I've answered a query about the old British voltage-operated ELCB recently, and thought it a good opportunity to dig one out of my junk box and post some pictures.

This is the Crabtree E60 type, which was quite common in rural residential use in the 1960s and early 1970s. These old units were quite substantially built compared to their modern RCD counterparts, and this one is about 7 x 2 inches overall:





The supply enters via the top terminals, while the lower section contains the load terminals and the connections for the operating solenoid:



The lower cover displays a test instruction for the customer:


Along with some specifications inside:


On the rear is a small removable paxolin panel which gives access to the test button contacts and associated wiring:





{Continued next message...}

[This message has been edited by pauluk (edited 01-09-2004).]

And finally, the main mechanism and switch contacts. The solenoid coil is just above and to the left of the yellow test button:



Another view, clearly showing that the main contacts are open:


Note that the operating toggle is the "free trip" type, so the breaker cannot be held closed against a fault.



[This message has been edited by pauluk (edited 01-09-2004).]

Hey great pictures Paul!,
As I am sure, we are all aware that these are not old RCD's, these are Voltage-operated, not Current operated devices, that we are all used to.
Actually Honeywell used to make all of the gear we used here, them and GeneralElectric.
This sort of gear is pretty rare here now, it was really only installed where the basics of the MEN Earthing system, couldn't be provided.(0.2 ohms between the earth stake at the transformer pole and the Installation earth)

Over here, PME (MEN or TN-C-S) in the past was confined to those rural areas where it was difficult to obtain a satisfactorily low reistance value with a ground rod. Each PME distribution system required consent from the Secretary of State for Energy. Thus the majority of rural areas with overhead distribution had homes where the ground rod was the sole method of earthing (TT system), and the ELCB was therefore very common.

PME has only really come into much more widespread use over the last 20 years or so.

Urban areas always had TN-S systems with the cable armor acting as a separate fault path right back to the transformer, so the ELCB was pretty much a rural device.

Paul,
We use the TN-C-S if my interpretation of the term is right.
TN-C-S systems where the neutral and protective functions are combined in a single conductor but only in a part of a system.
Is this the correct interpretation of TN-C-S?

If so thats the system we use in Australia.
We use a MEN system where the neutral is bonded to earth at Transformers, every few poles and at the earth stake at the consumers residence.

Am I right to understand if that system is used in the UK, you must have a voltage operated ELCB protection on the Main switch in case you get an open circuit main neutral?

If so we are not that fortunate here as a broken service neutral can result in a raised potential of any earthed metal part and there is no protection to stop this happening.

Gidday there Dapo!.
Just a small question,
With respect to Neutral and Earth Busbars in switch-boards, when our Regs changed here in 1992, we were told that you were no longer allowed to connect the Main Earthing Lead to the Neutral B/bar, which was where it had been connected to in all the houses wired previous to this change.
The Main Earth lug, was usually placed on the same stud as the Main Neutral and the Neutrals of the Range and the Hot-Water Cylinder, was this ever the case in Australia at any time?.
Nowadays, the Main Earth is required to be connected to the Earth B/bar and it is actually illegal to fit it to the Neutral bar, there must be a link that can be readily removed for testing purposes.
Just wondering.
Oh, sorry Graham, what I forgot to mention was the fact a lot of houses here, never even had an Earth Busbar, but just had a Line Tap in the back of the switch-board that was joint to a thick wire, (normally 7/.036") and that connected to the Neutral bar.
And to a certain extent, quite a few houses here didn't even have 3 core wire or a suitable Earth Electrode!.

[This message has been edited by Trumpy (edited 01-12-2004).]

Dapo,

yes, that's the system and no, the voltage operated ELCB was for use on TT systems where the neutral was not bonded to the earth. An earth fault caused a raised voltage on the earth rod which then tripped the ELCB. Today an RCD would serve the same purpose. But your idea is interesting! It would provide a means of eliminating the dangers associated with loss of neutral.

Paul,

They were used in exactly the same way on TT supplies in Ireland although the ESB would have determined when they were necessary and installed them after the meter as part of the service. The contractor just installed the fuse board and internal cabling.

