multiple T&E cables into back box. ?

[N. Thornton]

Compare what I just wrote with America, where even the 2 screws to hold the live and neutral wires in is an optional extra.

Regards, NT

[Martin Angove]

I side with you Dave on this one. Different manufacturers have different geometries of terminals, but with socket outlets, switches and the like I have yet to see a solid wire go down the side of a screw rather than underneath it. On the occasions where the pull test has resulted in one or more wires coming loose, I have invariably been able to see either no marks at all on the wire from the screw or sometimes a small "pinch" right at the end. This is more of a problem with earth wires where the sleeving may slip slightly leading you to think that the wire is properly inserted when it isn't.

I speak as someone who regularly uses Screwfix cheapo fittings ("Select" made by Phylex I think). They aren't quite as nice to wire as some others I could mention, but they do the job reasonably well.

Come to think of it, I have seen a wire down the side of a screw. It was where someone had used 1mm2 to wire a 20A radial (don't ask). Presumably the L and N terminals are designed to take 1.5mm2 as a minimum.

Such as:

1: wires do not twist to exactly the same length. One of them isn't trapped under the screw but the pull test doesn't reveal this as the twist stops it coming out.

2: when later adding a spur you end up having to snip the twisted parts off, shortening the wires, because it is impossible either to slip a single in next to two twisted ones, or to successfully untwist a pair and re-twist with a third without seriously weakening the twisted/untwisted/twisted wires. This nearly caused me serious problems today - I was replacing a faceplate for aesthetic reasons and having to re-sleeve the earths with green/yellow instead of plain green. Because they were twisted *and* folded over I had to snip the twisted part in order to get the sleeving off. This lost about half an inch of the wire which, along with the slightly different positioning of the earth terminal in the new faceplate meant a *very* tight squeeze to get the thing back together.

At least it proved the screw was holding the wires properly :-)

Hwyl!

M.

[Rick Hughes]

Hi Dave ... this afternoon fitted a 4 gang switch and 4 x 1.0mm t&e cables ... when I put all the earths into the connection at back of a standard galv box, one of them was missed entirely by the screw ... twice, on 3rd attempt I twisted wires into 2 x 2 pairs and then no problem.

This earth connection was not a square block with a hole in it as some makes, but a u shaped galv strap pulling down on an inverted U ....... fair gaps between screw and sides of 'u'

It must depend on the make of the kit and the diameter of the conductors ...

[Martin Angove]

Point of semantics, but they are not the same thing :-)

"Optional" means "either do it or don't do it, the choice is up to you" implying complete freedom of choice.

"If neccessary" means "under certain circumstances you may be required to do this" implying that the choice is not yours at all, but rather dictated by circumstances.

Deciding when I get into my car whether to fill it up with petrol is an "if neccessary" choice.

Choosing between two petrol stations is an "optional" one.

Hwyl!

M.

[Martin Angove]

I find these terminals dreadful - and often they distort as you tighten the screw too (the boxes I have seen them on are the ones I occasionally have to get from B&Q). The others I don't like much are the ones with a loose "plate" under which you slip the earth bond but which moves about so much you can't often get the thing in correctly. These are the ones I normally get from Screwfix.

Two solutions:

1: double-up or bend over (i.e. in the latter case, bend the earth around the screw). 2: crimp a bootlace (for type 1) or fork (for type 2) or similar on to the end of the wire. This invariably does the trick. This one is useful for wires into earth bonding clamps too.

Hwyl!

M.

[Lurch]

On Tue, 1 Jun 2004 20:28:39 +0000 (UTC), "Rick Hughes" strung together this:

Hmm, the problem there is most metal boxes have wanky earth terminals. Some have good earth posts, but usually you get a cross threaded screw in a hole 5x bigger than the thread.

[Dave Plowman]

Yes, I'd certainly agree it's possible with those type of backing boxes - decent ones like MK use a proper brass terminal.;-)

I stand by my claim that it isn't possible into a socket etc if using the correct size of wire - ie the smallest allowable. If anyone thinks it is, please give the make so I can try for myself.

[T i m]

I've not fitted as many sockets as some of you guys but I have seen the 'wire go up the side of the screw thing' several times.

There seems to be 3 types of connector.

1) A tubular hole with a grub screw that come in from the side (like some faceplates). These are the ones that seem to be worst. 2) A 'saddle' that captures the wires and draws them down to a plate (like on an MCB) 3) A 'slot' cut across a threaded hole with a grubscrew (like a round junction box).

It's 1) that seem to be the worst for this and even if you bend a cable over (it's normally the earth on 2.5mm T&E as the earth is thinner but the hole isn't) either the cable or the bent bit will go up the side of the screw?

Twisting the cables together (neatly and tightly with some square nosed pliers) does solve the problem but could break the rules.

If 'an' earth wire comes loose you could loose the earth to the plate and the integrity of the earth round the ring? If all 3 fall out (ring in / out and tail to back box, still twisted together) you will just loose the earth to the socket but might still have it via the 'tail' and the screws? ;-)

All the best ..

T i m

[Dave Plowman]

You've seen all these types on sockets?

[stefek.zaba]

It's *almost* that unlikely; though the final condition is more accurately "low enough not to trip the breaker for long enough to allow the damage to be caused"; and I'm not sure why we require that the live-to-backbox short needs to be particularly low impedance.

The odds seem to be a little higher than the one-in-a-billion you suggest, as it was a fault seen in practice often enough for the IEE to remark upon it maybe 10? 15? years back, for at least one photo to appear in at least one of the classic "this is how we do wiring" books aimed mainly at The Trade (sorry, but I'm not sure which one: Stubbs, maybe?), and for the NICEIC to adopt putting in those lil' tails as Established Practice (and therefore one of the Rituals Of Trade which pickcy-NICkies love to whine on about, while letting go significantly more risky practices which aren't as simple to find... but I digress). Thus, if your wiring is going to be Inspeckchertulated, it's not really the case that

since their absense may be Frowned Upon by the Peaked Cap brigade.

Lurch's comment that the socket terminals are massively more "worthy" of receiving the benefit of the incoming earths than the backbox strikes me as right on the money, mind you: sound, tight connections of both/all three (if there's a spur going off) earth wires to the socket/other-accessory is seriously essential; tail going off to the backbox is a nice-to-have and as noted above may be needed to satisfy The Inspector. But terminating the earths on the backbox terminal and *relying* on a single strap to provide earthing on that there third pin seems like inviting risk for utterly marginal benefit - it's not as if folding the cables neatly and safely in the backbox when securing the socket in place is made seriously easier by having one or two fewer 1.0mm earth wires in sleeving to deal with, as it's the two or three lots of partly-still-sheathed 2.5mmsq L and N wires which need the bulk of the "gentle persuasion" to lie comfortably and safely in the backbox. Missing earths are an insiduous fault, as equipment will still work fine without them; and the absence of a backup path for the mains potential will only become apparent when a fault appears; so minimising the number of connections between the main earth terminal and each socket/accessories earthing point is a Good Thing.

Stefek, rambling on

[Dave Plowman]

Absolutely spot on IMHO. So probably the kiss of death.

[N. Thornton]

Well if its not low z then the socket fixing screws will do the job, even if loose. In this case the risk is no different with or without the tail. It is only when the fault z is low that the tail can make a difference to what happens.

Regards, NT