing through a 0.75mm2?
If there is a ground fault, then the RGI will trip in 0.6 seconds. If it's a short, then the breaker will trip even faster.

Thank you for all those calculations!

As to what we use in Belgium. Well we don't use fuses at all anymore. We use only breakers C curve (residential). Even the main one is a breaker. We do find still older installations with fuses, including the "infinite" type.

Paul, I'm sorry, too for ruining it.
I've had time to think abbout your ring circuits. My personal opinion is that it's a bad joke. What's the idea behind it? To save a bit of work or copper? Then why don't you branch it off a few more places (in midlle of the ring) to the 32A breaker? That way you could use 0.75mm2!
That is, of course, untill that one of them has a loose connection and the whole house is on fire. It's tippicaly British to think of something like that! This would never be allowed in France or Belgium.

[This message has been edited by Belgian (edited 10-15-2002).]

C-H & Belgian,

No problem on the diversion to cords and proper protection. One thing leads to another in these discussions, and they're often related somehow anyway.

I'm often amused by the instructions that come with appliances sold in the U.K. along the lines that the plug "MUST be fitted with a 3A fuse" (their emphasis). Yet the same appliance, fitted with the same 0.75 sq. mm cord is now likely to be sold right across Europe, where in most cases it will be connected to a circuit fused at 16 or even 20A.

By the way, although 0.75 sq. mm is the smallest size generally used on Continental cords, some small appliances sold specifically for the U.K. are fitted with 0.5 sq. mm (e.g. table lamps). That's when the protection of a 3A fuse in the plug is really needed.

I agree with David about the extensions to spurs on our ring circuits. (Another sidenote: Most laymen here call them a "ring main," although the correct term is "ring final circuit.")

I've seen extra spurs daisy-chained from an original spur far too often, sometimes three or four. They're often feeding outlets in adjacent rooms, and thus it's quite likely that somebody could plug two or more high-power devices in simultaneously.

I seem to be inserting "by the ways" a lot here, but another point is that the original ring specification set out by the IEE actually allowed a spur to feed two separate outlets, not the one which is permitted now. (I haven't got my old Regs. handy, but I have a feeling it may have changed only in the 15th Edition, 1981.)

David,
I carried out similar hacks before to get power restored. In fact in one house a while back tearing into the tiled walls to find the problem was going to cause so much damage that I converted a 30A kitchen ring into two 20A radial circuits permanently.(fortunately, the break came at a suitable place and there was a spare way in the panel!).

Hey, the less-gifted DIYers have enough trouble already!

Actually, any further cross-connections would be a violation of the Regs. There must be no more than two paths to any outlet on the circuit. (And it would be a nightmare trying to work out how much current would flow at any given point!).

THHN is a North American cable designation. It's basically just regular thermoplastic-insulated conductors. What's the standard temperature rating on these now guys? Is it still 75 deg. C or has it been increased to 95 deg. like NM-B?

>I'm often amused by the instructions that come with appliances sold in the U.K. along the lines that the plug "MUST be fitted with a 3A fuse" (their emphasis). Yet the same appliance, fitted with the same 0.75 sq. mm cord is now likely to be sold right across Europe, where in most cases it will be connected to a circuit fused at 16 or even 20A.

Paul,
According to my understanding, your 3A fuse is also for Ground-fault protection, whereas by us we have a GFI (we call it a differential) for that.

Okay, I KNEW I had forgotten something.
The oldest type of surface mount wiring are single cloth covered conductors wound around each other, mounted on glass or porcelaine insulators. This type of wiring has become really rare, maybe i'll retrofit such an installation and then post a pic of it.
In the 1950ies and maybe earlier they had brass clad wires (looked like conduit but was more a cable). The cloth seems to be just wrapped around the conductors, not woven, and the rubber is as brittle as can be. I usually tend to rip out every piece of that kind of wiring, or if unavoidable wrap the entire exposed length of conductor at devices with PVC tape. Same stuff with a softer metal sheathing and an additional cloth covering as a top layer was available for damp locations.
Nowadays either trunking (PVC or metal) is used or Romex is directly stapled to the walls. Very common during remodels/renovations! About my entire room except for the ceiling light and a single receptacle is wired like that. Our staples are what Paul described as "saddles" and have always been.
Everything is stapled like that, especially phone wiring. If the subscriber doesn't provide conduit when the phone line is installed you get the wires stapled to the wall.
A common way to add ground wires is to run 4 sq. mm ground wires from the panel along the baseboards to each receptacle.
I also know that there were special zip cord staples with a single nail going into the groove between the conductors.
In damp environments open conduit systems are used, i.e there are no bent pieces of conduit, in bends the Romex just hangs in mid-air. The conduit is intended mostly to keep the cable from making contact with the wall.
Concerning Diazed fuses: There were fast and slow ones, now they've been replaced by "general purpose". However, one of the scandinavian language (can't remember which one) clearly states "slow".
Hope I didn't forget anything.

Here in the U.S., as you all know we don't use ring circuits.

Please bear with me, I have never used a ring circuit. But this is where I first met Paul in a ring circuit thread on another forum.

Hi Paul, and all

Paul, I think I would have a problem with using spurs also. But if we were to do away with spurs and say bring the ends of the circuit back to two breakers on the same leg (say a waffer type) rated at the conductor amperage,(two 16 amp) instead of one breaker at twice the amperage, we would still arrive at the same capacity and reduce the chance of the conductor seeing more than its ampacity.

Of course here we can't parallel OCPD's, so I'm just rambling.