TT supplies here are, however relatively rare. The ESB has full authority to choose the most appropriate earthing system for a particular supply / group of supplies. They never needed to consult any political / state athority to do their job and seem to have always favoured avoiding TT where at all possible.

ELCBs were also regularly installed on normal supplies too though as an optional extra safety device before mandatory RCDs arrived in 1980. Plenty of urban houses would have had them along side a big panel of diazed fuses.

Most rural supplies here are hooked up as individual taps into the 10/20kV 3-phase distribution system using pole mounted can-type transformers feeding a 220V supply into the house via a short cable drop (usually a twisted pair) / underground cable. I am not 100% sure what the general earthing / neutralising arrangements are with those supplies.

Any ideas?

I know very little about rural supplies in general other than what I've read / observed.

excellent pix Paul


i can't help but wonder when CMP-2 here will smarten up and realize the 02' nec states 'international' on the cover

btw~ nec digest held a neat little article on CMP-2 dealings, quite a lengthly backpedalling for that rag

for those of you whom this is unclear to, imagine installing 40 of these little jems in a panel instead of one...

~S~

The voltage-operated elcb system is now obsolete, their use has been prohibited under IEE regs since the mid-1980s.
They were never that popular in this part of the UK, probably due to local soil conditions. I've seen very few of these devices in service, by far the most common method of earthing I find in older rural installations is PME (TNC-S) where the main earth is terminated in the supply company's neutral block.
A large proportion of older installations are only earthed via the water pipe, which can provide surprisingly good (low) earth loop impedance values, providing all the supply pipes are still metallic. This method of earthing is also now (since 1966) prohibited, although equpotential bonding of metallic service pipes is mandatory.
Where I find old installations without suitable TN-S or TNC-S earthing facilities, the local PoCo will provide an earth terminal, usually free of charge.

Here in vienna TT was very common untl very recently. Only with the 1998 ETV changes TN-C-S was introduced as a mandatory grounding system. Where older houses were upgraded grounding was usually done via water pipe until 01/01/01 (great date, isn't it?), especially if only single apartments were upgraded without changing the main service. I've seen (and installed) systems with individual ground wires from the water pipe to single outlets. Eg. a standard kitchen (bit shoddy wiring): ungrounded outlet next to the door. Ground wires from water pipe to two receptacles, feeding 2 more. That was all. No RCD, no ELCB, nothing. 10A Edison base breakers, two of which never tripped, maybe due to previous shorts that had damaged them (some sparkies had a method of hitting those breakers with a hammer in order to reset them, the next short/overload was usually terminal). Usually kitchen sockets were (and often still are, old wiring isn't upgraded too often) the only grounded sockets around. When I renovated said kitchen i took the ground wire to a junction box and weired everything else. When I rewired the whole run all the way from the fuse box a few years later that setup had to go. Now the water mains is plastic anyway. Still I suppose at least one apartment has some sockets grounded to the useless water pipe. Removed 2 of these myself, but I guess the ground connections wouldn't have helped much anyway (the entire copper pipe was totally corroded). One was disconnected at all when the plumber installed the "new" gas water heater some 20 years ago. Just cut the wire and left it hanging in mid-air.
ELCBs were sometimes used but pretty rare. The few I've seen were absolutely huge beasts, usually mounted on the wall besides the panel, or inside a panel like the one shown in the Diazed panel thread.

Sparky,

NFPA on the topic of using the NEC internationally:

With its comprehensive requirements, NEC would be a more appropriate base document for the development of national wiring rules in terms of uniform application and enforcement. Few changes would be necessary to adopt the NEC because it is a model code.

The term "ELCB" was also applied to many current operated devices (RCDs). I've even seen modern Hager RCDs with marked as ELCB on the distribution panel


Some of these terms just stick!

For those new to the forum, we have diagrams of the different systems used in the U.K. in the technical reference area here.

In the modern nomenclature, the systems are designated as follows:

#1: TN-S. Seperate earth path right back to the transformer, usually via the armor of the underground cable.

#2: TN-C-S. Also known as PME (Protective Multiple Earthing), the same as the MEN system down-under, with a neutral-ground bond at the service entrance and multiple grounds on the neutral along the distribution route.

