Ring Mains; ends to different breakers?

[m__murray]

Morning all,

I've just moved into a new (to me) 1950's ish house, and as part of my moving in, decided to identify which circuits are which breakers are at the CU.

I have two mains rings (upper and lower floors) that have the ends connected to two breakers.

I have found one uk.d-i-y thread dating from 1999 suggesting this as appropriate when connecting more than 10 computers on a single ring, but have not come seen this in anywhere I've lived before. However, this is also the biggest place I've lived, so maybe that's it.

So...

1) Is / was this normal practice at any time? 2) What's the likely impact ? (breakers not tripping in the event of a fault?) 3) How urgently (if at all) should I look to change it?

thanks in advance, Michael.

[Christian McArdle]

Please explain less ambiguously.

Do the ends of each ring go to the same breaker, or one end to one breaker and one end to the other?

You are probably getting confused. There is a type of earthing called "high integrity" that should be used on computer rings. This involves using different terminals for the earth conductor at both the consumer unit and at socket outlets. This means that if one terminal becomes undone, it doesn't totally disconnect the earth. It is advisible for all ring circuits, if the socket outlets have 2 earth terminals.

Well, if the ends of a circuit have ended up in 2 different breakers, then it is a dangerous fault. It has never been allowed and should be fixed rapidly.

Quite possibly. It might be possible to seriously overload the ring under some circumstances. If the current balance is even on both legs and the other ring is unloaded, you might be able to draw 64A through a single ring circuit.

Pretty rapidly. It is a simple fix.

Christian.

[m__murray]

apologies for the ambiguity... There are 2 rings in question, with each terminating (independantly) at

2 breakers; making four breakers used.

Ring A (downstairs); 'starts' in breaker 1, 'ends' at breaker 2. Ring B (upstairs); starts in 3, ends in 4.

re: overload; That's what I thought....

M.

[Christian McArdle]

What sizes are the breakers? Why do you think that they are continuous rings and there isn't just 2 radial circuits on each floor? (Did you continuity test, or trip breakers to check behaviour?)

Christian.

[m__murray]

Christian,

I tripped the breakers to test. All downstairs sockets remained live with either breaker 1 or 2 off, but dead when both 1 and 2 off. Likewise upstairs.

I'm afraid I don't have the sizes to hand. I found this out about 2 weeks ago, and it just occured to me to raise the query in a quiet moment at work today.

thanks for the quick responses... M.

[Christian McArdle]

Given that you have discovered such a major schoolboy error with your installation, I'd advise you to get an electrician in to do a full periodic survey. You don't know what other little nuggets the muppet installer has left for you.

Christian.

[m__murray]

(quick phone call later; they're all 32A)

M.

[Frank Erskine]

On 17 May 2006 03:33:26 -0700, m_ [e-mail] had this to say:

This was common practice at one time (in the early days of ring mains), according to a retired leccy friend of mine; however this would have been long before breakers were common rather than fuses.

It should be a straightforward job to correct it.

[David Hansen]

On 17 May 2006 04:03:58 -0700 someone who may be m_ [e-mail] wrote this:-

Then you need to sort it out urgently.

It is only on industrial scale electrical systems that two protective devices may be needed to feed a circuit. These will be arranged so that if one trips then so does the other.

[m__murray]

That's pretty much what I expected to hear.

thanks for the help, M.

[m__murray]

Thanks David, I didn't think it was standard.

I'll get someone in to sort it out. (Any recommendations? - I'm in Edinb too?)

M.

[Roger]

The message from "Christian McArdle" contains these words:

I have discovered several nasties here over the years. By far the worst was the sockets for the kitchen all wired as a single radial connected to the only ring main that the house then had by the simple expedient of baring the conductors, twisting the ends from the radial round the main conductors, wrapping with insulation tape and then burying deep in an upstairs concrete threshold.

Wires are buried in the plaster (without conduit of any kind) and at all sort of odd angles. Wires running vertically or horizontally from visible fittings were a minority.

Then there was the earth from the consumer unit terminating at a rusty nail pushed loosely into the stonework. It now goes to an earth spike but I remain unsure whether it is necessary or even desirable given that the earth is also connected at the company fuse housing.

The latest discovery followed my 2004 switch to a split consumer unit. Subsequently turning on the outside light fired the RCD. It turned out that the neutral and earth for the ring main had been cut and choc blocked to give a return path for the light (the live for the lights is looped via the light switches) despite the single wire neutral for the lights being closer. I haven't as yet discounted the notion that it was done that way to provide continuity for the earth but given the other bodges casual carelessness is more likely.

[Christian McArdle]

Especially as it would have been two 15A fuse wires, rather than 2 32A breakers. At least it would have provided overcurrent protection, although it would not have been ideal.

Christian.

[David Hansen]

On Wed, 17 May 2006 14:20:41 +0100 someone who may be Roger wrote this:-

Unlikely to be a good long-term joint, due to the action of the concrete on the copper. On the other hand concrete will suppress any tendency to burst into flames:-)

How many sockets were on this spur?

When did the requirement come in? IIRC it only came in with the current edition, previous versions being silent on the issue.

[Roger]

The message from David Hansen contains these words:

It was well wrapped with insulation tape but the twists round the ring main conductors were slack.

I can't now remember. Probably only a couple. The whole house was rather short of sockets. There was another socket on the cooker outlet which occupied the 3rd way of the 3 way fusebox.

No idea. The wiring I am referring to is not recent. It was done some time prior to 1978. Some of it possible well before.

[Andy Wade]

12th June 1987, by dint of an amendment to the 15th Edition.

[Andrew Gabriel]

This was allowed (and even suggested) when converting 15A round pin radial circuits into a 30A ring circuit, in the early days. In practice, I don't think many such conversions were done, although the 30A ring circuit was designed with such conversions in mind.

[usenet]

It was certainly how our approx 1949/1950 ring main was wired, there were two 15 amp fuses in huge porcelain carriers one at each end of the ring.

[David Hansen]

On Wed, 17 May 2006 17:38:49 +0100 someone who may be Roger wrote this:-

In Ye Olden Days, unfused spurs with two single sockets was a standard arrangement (ie it complied with the regulations).

[David Hansen]

On 17 May 2006 05:53:44 -0700 someone who may be m_ [e-mail] wrote this:-

I would do it myself, so cannot recommend anyone.