Roger



[This message has been edited by Roger (edited 10-15-2002).]

Yes, the fuse in plug, and those at the main distribution panel also provide ground-fault protection for TN-S and TN-C-S systems which don't incorporate a GFI.

Roger,
Yes, that was a while ago now, wasn't it? (By the way, I'm still reading the '02 NEC, but haven't had a lot of time recently!).

The two-breaker concept sounds interesting, but there's a problem (aside from being against our "Regs." that is).

If we used two breakers as you suggest, then we could only utilize the full 32A capacity of the ring and keep the current down to 16A on each breaker if the load were evenly distributed. Take an example: If the full load of 32A were connected at outlets approx. 25% of the distance around the ring, then by the resistance in the cables, one breaker would carry only 8A while the other would have to supply 24A.

Paul, I can relate to not having a lot of time on my hands lately too. I hope business and all things are going well.

I agree this would take more even load distributing along the circuit, but this same scenario happens on the single breaker circuit. Is this one of your concerns with using it?

In the two breaker circuit the conductors would be guarded at their value.

This would make the convenience of the circuit less desirable, but in my thinking safer.

Once again I confess my ignorance to this wiring method, but it's sure fun to talk about it.

Roger

You could use two 20A breakers. But if the neutral came loose one one side, you would find yourself with a 25% overload on one side. (Yes, I can show this mathematically. )


[This message has been edited by C-H (edited 10-17-2002).]

Roger,
Yes. The listed ampacity of our 2.5 sq. mm cable can be exceeded if a heavy enough load is connected close to one end of the ring. The absolute maximum for 2.5 cable is 27A "clipped direct" (i.e. surface run), but it can drop to 18.5A (buried in thermal insulation), or less if derating for bundling etc. is taken into account.

You might like to re-visit this thread from last year:
https://www.electrical-contractor.net/ubb/Forum9/HTML/000004.html



[This message has been edited by pauluk (edited 10-18-2002).]

I did a search on breaker types and came up with a document from Siemens. They have types, A, B, C, D.

The breakers all have the same thermal properties. The difference lies in the overcurrent required for the electromagnet to step in. It along with the intended use for the breaker type is listed below.

Type A: 2-3 times rating. To protect very sensitive circuits such as semiconductors.

Type B: 3-5 times rating. Designed to protect European residential circuits.

Type C: 5-10 times rating. For general device protection in control circuits etc.

Type D: 10-20 times rating. Designed as a supplementary protector of high inrush loads such as transformers and motors.

Comment: The type C 20A breakers Belgian use for the sockets will thus trip between 100-200A. The type B 32A breakers that Paul use for Ring mains will trip between 96-160A. Hence, there is less risk of fire and an appliance "blowing up" when it is connected to a British socket with live and neutral reversed, than when it is connected to a correctly wired Belgian socket.

>Comment: The type C 20A breakers Belgian use for the sockets will thus trip between 100-200A. The type B 32A breakers that Paul use for Ring mains will trip between 96-160A. Hence, there is less risk of fire and an appliance "blowing up" when it is connected to a British socket with live and neutral reversed, than when it is connected to a correctly wired Belgian socket.

You are forgetting that those breakers also have a thermal protection and therefore at 40A consumption on a 20A breaker type C will also trip after 25 seconds. A type B breaker 32A will never trip at 40A consumption.
Here is a link to the graphic display of the differences between B and C curves: http://194.2.245.4/pdf/fr/cat/BTKP380.pdf
(sorry that it's in french).

Here in Austria B types are used for residential and C types are used for workshop ect equipment with motors, causing a high startup surge. I was told at Baumax (like Home Depot) that they're the equivalent to quick and slow diazed fuses.

The thermal characteristics of the C/B with a moderate overload, rather than a drastic short circuit, could certainly make all the difference. While thinking of this, keep in mind also my comments above about some appliances in the U.K. having 0.5 sq mm. cords as well.

As David has pointed out, there is nothing to stop us using type-C breakers in residential applications, so long as the appropriate disconnect times can be achieved. Back when I was a kid in the early 1970s, my father rewired a 1930's house using the Crabtree C50 range C/Bs (I'll leave it your imagination to work out just how he happened to be using commercial-spec breakers! ).

That was on an old urban TN-S supply with a solid ground path on the armor of the cable, and thus a very low loop impedance. (It was also before the 5 sec. & 0.4 sec. disconnect times were part of the Regs., but I'm sure it would have satisfied those requirements anyway.)

I wouldn't mind betting that at the time, it was probably the only house in the street to have any sort of breakers rather than the rewireable fuses which were the most common form of protection in the early 70s.



[This message has been edited by pauluk (edited 10-20-2002).]

Looking back through this thread, I'd like to pull out one of David's point for the ring circuit:

The correctly designed aspect is something which I feel is often overlooked, and as noted, this certainly applies to kitchen areas.

Many people latch on the "one ring for 100 sq. meters" part of the Regs., and then just blindly follow that without allowing for the anticipated load which should also figure into the design.

U.K. members will bear me out on this: How many times do you see a two-ring house with one ring for each floor? The upper-floor ring is seldom loaded to more than a very small fraction of its capacity, especially now that central heating is widespread and thus the need even for portable heaters in bedrooms has diminished.

Then you look at the ground-floor ring and find it feeding a washing machine, a clothes dryer, and a dishwasher, as well as all the kitchen outlets.

The washing machine and dishwasher heating elements are usually 3kW, although admittedly they wouldn't be considered a continuous load. But the dryer element could easily be running for two hours at a stretch.

