ECN Forum Forums General Topics of the Trade Non-US Electrical Systems & Trades Ring circuits again!

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).