#3: TT. Local earth only, with an RCD (*).

#4: TT. Local earth with a voltage-operated ELCB.

As David pointed out, the latter system is obsolete and was removed from the IEE Regs. as a permissible arrangement in the 1980s.

Certainly in this area of Britain though, the soil conditions enable quite acceptable earth resistance values to be obtained, and there are still many rural houses with one of these devices in use.

(*) As pointed out, the term ELCB was also used to refer to the forerunner of the modern RCD, qualified as a current-operated or current-balance ELCB where distinction between it and the voltage-operated ELCB was necessary.

In later years the current-operated ELCB was renamed RCCB (Residual Current Circuit Breaker) before finally changing to RCD (Residual Current Device).

I've never liked the term RCD, as I feel it to be far less descriptive than the earlier terminology.

Trumpy,
We can still have the main earth conductor going to the neutral link here. Although it still as you said needs to be able to be removed for testing purposes.

Some electricians solder all circuit earths to the main earth and leave a long enough tail on the main earthing conductor.

Others use an earth bar for the earthing connections and run a link from there to the neutral link.

Some run the main earth conductor through the earth link and carry it on to the neutral link, so that they haven't broken the earth conductor.

The greatest problem occurs when they remove the link to test the electrical installation and forget to replace it after.

Unfortunately most times it won't be found until some time later, usually after an appliance has become faulty and someone has received a shock.

My personal reminder is to record a message in the voice recorder I carry. Just after I replace the MEN link I record this. That way when I listen to the work I have done for the day and hear myself say replaced MEN link at ## Street. I have no lingering doubt that I may have been distracted while testing and forgot to replace the link.

This may seem a little over the top, perhaps age and learning from others experiences is making me a bit trepidatous.

Sorry rambling on and a little off topic.

C-H,

It would be nice if there was protection against the loss of a main neutral conductor.

I though if the was a device that incorporated a comparator circuit.
We could have it measure the main neutral current and compare that to the current through the MEN link.
If the current in the MEN came within 10 or 20% of the main neutral current. We would know that we may have a high resistance neutral. This could then trip the protection device.

The only time it would trip when it shouldn't is when, a active to earth fault occurs on an appliance.
This would give a high level of current on the MEN link until the circuit protective device operates.

A time delay incorporated into the device would stop this type of tripping.

There may be something on the market that does this already?

There may also be great holes in my theory, let me know if there is?

Remember I am talking about a system like this where the TN-C-S earthing is used.

Again the number of times that the supply neutral fails may not warrant this type of protection.

Does anyone know if there has every been a fatal electric shock from the rise in earth potential caused by the failure of a supply neutral?

In the British PME/MEN/TN-C-S arrangement we still keep the neutral and earth busbars in the main distribution panel completely separate. The bonding is then accomplished with a cable run from the earth busbar back to the service neutral block ahead of the meter.

Here's a pic to demonstrate the point at which the PME bond is made -- Notice the earth cable running into the neutral block, just to the right of the main fuses:



This is a 3-phase service, but single-phase is similar.

Dapo,
(or maybe Norwester could answer this?).
A whole street of houses use the Overhead reticulation method, where the Neutral of the Service Main is subject to wind conditions, as is the phase conductor.
How will a loss of link between the Neutral and Earth, be dangerous, where there is a passing Earth-Potential Neutral, which the house above, is supplied from, in an MEN supply system?

As I see it, with the bond in the panel missing, the only earth-fault path would be via pipework and/or a ground rod, if fitted. You would have effectively changed to a TT arrangement, and if there is no RCD fitted, a fault would probably not result in enough current to trip an MCB or blow a fuse.

If all the water supplies feeding the group of houses have metallic paths throughout, then you would still have a fault path via the pipework and the neutral of another house.

This is one thing that really gets me going,
we opened the N-E links on a whole street fed with 230/400V MEN and got a Fault Current of 23,000A, tested at the "Consumers Terminals" (The Line-side of the Main Switch).
With the links closed, we had a Fault Current of 36,000A, at the same point.
This was undertaken during an Undergrounding Operation,that I was involved with, a new 11kV transformer being installed mid-street.