The countertop receptacles will likely be used for toasters, microwave ovens, and all the other high-power kitchen gadgets, including in most British homes the ubiquitous electric kettle (another 2 to 3kW).

These days, people do expect to be able to run everything at once. The one-ring-per-floor arrangement was fine years ago when the average British home didn't have the high power consumption found in a modern kitchen. But I think it's time the Regs. were amended to make allowance for increased kitchen loads and that designers make a better job of distributing the load between circuits.

I concede that there is a tendency now to specify a separate kitchen ring circuit, but to my way of thinking, that achieves very little. If somebody installs a separate ring for the kitchen area, we still have all the major appliances on the one ring while the other two rings are feeding a TV and an electric blanket.

Better yet, I'd like to see separate circuits specified (NEC-style) for washers, dishwashers and, especially, tumble dryers.

P.S. I'm using the terms ground floor and upper floor here to avoid the possible confusion over what constitutes the first, second floors, etc.

For those international members who aren't aware of the differences, allow me a slight detour to explain:

In the U.S.A. first floor means the ground floor. The level directly above it is the second floor.

In Britain, first floor means the first level ABOVE the ground floor, i.e. U.K. 1st floor = U.S. 2nd floor.

So much for English being a universal language!


[This message has been edited by pauluk (edited 10-20-2002).]

Quite right! This is why the 2.5 mm2 cables in ring mains run risk of overheat and fire. With radial circuits, this risk is neglible.

But, to an appliance cord, the thermal part of the breaker means little. If you put a 0.75 mm2 cord at 40A for 25 seconds, it will get very, very hot. (BTW. From the graphs you submitted, I get the "Must break" curve to be 200 seconds at 2 times the rating.)

You have pointed out that the thermal part is the same for both type B and C. Hence, there is no difference in current carrying capacity between the breaker, unless the current is 3 times the breakers rating. What is the purpose of using type C in a residential environment? You won't get more power out, except in a short-circuit situation.

>What is the purpose of using type C in a residential environment? You won't get more power out, except in a short-circuit situation.

Maybe because that with type C, bigger motors can start without making it trip or maybe because it's cheaper.

The way that we look at it, is that we use type B only in TN systems (here it's only in industrial installations) to protect for ground-fault problems.

>Maybe because that with type C, bigger
>motors can start without making it trip

Yep. For this reason 10A type B are quite useless as the inrush current of some vaccum cleaners can trip it. Also, for those big blue and red (IEC 309) sockets, type C is an obvious choice, as you can expect them to be used with large motors.

But here large single-phase motors are rarely used in places like living rooms and kitchens. If you need something like a five horse power motor, you'll probably put it in the garage connected to a big red 3-phase socket.

> Also, for those big blue and red (IEC 309) sockets, type C is an obvious choice, as you can expect them to be used with large motors.

What do you mean by big blue and red (IEC 309) sockets?

He's referring to the blue-grey (single phase) and red-grey connectors (the large ones for 3ph)
Don't you use them in Belgium? I've seen them all across Europe.

Also known as CEE 17

Thank for your clear information. Yes, we have them in belgium, too. http://www.gepowercontrols.com/47/72/78/10037/index.html#23240


[This message has been edited by Belgian (edited 10-23-2002).]

Belgian: When did you stop installing ungrounded sockets in Belgium?

Belgian and Ranger:
What do you do if you have to replace a broken ungrounded socket? Are ungrounded sockets available as replacements or do you simply put a grounded socket without ground wire?

The IEC309/CEE17 range are also recognized and used in the U.K., where we also know them under the designation BS4343.

As in most of Europe, the blue 2P+E (2-pole & earth) and red 4P+E are the most common, although the yellow 2P+E types are also used here on building sites where Health & Safety Regulations require portable tools to be 110V types. The low-voltage white and violet types are also found in some industrial locations.

The blue types for 1-ph 240V are almost universal now for RV and campsite hook-ups, in contrast with some parts of the Continent where Schuko or French-style outlets are common.


[This message has been edited by pauluk (edited 10-23-2002).]

We still use Ring circuits here, albeit for use in Caravan Parks, over large areas like we have here, the circuit is run in either
4mm Single Phase or 2.5mm2 Three Phase, spread equally over the number of points on the circuit.
These Ring circuits are fed via a Selective type RCD(100mA), with 30mA Personal protection RCD's at each Trailer Park point.
Standard over here is the use of CEE 17(Blue), for connection of Caravans.
All of the wiring is run in Neutral-Screened
cable, buried direct.
Also, the minimum length for a Caravan lead is 10 metres, with no joins.

There are 2 options for replacing a broken ungrounded socket: Pull a ground wire from the panel, along the baseboard and convert to Schuko, or find an old ungrounded receptacle you've taken out somewhere else before, install it and have the customer sign a paper stating you just replaced an existing outlet and didn't install anything new. Until 1998 it was also legal to put in a main GFI and use Schuko receptacles without ground, but this has been outlawed in this major code change.

In France you can still get two-pin ungrounded receptacles. I guess they're for replacement-use only, just like the American ones.

I saw them for sale at Castorama's website (which is owned by the same company as the British B&Q). This is sort of like Home Depot or Lowe's type stores here in the USA.

Ranger, if I lived in Austria and was working as your asisstant I could always volunteer to go to France and pick some up...hehehehehe.

Here is the link to one of these things at Castorama's website:
http://www.castorama.fr/boutique/sku/sku.jhtml?elementId=Casto832752&productId=CastoEL0301

Thanks Sven!

