Another home wiring puzzle

[Jeff Layman]

Fortunately not mine!

A friend just told me "I have just replaced a single electric socket in our lounge with a switched double. In order to stop the supply, I had to switch off two trip switches at the same time." That didn't sound right, or safe.

DIYWiki notes: at <

:"The ring circuit cable starts at the consumer unit (fusebox]), visits each socket in turn, and then returns to the consumer unit. The 2 cable ends at the CU are connected together in all modern rings, and supplied by one fuse or MCB."

That confirms there should be one MCB, but I note the use of "...in all modern rings...". Does that mean there might have been two fuses or MCBs in early rings? I think his house was built around 1980.

[Tricky Dicky]

I rewired a house in 1983 and certainly there was no such wiring, the recommendation at the time was to to have separate ring mains and lighting circuits upstairs and down. I have seen instances where people have wired spurs off an upstairs ring into a room below which has safety implications. It can be a common mistake in houses which have solid floors downstairs as it is possible to have two ring mains running in the ceiling space one providing drop feeds to the downstairs and the other for the upstairs, maybe something like that has occurred at your friends house?

Richard

[Brian Gaff (Sofa]

It does indeed seem odd if, in effect there is now one circuit and two breakers across each other for them both. I guess isolation of the circuits and a long laborious process of checking sockets is the only way to find this, unless there is evidence of work having been done somewhere where the effect might have been caused. Mighty weird. Mine was done in 1975, and there are two circuits on both lights and sockets, plus one for a higher current feed for a cooker and a separate one for the Immersion heater on its own. I also now have a special one for Economy 7 with a higher current rating only live in the hours needed. Brian

[ARW]

There were never two MCBs .

It seems that the ring is supplied from two MCBs.

This could be like the ones I have seen where the immersion 2.5 was in the 32A sockets MCB with one leg of the ring and the other leg of the ring was in the immersion 16A MCB.

Or even worse was the two rings (up sockets and down sockets) with one leg of up sockets and one leg of the down sockets in one MCB and the other legs in another MCB.

[Chris Green]

Our house (as in the house I grew up in, back in the 1950s) had a very early ring circuit as it was built in 1949 or thereabouts. It definitely had fuses at each end of the ring. Whether that was as it should have been or just how the electrician (my father I think) thought it should be I don't know.

[ARW]

I would say that does not break any regs if the CU is labelled up correctly.

[spuorgelgoog]

When rings were first introduced, people used to make them from 2 15A radial circuits joined together.

I don't know how officially-sanctioned that was or for how long.

Owain

[Tim+]

I suspect he just means that he switched off the ring supply MCB for that area/floor and the RCD protection (which may cover all circuits) as well.

Tim

[Jack Harry Teesdale]

The same thing ocurred in a house i owned in the 1980's built about 10 yrs before.

I too found the 13A ring mains were connected to two 30A fuses in the CU.

I of course corrected it to have each ring main wired in to one 30A fuse.

On dicussing the matter with each of my adjacent neighbours, it turned out they both had the same problem!

[Roger Mills]

Sounds to me as if someone has at some time added a loop with additional socket(s) and has connected one end to one ring and the other end to another ring - thus cross-connecting the rings. Somewhat undesirable!

[Jeff Layman]

Interesting. I forgot to add that I asked my friend if he could check with other houses nearby on the estate to see if they had the same wiring as he found.

[Chris Green]

Ah, but this was a new house with new electrics, all the new fangled square pin fused plugs etc.

[John Rumm]

Not in the 80's...

There was a time when the ring circuit was first introduced in the 40's that it may have been formed from two 15A fused radials, that were joined in the middle so to speak. It was a way of creating a more versatile circuit that could be used for house heating etc, at a time (i.e. just after WWII) when materials were in short supply.

So in summary, he has some faulty wiring.

[Dave Plowman (News]

Yes- I've seen that several times, with old style fuseboxes. I suppose it's safe enough as regards circuit protection?

[Fredxx]

I can see the logic, where the two MCBs are each rated for 2.5mm cable which will allow more current be safely pulled along the ring.

I wonder if it will catch on?

Obviously you would need a common RCD.

[ARW]

Actually you do not as there will be no imbalance between live and neutral.

[Fredxx]

Any imbalance (leakage to earth) would be shared between the two RCDs, assuming they are identical. So the residual current would be close to twice the expected value before one tripped. The other would follow immediately.

[Pancho]

My house has left/right ring mains rather than up/down. Some rooms, like the hall, have both ring mains. It's often quite useful, easier to run an extension lead from rooms on the same floor than it is down the stairs.

Is this against the regs/ a mistake?

It did confuse me a couple of days ago, but more that I switched off something I didn't mean to, rather than I mistakenly left a socket live. I always physically check a socket isn't live before working on it.

[jeff Layman]

My friend just replied. He thinks that the problem must have occurred when the new CU and the new wiring in the extension were joined up to the original house wiring, 18 years ago.

Out of interest, anyone know if this was out of line with Part P then? For that matter, is it out of line with Part P now? I would have thought it was out-of-line as it represents a shock hazard - although an unusual one.

[Roger Hayter]

If either of the MCBs that feed the offending socket have more than one wire going into them then it definitely needs fixing. It may or may not be actually dangerous, but someone needs to check.