Hiya Guys,

Nothing like....MEN....urrrgggghhhh I used to hate talking about this, but I'll see how I go..........maybe another beer would be in order first...
Please also be aware that as this is only my second post here......all corrections will be appreciated.

Yes, open circuit neutrals kill plenty of people, every year all contractors in Victoria ( used to be my home state ) would get sent the *death list*.It never made pleasant reading either. Plumbers usually bore the brunt of undetected neutral faults, I think one year a landscape gardener even died whilst carrying out some unlicensed plumbing work.
Other more common problems would be house fires from earth conductor overload, more often than not it would be the house down the road rather than the house that had the O/C neutral.

The warning signs nearly always being *that* call from a customer "I'm getting shocks when I touch my taps".
As voltage rise on the earthing system is load dependant some faults would go undetected for ages. The design/nature of the MEN system also used to make it real hard to pinpoint the fault location as more often than not it would be on someone elses installation.In one case I do remember the supply authority ended up checking every house in the street...and then found the fault was at their own tranny two streets away.

As for the neutral / earth connection...well from what I can remember ( excuse the rusty brain ) the key word is *integrity*.

The disconnection of the main earth from the neutral bar or link has to be able to be carried out in a manner that does not destroy the integrity of the installations earthing system.
In an older style board ( neutral bar only ) this was pretty easy to achieve. All the circuit earths were soldered on to the main earth, the main earth could then be taken on and off the neutral bar as many times as you liked and earthing system integrity was maintained.

Things got complicated when earth bars were introduced into domestic switchboards...

Only kidding about that.....but the number of guys that used to get confused about this was pretty amazing. It never mattered which bar you went to first with the main earth as long as earthing system integrity was maintained. A lot of guys would get caught out (defected) because they would twist terminate into the neutral bar first then jump to the earth bar. The twisted up earth in the nuetral bar (unless soldered) could never be considered as having integrity once it was removed.

With regard to the "missing MEN link" what has be considered is the type of fault or overload condition.
Straight phase to neutral overload it doesn't really matter if the links there or not.
For a phase to earth fault you really have to consider the fault current path.......
Now this is were I might stuff up, ( another beer maybe.....) strictly from memory we used to be taught that under an earth fault condition approx 90 - 95 % of the fault current would use the main neutral conductor from the MSB onwards, the balance finding it's way back via the installations main earth generally through some one elses switchboard or sometimes directly to the sub or tranny depending on its proximity.
With the MEN link removed the fault current usually has no other choice than to go to ground and usually still looks for a neutral to get back on ( electricity is so lazy it never wants to work hard and always looks for the easiest path... )
What pauluk has said with with regard to lack of fault current to operate protective devices is correct in theory and can possibly happen ( particularly in areas with high ground resistance and isolated installations) but in an MEN system generally in practice fault current always seems to catch a free ride on someone elses neutral.
A single installation could have it's link out for years and even with faults nobody would be non the wiser.
No MEN link also of course means the neutral has potential for voltage rise and is floating around all over the place...which can also be interesting......

The voltage operated ELCB's used to be mandatory in rural installation areas that were suplied on the older style 11Kv SWER ( Single Wire Earth Return ) systems. Not quite sure about nowadays though.

ciao

I've noticed ESB can go to really extraordinary lengths when it comes to grounding

Is it normal run loops of grounding cable right around a building (burried in concrete) and use multiple earth electrodes?

Or is this an extreme scenario?

The possibility of neutral current returning through the grounding system is one of the reasons why British IEE Regs. specify stricter bonding requirements where PME is in use (e.g. larger bonding cables in case they end up carrying current).

Whwre PME is now being employed even in areas with good soil conductivity, there's certainly a good chance of a substantital portion of current flowing via pipework and the earth, although solid metal-to-metal connections between houses are becoming less common as metallic water services are being replaced with plastic.

By the way, in the Australian/N.Z. version of PME/MEN, do you still require a ground rod as well as the bond to the neutral?

Paul,
Yes we must still use and stake/rod at the switchboard with the men link in Australia.

If any one is interested below is a link to the MEN learning resource package used by electricians when they last renewed their licenses in Qld Australia.