Castorama also has something else that I have been thinking of asking about, namely single width, double pole circuit breakers.

Look e.g. at this:
http://www.castorama.fr/boutique/sku/sku.jhtml?elementId=Casto824440&productId=CastoEL0205

Does anybody know if these work with busbars? Or if they exist in a 4 pole version?

Wow! Gotta get some of these receptacles if I ever come to France!
Pitifully our School trip scheduled last year was cancelled because of a teacher's strike.
They're the only 16A rated ungrounded receptacles I've ever seen! Our old ones were all 6 or 10A.

Ha!Our ungrounded plugs and sockets are rated 16A.

> Belgian: When did you stop installing ungrounded sockets in Belgium?
I think it was in 1981 when there were major changes done in our code. Our code is called A.R.E.I. It stands for Algemeen Reglementatie van Electrische Installaties.

What do you do if you have to replace a broken ungrounded socket? Are ungrounded sockets available as replacements or do you simply put a grounded socket without ground wire?
Our code says that you are aloud to use and repair ungrounded sockets from older installations and therefore we can still buy them. It is also written thet it's a breach of the code if you replace a old ungrounded socket with a grounded one without pulling a ground wire.


>Castorama also has something else that I have been thinking of asking about, namely single width, double pole circuit breakers....Does anybody know if these work with busbars? Or if they exist in a 4 pole version?

They are made by Legrand. We use them here when we need to add breakers in a "box" and there's no more space. Otherwise I don't find them good to work with, since the screws are very small and therefore can cause loose contacts.
There are special busbars for these models.
You mean single width 4 pole? No, it doesn't exist yet.


[This message has been edited by Belgian (edited 10-24-2002).]

That means you were way head of us. BTW. The title sounds like Flemish?


Same as here, then. What do you do if you add an extra socket in a room with old ungrounded cables?


Ah. It seemed like the only type Castorama had. I can imagine that they are not as good as ordinary breakers.

>There are special busbars for these models.

They must be pretty small?

>You mean single width 4 pole? No, it doesn't exist yet.

Single width 4 pole? Now, that'll be something! I meant double width 4 pole, but expressed myself poorly. (I doubt anyone could figure out what I meant...)

BTW. The socket you have in your post looks like it has a recessed engagement face? I'm I right? (Ours look just the same!)

[This message has been edited by C-H (edited 10-24-2002).]

Yes, the title is flemish. We also have the french version (title).
>What do you do if you add an extra socket in a room with old ungrounded cables?
The only solution then is to pull a ground wire. By you?
>It seemed like the only type Castorama had. I can imagine that they are not as good as ordinary breakers.
It IS the only make which makes them. No, they're not as good as the ordinary ones.
>They must be pretty small? Yes
>I meant double width 4 pole, but expressed myself poorly. No, they dont exist yet in double width 4 pole. It is a very recent product.
>The socket you have in your post looks like it has a recessed engagement face? I'm I right? (Ours look just the same!)
Yes, ours is also recessed.
The ones with ground pin; we have 2 models one half recessed and one full recessed.

>The only solution then is to pull a ground wire. By you?

Put an ungrounded socket, unless you are going to do major changes to the wiring. (I don't know where the line is drawn really.)

>Yes, ours is also recessed. The ones with ground pin;
>we have 2 models one half recessed and one full recessed.

Ok, I can see the difference. Why are there two types? Full recessed in wet areas? Does the ground pin protrude beyond the socket in the half recessed version?

>...unless you are going to do major changes to the wiring. (I don't know where the line is drawn really.)

By us it's the same law, but I would consider this a major change.
>Why are there two types?
Half recessed for places where you don't have enough space behind the socket e.g. to make more connections behind a socket.
>Does the ground pin protrude beyond the socket in the half recessed version?
Yes, but it has a "ring" which protrudes around the plug to protect the pin.

Paul,
With your disdain for a Ring Circuit, have you actually had a problem with a broken Neutral conductor, where this would cause an over-current in the remaining part of the circuit?.
Can a Ring Circuit be protected by an RCD, under your Regulations?.
Is the UK, coming into line, more with international(EU), hence the change in Regs
between the UK and the EU.

Yes, I've seen a broken neutral on a ring frequently. A broken phase conductor also results in the same problem. I've also found "rings" with a break on all conductors, usually the result of a bodged DIY extension.

Rings most certainly can be protected by an RCD; indeed in some cases they would be required to have such protection (e.g. a house using TT grounding where there is a main RCD/GFI).

There has been a gradual move toward Britain adopting common standards with Europe over the last couple of decades (and in a few cases before that. e.g. adoption of the common brown-blue-green/yellow flex colors and metric size cables in 1970). Circuit breakers which were once rated 5, 15, 30A for example are now often 6, 16, 32A.

There are still stumbling blocks which the various national bodies disagree on, and the basic circuit arrangement seems to be one. The IEE remains firmly attached to the ring circuit with fused plugs, a system not used anywhere else in Europe except Ireland, and even they seem to be adopting Continental standards now.

On the Ireland thing:

I've been in contact with an Irishman and according to him the BS 1363 is and remains the only socket in use in Ireland. However, the Irish system was originally built by German companies, and thus the German voltages (220/380), fuses (Diazed, Neozed) and the Schuko plug found their way to Ireland. The Schuko was discontinued when the BS 1363 was introduced.

I can see two possible explanations for the reports of Schukos or French sockets in Ireland. a) Someone has found an really old socket. b) Someone has for some reason installed them, e.g. an hotel as a service for European guests.

