Earthing ring-main sockets

[p.scott]

Hey Folks,

I recently had to replace a ring main socket in a part of the house that was re-wired 20+ years ago by an ex-electricity board inspector. I was surprised to see that the earth connectors, instead of being wired into the socket, were twisted together along with a flying earth and connected to the earth connector in the metal box. The flying earth alone went to the socket. None of the earths were sheathed!

Previously, I would have connected all three earth wires into the socket. However, this unexpected configuration seems less likely to come adrift because the three-wire collection goes into a fixed connector and only a single wire goes to the socket. The three-wire collection only needs disturbing if re-wiring is needed, not whenever a socket is replaced.

(I recently bought a socket from Wickes; it had a square hole for the earths and I had difficulty getting three thin earths to stay in. I dislike bending the ends as they fall off if you have to straighten them out.)

Apart from the sheathing, is the unexpected configuration: legal, less safe, more safe?

TIA

Peter

[Owain]

Yes.

Not as tidy as having all the circuit wires together to the accessory, but I think can help to preserve the integrity of the earth continuity when an accessory is removed.

You could put one of the circuit earths and a link wire into the box terminal, the other end of the link wire and the other circuit earth into the socket terminal, thus having only two wires in each hole.

Lack of insulation on the earth was normal until c. 1960s.

Owain

[Frank Erskine]

That's probably why he was ex-electricity board...

[Colin Wilson]

ever wired sockets in a substation ?

AFAIK we couldn't actually book sleeving out, but the supply side isn't covered under the 16th

It would seem a little "enthusiastic" to be fair, when you consider you had live open busbars on the LV board :-}

[John Rumm]

There was a time when sheathing for the earth was not required - your installation may pre-date that.

It will have a very slight negative effect on the earth fault loop impedance - but not enough to worry about.

The main difficulty of doing it that way is often the backbox terminals doe snot have much capacity and will not as easily take as many wires.

If you get a socket with decent square terminals like the TLC ultimate one, then they are really nice to wire - plenty of terminal space and a good grip.

ok, very slightly less safe, but negligible - especially on an RCD protected circuit.

(this assumes modern 2.5mm^2 cable with 1.5mm^2 CPC. If it is older standard cable with only a 1.0mm^2 CPC then it is less desirable).

[Ian White]

Such people re-wire their own homes in one of two ways:

1. With absolute perfection that they've learned from years of experience; or
2. Cutting every corner that they've learned from years of experience.

Commiserations - I used to live in a Type 2 house too.

[David W.E. Roberts]

Some of the junction boxes in my house have a similar approach - the earth wires are all twisted together external to the junction box and unsheathed. AFAIK there was also an earth into the junction box, but there was more space and less tangle inside with only one earth instead of one from each T&E.

Now if the majority of the earth wires are external there may be no need of sheathing but I would have thought that wires internal to a box would need sheathing, because there is always a chance that one of them could come into contact with a live or neutral teminal as the socket was positioned during fitting or removal.

Still, it seems that it may have been common practice at one time.

Cheers

Dave R

P.S. which part of the country is this house in?

My house is in Berkshire and they do things differently from the way they are done in Suffolk (small things like the way pipes are fixed to walls etc.).

[<me9]

More reason to sleeve, as they could touch the bars.

[Colin Wilson]

LOL they could touch any phase or neutral more easily by going straight for the busbars - and if it's a standard 500kVA sub, many transformers are connected to the ACB via uninsulated overhead bars.

If they're already in the sub, they're at more risk from the other exposed extraneous metalwork, than by having to take a screwdriver to a socket to put themselves at risk.

That's completely ignoring the possibility of them playing with the HV side of things !

[Don]

Which means nothing! 20+ years ago people did things differently.

Why would that matter? The socket usually stays where it is.

More sensible doing it that way.

Legal with respect to which Law? People often use the word "legal" when they mean complying with an advisory regulation. This is not correct as "legal" would refer to criminal law. Sheathing doesn't matter inside the box on the back of a socket or a switch - why would it? I would connect the earth wires as you describe, but not all sockets are good quality - so if you tighten the wires the screw keeps turning.

[Dave Plowman (News)]

I'm not sure when sleeving became mandatory but it was much longer than 20 years ago. I'd say more like 40. I've seen the 7/0.29 imperial ring main cable - which 2.5mm metric replaced in about '70 - with sleeved earths.

Twisted earths - if over a long enough length - will give a perfectly satisfactory connection provided the conductors aren't strained enough to fracture. And a short tail from that to the fitting will not introduce a high enough resistance to cause a fail. But it's not modern best practice. Incidentally this was the way telephone cables were connected underground once - dunno if they still are.

[TheOldFellow]

Not quite as bad as my lighting circuit (since replaced) which had free-hanging junction boxes all over the place all wired with just the phase and neutrals in the box, and all the CPC's taken, bare, but long, under the box and just twisted together. After 30 years of people trampling about in the loft (it's a bungalow, all the wiring is in the loft), you can imagine what the impedance was.

R.

[nightjar]

I recall sheathing for earths being introduced, which would probably have been about 30 years ago. Wiring the earths to the backbox terminal used to be done to ensure that the earth circuit was less likely to be damaged when the final fit was to take place, usually in a new build, after other trades had been working in the area. Modern backboxes have fairly small capacity terminals, which would make that difficlut to do.

Colin Bignell

[mick]

That looks like a pretty well wired socket. You don't break the earth on the ring while replacing a socket and the box has to be earthed anyway if it's metal. It's actually how I was trained to wire sockets (by Norweb)

30-odd years ago. :-) The earth wires should really be sleeved though, but this was often omitted if there was no chance of them touching live or neutral connections on the back of the socket (it's mainly an identification issue). You probably found that the ring earths were wired first, at the back of the box.

[TMC]

Some 30 years ago I was taught to wire the earths to the socket (sheathed) and a single piece of insulated earth wire to the connector on the metal box. The reason given for this was that without the connection to the back box the only way the box was earthed was through the screws holding the socket and needed to be 'bonded' in case the socket was unscrewed whilst it was live. Mind you this was at the time when councils were specifying earth bonding to metal window frames.

Tony

[Owain]

I hope you're not suggesting they wired the kettle in with croc clips...

Owain

[David Hansen]

On Thu, 11 Oct 2007 09:46:58 +0100 someone who may be "TMC" wrote this:-

That is sensible.

The Wiring Regulations don't require this except, if as has already been mentioned, conduit is providing the CPC.

A better reason for doing it this way is that failure of the single conductor leaves just the back box unearthed (or to be precise subject to the vagaries of any screws).

Why councils should specify such things is beyond me. They know little about electricity and it wasn't required in the Wiring Regulations. What seemed to be common was a misreading of the wording. There were several tests about whether an item should be bonded and it was only if ALL of them were met that it should be bonded. Almost any bit of metal would meet one or two of the tests, but that didn't mean it should have been bonded.

[Colin Wilson]

No, but a 3kW cooker-element fan heater had them :-p

[Peter Scott]

Nice one! I should have said retired.

P