The introduction has a very poignant example of the importance of the MEN system http://eso.qld.gov.au/publicat/men/index.htm

[This message has been edited by Dapo (edited 01-18-2004).]

Hey Norwester, Dapo,
Thanks for the Posts guys.
Always good to have a Down-under conversation every once in a while!.

Oh BTW Nor',
I've heard it said:
From the Chat room:
Oh, they weren't kidding!?.

[This message has been edited by Trumpy (edited 01-19-2004).]

Dapo,
Thanks for the link. That looks interesting -- I've downloaded the PDF files and will have a proper read later.

Well, I can't imagine who could have said that!

Re the Queensland paper, it makes for some interesting reading.

A few points:

• Outbuilding supplies. I see you have the option of running a separate earth conductor or of creating a new MEN bond at an outbuilding. Under the British PME arrangements, the latter isn't an option, as the bonding point just ahead of the meter is the last point at which such a connection is allowed.
• Second outbuilding with daisy-chained sub-main, pg. 46-47. Interesting that you require a soldered neutral where the sub-main neutral is looped through to a second outbuilding. I see the necessity for maintaining the neutral's integrity, of course, but I can't help wondering why soldered joints would be required at the loop-through on the first outbuilding when the diagrams appear to indicate that a normal termination at the busbar in the main panel is acceptable. If screw-terminals are deemed unsuitable for the loop through, why allow them at the point at which the sub-main neutral originates?
• Bonded service bracket, fig. 3.2, pg. 60. There are still a lot of similar service arrangements on older installations here, but generally without any such bond.
• Reporting of shocks, pg. 53-56. Am I misinterpreting something here, or as an electrician are you required to notify the power company if somebody calls yout out saying that they have been receiving shocks?

[This message has been edited by pauluk (edited 01-21-2004).]

Pauluk,

Some of those requirements may be Supply Authority ones.

I'm not sure what the UK is like, but over here we run off the SAA and local Supply Authority rules ( sometimes known as "Service and Installation" rules).

The bonding of service brackets or raisers may possibly be a requirement in Queensland, but is not required in Victoria or Western Australia to my knowledge. Unless of course double insulation cannot be maintained at the point of attachment, in which case they must be earthed. Exposed metal....earth or double insulate.

Similarly when I came over to Western Australia I noticed that over here that all metal sinks, troughs and basins must be earthed, yet in Victoria that is not considered necessary.

With regard to outbuildings, the rule of thumb is either take the earth with you or make one. I still see this botched up a lot (as little as two weeks ago......."you want me to do what with that earth".......gggggrrrrr). I'm not sure about soldering up the neutrals as I have never had to do that for the multiple type installations .....but that may be a requirement in Queensland.

The reporting of electrical shocks is mandatory in WA & Victoria and I would assume the same for other States.

In your earlier post you were talking about the size of the main earth. Our main earth size is determined by the size of the installations largest active conductor ( generally the consumer mains ). This is taken from a table directly out of our SAA Wiring Rules. ie a 16mm mains ( typically 80A service ) would require a 6mm main earth. The equipotential bond I think is still set at 4mm, regardless of the main earth size.

What I am interested in knowing is does anybody have a minimum earth stake to ground resistance that has to be met by regulation? Typically all earthing runs have to comply with meeting low resistance/impedance requirements but I have never come across a ground resistance spec other than for HV installations. I have just spent the better part of the last two years installing / upgrading our signaling system earths ( <5 ohms ) and was just wondering about this. I have been told that a typical 1200mm stake should be somewhere between 30 and 70 ohms...seems a little high to me, but I suppose that as we really rely on the supply authority earth at the nearest sub or tranny that it possibly doesn't matter???

Dapo, I downloaded that document at work yesterday...I intend to show it around a bit as we have quite a lot of very young and inexperienced sparkies here ( only because they never seem to get the exposure to the work ). Thanks for posting that, it really is quite informative. You mentioned that it was part of a licence renewal package. Do the guys in the *sunshine state* have to retest on licence renewal?

ciao

Norwester,
According to NZECP's 25 (Earthing and Equi-potential Bonding)and 35 (Power Systems Earthing), the value of Earth to Electrode resistance should be a maximum of 10 ohms.
Seems awfully low!.