BTW. An interesting topic popped up at uk.d-i-y: Ring mains are now required to be designed in such a way that the load on each leg does not exceed 20A.

Thanks for that C-H. It certainly sounds a plausible explanation. I don't suppose you happened to find out exactly when the BS1363 plug was introduced as an official Irish standard?

Designing the ring so that the current doesn't exceed 20A on any part would require a certain minimum length of cable from distribution panel to the first socket, worked out as a percentage of the overall ring length.

>I don't suppose you happened to find out
>exactly when the BS1363 plug was introduced
>as an official Irish standard?

No, sorry!

>Designing the ring so that the current
>doesn't exceed 20A on any part would
>require a certain minimum length of cable
>from distribution panel to the first
>socket, worked out as a percentage of the
>overall ring length.

You can do the calculations, but someone had calculated that you "loose" 16% at the start and just as much at the end of the ring, making one third of the ring "passive".

C-H & Paul
The new ring main design rule in BS7671: 2001, Amendment No.1, February 2002, ammends Reg 433-02-04 to read:
"....Such ring final circuits are deemed to meet the requirements of Reg 433-02-01 if the current-carrying capacity (Iz) of the cable is not less than 20A, and if, under the intended conditions of use, the load current in any part of the ring is unlikely to exceed FOR LONG PERIODS the current-carrying capacity (Iz) of the cable."

These ammendments are available as a free download from the IEE website; www.iee.org.uk, there are also ammendments to the current ratings for BS 6004 flat twin & earth cables.

Hope this helps.

[This message has been edited by David UK (edited 11-04-2002).]

Thanks for the details. I hadn't seen that amendment yet.

I guess it leaves the door wide open for varying interpretations of what constitutes "intended use" and how one defines a "long period." Typical vague IEE wording.

I'd still rather just see rings abandoned entirely, although I know I'm in the minority in the UK for having that view.

Better late than never: Here is the definition of long period of time. One hour.

Article here

On the Irish BS1363 standard:

Schuko was used until the 1940s and quite possibily until the 1960s in some cases. As I'm sure you're aware the UK equivilant was a bit of a confusing mix of BS546 based plug and socket systems some of which were 2 pin some 3 pin and of at least 4 different incompatble sizes!

Siemens and AEG were the main contractors to the ESB in the early days (and still are!) so a lot of their standard components were used (Neozed/Diazed & Schuko)

Schuko sockets still survive in old installations, some of which are still in use and schuko plugs can still be purchased in hardware stores.

In many cases however schuko sockets that are still installed in skirting boards or woodwork etc are simply dead, they're usually very unobtrusive and recessed into the skirting and removing them would have been more difficult than just leaving them in place but disconnected.

BS546 was used in its 3-pin form (usually only the 15amp version) during the 1950s (immediately Post WWII). The 2amp version was adopted later for special purposes like wallswitch controlled plug-in lamps. The 15amp version is common place in stage lighting rigs (more recently being replaced with the more resiliant standard european industrial connectors)

BS1363 was the predominant standard from 1960 onwards and was given legal standing later with IS401 & IS401/A which are required to be complied with by legislation, very similar to the UK but still inforcing standards that may still exsist .. e.g. schuko plugs on sale are referenced to CEE 7 & appropriate DIN standards)

Pre-1960 it was very unsual to carry appliences from location to location so wheather Schuko or BS546 was used was really of no consequence.

Post 1960 portable appliences became much more common place, people moved radios from room to room.. vacuum cleaners etc were in much more widespread use.

BS1363 added a little bit of extra protection (was child proof & fused). Wheather the fuse was actually adding protection or not the public percieved it to be safer.

It also makes providing sockets outlets that can actually provide a full 13Amp supply should they need to much easier. Wheather they're wired on a ring or on a radial (which can be rated 20amps instead of 16). In many older European installations bedroom sockets were often unsuitable for large loads as more outlets were carried on 1 16amp or 10amp radial (often only accepting narrower pin plugs) or in the old British system were often the physically smaller 2 or 5amp BS546 sockets to prevent large loads from being connected.

BS1363 & the ring circuit / heavier radials meant that portable heaters etc could be used much more effectively at any location in the house without over-loading the system.

As time has gone on the ring circuitry has also meant that generally the number of outlets per room in a UK/Irish house is much higher making them much more suitable for modern living.

Irish electricians tended to have frowned upon very large rings however and they're not quite as common as they are in the UK.

They use the same rating for the cable but tend to be much more conservative with the fusing arrangements sometimes opting for 20amp breakers rather than 32 and using less sockets per ring or using radials.

Generally an irish consumer unit will generally have at least 2 rows of breakers or diazed/neozed fuses (were un use until the mid 1980s, Neozed is still acceptable but considered old-fashioned and impractacal for the consumer.. a switch is easier to reset!).
RCD has been obligatory since 1980 and we require a double pole isolator switch (now on the bottom of the meter) and main fuse (typically 63amps) installed on the consumer unit before the RCD. This is to protect the consumer unit itself from catching fire in a serious overload situation.

The power company also has a sealed fuse before the meter. This is usually 63/80/100 amps and unless someone shorts the two lines coming into the meter itself its only purpose is to disconnect the entire supply.

[This message has been edited by djk (edited 05-05-2003).]

That makes for interesting reading, but just goes to highlight the concerns that have been expressed here at ECN about the ring -- That it is not foolproof and without very careful planning it is quite possible to overload the cables even without faults, such as a broken phase or neutral.

I note the document mentions the committees' desire to retain the U.K. ring circuit. Thinking of another thread, I don't doubt that it's same bunch who want to adopt the CENELEC-type brown/black/gray phase colors!

Allow me to quote myself:
Six months on from that comment, but I stand by it.

And whether the present committees want to retain the ring or not, if we ever do get a Europe-wide standard for wiring I can't see the British ring being a part of it.

Paul,
I reckon you'd have your work cut out for you getting a prevalent system like that banned wouldn't you?.
I mean it's everywhere in the UK, isn't it?.
Are you proposing to use a Radial system instead?.
How would wiring a house (with say 4 points on each floor) compare price-wise, between the two systems?.

Yes, the ring circuit is found in practically every house in Britain. Even though the ring has been in use over 50 years now, the IEE Regs. have always kept radial circuits in as alternative arrangements, although the allowable number of outlets, floor area served per circuit etc. have changed regularly.

I haven't sat down and worked out the price difference, but as far as new construction is concerned, I don't think it would make much difference. 2.5mm twin-&-earth cable runs about £15 per 100m drum, typical domestic type-B MCBs about £4 to £5 each. Extra labor is just going to be pulling a few extra cable runs, which on a new building is easy. Compared to the overall costs of £2000 upward, any extra cost would be negligible.

Paul,
When you think about it,
Radial circuits would be easier to install than Rings.
I realise that a lot your houses in the UK are two-storey, but dropping a single wire down a wall, has to be easier than tearing up floorboards to get to ring cables.
What are your thoughts?.

I promised I would not comment any further on this topic, but here goes.
It would not really be "easier" to wire a house with the radial system. You won't have fewer floorboards to lift, & you still have 2 cables at each point except the final one.
I have installed both systems, the only difference would be that in radial you do not have to return to the consumer unit from the final point.
Utilising the radial system would result in extra socket circuits being required in the average home, and consequently a larger distribution board with more mcb's.
Bottom line is it would be more expensive, but not a lot more, I've never sat down & worked it out.
It is quite acceptable under UK regs to use radial socket circuits, I often do, when installing a limited number of sockets in a location remote from the consumer unit.

I think ultimately the ring main will be abandoned in the UK, EU harmonization will ensure that. As long as what replaces it is a better, safer system, then that's OK.
Until then British sparkies will continue to favour the ring main.

I have to comment on David and Trumpy:

The radial circuit doesn't need two cables at each socket. In fact, this may be frown upon by some constructors. In modern offices, flexibility is very important. The higher rent per area unit compared to older offices is compensated for by more efficient use of the area. (Or at least they try to)

This means that walls come up and go down as the company reorganises. Only the ceiling, floor and structural walls (don't know what to call the walls you can't remove) remain fixed. Obviously, cables run from socket to socket aren't suitable in removable walls.

Ok, you could do a ring in the ceiling and spur down, but a radial layout seems simpler.

C-H,
No disrespect mate, we were referring to residential construction.
Also modern installation practices in the UK & NZ? prefer loop in wiring methods, ie. joints made at accessories, avoiding the use of joint boxes.
Installing joint boxes adds to the time taken & puts another weak spot in the system.

Stuctured office cabling systems are often based on radials for that reason.

I can't see the huge advantage of ring circuits. There are some minor advantages in terms of saving cable but in a typical house, at least here in Ireland, rings can be very difficult to install. Solid interior walls are common (even in new buildings) as are concrete or even stone floors etc. So the usual approach is to take radials up to the attic from the consumer unit and feed them back down into the rooms through conduits burried in plasterwork or through wall cavities. On the ground floor where there is a suspended wooden floor (most houses) it's easier to run cables down from the consumer unit as radials and out to points taking an under-floor route. If there's a concrete floor they go into the ceiling.

There are a lot of advantages to a modern radial system too:

1) Easier trouble shooting. If something does go wrong you can trace faults by a simple process of elimination.
2) Adding extra circuits tends to be easier as the Comsumer Unit (Fuseboard) tends to be bigger and more flexible.
3) Circuits likely to cause a trip more frequently are on their own MCBs.. e.g. the kitchen, utlility room etc.. so there's less chance of loosing power in your office when the kettle short circuits! (Unless there's only one RCD and its a ground fault)


Rings generally are only easier if wiring can be run room to room horizontally behind walls. Having each socket hooking into a ring in the ceiling / floor doesn't really present any great advantage.

In any western european country the cost of labour is by far the biggest part of the cost of an electrical installation. Cable and circuit breakers are relatively cheap.

What's the cost of a MCB in the UK?
or cable per meter?

Decorative fittings tend to whack up the price too...

I just fail to see the huge advantage of using rings.. they seem unnecessarily complicated.

[This message has been edited by djk (edited 05-10-2003).]

DJK,

Re the cost of cable and MCBs, from my last post above:
If we look at the extra cost of a larger panel (consumer unit), it adds very little. For example, in my usual supplier's current catalog a Wylex insulated NH range 100A panel is £16.29 for the 5-way version and £24.69 for the 14-way (plus VAT). MCBs for this particular panel are £4.59 each, or down to £3.79 each in larger quantities. As you mentioned, compared to the other costs involved in a new installation, the possible extra cost of wiring with radial circuits is small.

My absolute favourite is the good old Austrian/German radial layout, also used in Spain and many other countries.



Troubleshooting can't be easier, even if you have no idea where which wire runs you can guess easily. For example, if you have a receptacle and there's no junction box directly above you start looking to the left and to the right. If you find a box for example a box to the left with 2 or 3 wires leaving to the right you can be pretty sure these are the wires feeding the receptacle. And in most cases you have only one set of wires at each outlet/switch. I do almost all my new wiring this way. Only in severe emergencies I run wires down to the floor and around the walls 30cm above the floor. (precisely this happened once in my life, since there were windows on both sides of the room, and I'd have had to go up very close to the ceiling to pass above the windows, so I decided to go beneath.)

Ranger,
What??.
We don't even use the junction box anymore in lighting circuits, unless its really necessary(alterations, etc).
All our joins are done at switches and light-fittings, although downlights make it harder, as they never have a loop terminal.

Ugly!
Starts to come up with new construction here too, but all retrofitting is done as I described. Switch boxes aren'T too big, I hate connections inside them, it makes almost impossible to get the device in. only junction boxes for me, the larger the better! Light fixtures, especially the very common pendants don't have any wiring space, only a strip connector covered by a plastic cup turned upside down. Making joints up there would mean to have a bunch of wires and conduits sticking out of a hole in the ceiling and you have to put lots of strip connectors into the "yoghurt can". New construction often puts 1 large junction box per room above a trap door in the drywall. But round and square junction boxes (from 10x10 cm up, I've seen 30x30 cm ones) are still widely used.

Hi I am currently in Australia but have worked on ring circuits in the UK personally I do not have a problem with ring or radial the debate has been around since Noah wired his boat shed. With regard to the current demand, that is covered in domestic situations by diversity or maximum demand. I do not know of too many houses where appliances in general use draw 20A continuous anyway. The only real problem I have had with rings was where a house I worked on had the ring connected to two individual fuses (yikes lucky I checked the supply before working on it)and they were 30A each! thats all folks! love the forum.
Steve.

PAUL UK


I think ring main circuits are not a bad way to install your power points, only there is possible downfalls to the system!One regulation i do think they should take a step back on is to increase the amount of spurs off any one socket to maybe two, taken into account the area it is situated this would save unnessarcery joints while exstending the ring.

I often wounder what would happen if a ring circuit was serving close to its carring capacity, and there was to be a break in the ring! Worse still the break could be a loose connection in the circuit breaker device, meaning your 100m2 floor area ring has now become a radial with a cable current carring capacity of around 23 amps (if buried in a wall) with a 32 amp rating on your protection device!!

Just a thought thats all.

I'm sure it wouldn't be altogether impossible to come up with a MCB or similar unit that could check the integrity of a ring and cut the power if it was not intact.

It could be done electronically by simply sending either a continious or intermittent signal down one side of the ring and if it doesn't come back on the otherside trip the MCB. Similar technologies exsist for controlling lamps etc remotely via piggybacking signaling onto the power system of a house.

Generally, unlike radial installations there are only 2 or 3 rings. So it wouldn't be economically prohibitive. They wouldn't necessarily have to be on the fuse board either. You could wire them in after it across the 2 X L and 2 X N of the ring (perhaps the earth integrity could be tested too).

Such a system could be made to fit into a standard DIN rail consumer unit.. even if it occupied a bit more space than a MCB..

It would be a pricy sollution but then again some people considered RCDs excessively pricy and unnecessary for years. If it prevented house fires it might be worth it.

Then again how many broken rings have caused house fires?

DIY jobs on radial circuitry is often just as fire-prone.

On a subsequent point:

I'd be 100% happy with the ring circuit idea if it included that / similar system and changeda few details

1)Face up to the reality that 90% of appliences regardless of their wattage/fusing requirements are fused at 13amps. Given the fact that they're all specified for use with 16amp european outlets this is not a problem.

2)If the UK is going to remain with BS1363 in the long term it could at least introduce fused sockets (at 13amps) that allow the connection of Europlugs (the narrow type only!) as well as BS1363. This would remove the need to jam europlugs into sockets having released the shutters with a screwdriver/pencil etc which does happen quite a lot. It could be designed in such a way as to exclude the larger pinned schuko/french plugs requiring grounding and automatically is incompatable with Italian/Danish/Swiss grounded plugs due to their prodruding pins.
It would prevent any applience from being plugged directly, for any reason, into a 32amp ring. (Poorly designed unfused adaptors, unfused transformer plugs etc etc)
I know it's a comprimise sollution but it would bridge a gap between the UK and European systems much like the Schuko/French design (CEE 7/7)

These sockets could be required on all new installations .. ring or radial. Old sockets simply wouldn't be able to accept Europlugs (unless you force them open.. which already happens)

I would see no reason to change the specificiation for a normal BS1363 plug though. an extra fuse never did anyone any harm and they're a good design.

On price/practicality.. sockets are expensive once-off investments. Many of them have switches etc in the uk so adding a fuse isn't a huge deal. I've seen flush fitted dimmer light switches in Ireland which have BS 1363 fuses slotted neatly into a fuse carrier the bottom for example. I'm sure a neat sollution for sockets could be developed.. (perhaps a plug in fuse like a car fuse?)

Such a socket would be very useful to the hotel industry for example.

3) For items that require specifically low fusing.. shavers and perhaps some lamps (with old style cords) or anything that needs to be fused at lower ratings: produce moulded on or rewirable plugs (for older fittings) that only accept the correct fuse type.
E.g. a 3amp plug should only accept a 3amp fuse! I'm sure this could be easily achieved.
Most people just jam a 13amp fuse in when a 3amp one blows not realising why its there in the first place. This is the very reason that systems like Diazed/Neozed are designed to make it impossible to overfuse a circuit.

Perhaps non-overfusable version of BS1363 could be developed? BS1363/B ?

As for other safety requirements: read my post in: https://www.electrical-contractor.net/ubb/Forum9/HTML/000303.html (Re offically proposed RCD requirements in Ireland)
Specifically:
From an ETCI (Electrotechnical Council of Ireland) proposal:
Recommend (to TC2) that all 230/400V electrical circuits be protected by independent RCDs, i.e. sockets protected by one RCD, lights by another
and fixed installations by one or more other RCDs. Smoke detectors and associated emergency lighting should make this proposal easier.
Sound reasonable?

[This message has been edited by djk (edited 05-14-2003).]

Steve, James,
Welcome to ECN!

I'm come across a ring where each end terminates on a separate fuse as well. It just goes to show how inventive the DIY bodger can be at coming up with ways to get it wrong!

The scope for bad connections causing an overload is one of my concerns over the system. Sure, a bad connection can cause problems anywhere, but too often I've found a ring with broken continuity on one line. The householder doesn't notice, of course, because every outlet still has power. Maybe the chances are that his use of the circuit won't ever cause appreciable overloading of the single cables now feeding the outlets. but it's really an accident waiting to happen.

Are there any statistics on how often a broken and overloaded ring has started a fire? I very much doubt it. I think the investigators just chalk up any wiring-related fire to "electrical fault" and leave it at that.

The continuity-checking ring-circuit breaker sounds an interesting idea, but just imagine how much the things would cost when they first appeared. I suspect that by the time they were being made in sufficient quantities to make them reasonably priced that the IEE and other UK institutions would have finally capitulated and abandoned the ring circuit.

pauluk

What do you think should be done about this obvious danger? Do you think radials should be used or some other method?

once heard of a tree like system with a main line ( trunk ) 4mm2 and branch like legs jointed off in 2.5mm2.

NIGHTMARE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Ring continuity checker.

Maybe have two seperate terminals on the load side of the breaker, one for each end of the ring. If the demand difference exceeds a certain amount - or if any one side exceeds 20A (for 2.5sq.mm twin+E) then trip. Sorts out broken rings and inbalanced loads.

Interesting idea Hutch, but it would need to be a double pole device with similar tests on the neutral to be fully effective.

Our newest members might like to look back at these threads where we have discussed rings in the past: www.electrical-contractor.net/ubb/Forum9/HTML/000004.html www.electrical-contractor.net/ubb/Forum9/HTML/000031.html

The "trunked" system mentioned in an earlier post was sometimes used in old buildings here. It's a similar idea, in some ways, to a ring main. Long gone though.

Consumer Unit (small number of high rated diazed fuses) feeding:

Very heavy radial cables that fed zones (similar diameter to cooker circuits.. 40-50amps)

Each room in a zone had a little fuse box (consumer unit) at ceiling level (usually consealed very neatly) with a small number of diazed fuses on a board inside serving lights, sockets (usually schuko or sometimes BS546) and occasionally individual fuses for fixed appliences like heaters.. It avoided having to run endless cables back to the consumer unit and I guess it was useful when wiring big old georgian and victorian houses that never had electricity and would have used gas lighting until the 1920s and 30s and even later in some cases!

It's actually quite a neat system, often metal ducting for cables followed the same routes as the gas pipes they replaced. This old pipework consisted of larger trunks tapped off to lights and heaters with small feeder pipes.. (a bit like spurs)

(Gas lights were still in fairly common use as late as the 1950s!)

I presume this system was used elsewhere?

[This message has been edited by djk (edited 05-18-2003).]

I've seen the sub-panel system like this on several rambling old Victorian houses in this area.

The layout wouldn't have been designed that way from the outset. It's just that the places have had wiring extended over the years and with the solid brick wall construction a single big sub-feeder to a particular area was probably the easiest way to do it.

One house I worked on a couple of years back in Cromer had an assortment of "fuse boxes" all over the house. It was a huge Victorian house that had been used as a guest-house in more recent times. I kept finding small panels tucked away all over the place, some fairly new, others dating back to the 1930s.

You can do quite a bit of detective work in these places and trace what must have been done. In a cupboard under the stairs was a small 4-way fuse panel below which I found the chopped off remains of what had obviously been the original service to the house. The "new" service entered in an extension which had been built at the rear, and this old 4-way panel had then just had a sub-feed run in from the new position.

At that "new" service entrance, extra circuits had clearly been added piecemeal over the years. There were no less than four separate 4-way panels there, and they were all daisychained! When somebody needed extra circuits, they had obviously just fitted another 4-way panel and then used an existing branch fuse as the sub-feed for it. Move the original circuit from that fuse onto the new panel, and "Voila!" Three extra spare fuse positions!

There were 13A sockets and even a whole panel, if I recall correctly, run on 5A fuses! Some outlets must have run through about 6 or 8 daisychained panels!

The distribution was an absolute mess. In the end I got it down to a main panel at the service entrance, a sub-panel under the stairs for the downstaits and another sub-panel for the upstairs section.


[This message has been edited by pauluk (edited 05-20-2003).]

The ones I've seen were generally quite ok. Highly structured and all installed to a high standard.

The fuse boxes were always Diazed never re-wirable. Nice little panels that fitted neatly into the plasterwork with a door on the front. These were the "posher" houses occupied by the snootier members of society so they had to look the part.

The fittings were usually nice brass tumbler switches mounted on carved teak plinths and the sucho sockets were recessed into similar plinths.

Usually 5/10 amp.. 16 amp was relatively rare other than for specific items like kettles, washing machines etc.