What's the correct way to solder twin and earth cable?

[Dave Plowman (News)]

Eh? Dead easy with ordinary combination pliers.

[meow2222]

dangerous advice. Soldering works fine, but has one weakness that catches people out: the solder is very soft and weak, and cant tolerate movement. It is therefore essential that the wires to be soldered are completely immobilised. You cant achieve that by wrapping them with fusewire, twisting is the logical thing - BUT - twist them twice as long as looks solid, else they're liable to fail.

TBH if you need instructions on soldering, dont do it. Its a fine method if done right, but its so easy to screw up and leave a dangerous joint behind. I've seen so many failures, thankfully at low powers.

NT

[Frank Erskine]

On Sun, 10 May 2009 23:10:48 +0100, "Graham." had this to say:

It's only places like Maplins that no longer sell real Pb/Sn solder. Even B&Q sell the real thing...

[Frank Erskine]

On Sun, 10 May 2009 23:30:22 +0100, "Dave Plowman (News)" had this to say:

But the OP was asking about _soldering_ :-)

[Dave Plowman (News)]

Indeed - but you need a mechanically strong joint before soldering and twisting the conductor is a good way. And is not difficult to do as you suggested.

[clangers_snout]

Actually I wasn't really asking HOW to solder, or crimp, for that matter. I'm an electronics engineer so am quite competent at both. What I wanted to know was the approved, i.e. 17th edition, method of soldering T&E. I still don't know if I got an answer to that?

[Harry Bloomfield]

I agree that solder cannot tolerate movement, which was why I suggested binding them with wire rather than twisting.

Trying to twist a single solid core would harden the copper making the joint weaker, plus produces extra stress where the joint ends - than leaving the cores straight and over binding plus soldering. There was nothing dangerous in the advice, I have done it successfully many times and it is a standard method used for many decades.

In the 1960's there was an IEE regulation taught method of solder jointing the then used 7/.029 cable. It involved binding the two ends then tinning at two points along the length of the joint, rather than tinning the entire length. It was fairly similar to a splice in a rope. The point being to provide a joint which was not only sound, but had some built in flexibility.

[Harry Bloomfield]

Either a soldered or crimped joint would satisfy that requirement :-)

[John Rumm]

The 17th edition (or any previous for that matter) does not actually specify a method by which one should solder - only that it is an acceptable way of effecting a joint.

Hence it really comes down to good practice for good solder joints that may be subject to movement (thermal expansion, vibration etc). There are general requirements for cables being adequately sheathed (i.e. individual wires and overall sheath or other protection like conduit), and the use of suitable enclosures when individual insulated wires are otherwise exposed).

[Tim S]

John Rumm coughed up some electrons that declared:

When did wirenuts go out? I found some in formaer active use the other day...

[Andrew Gabriel]

I'm not aware of any connection boxes explicitly designed for soldering. Very few electricians are competent to solder, so there would be no market for them.

17th edition doesn't tell you how to solder, crimp, or braze connections. It's covered by requirement for good workmanship.

I will however comment on the special inaccessible connection terminals which have sprung up. They seem to me to be to be completely unsuitable for the job, indeed much worse than using screw terminals. It's as though the designer didn't understand _why_ inaccessible connections are specified to be handled differently, but just designed something which doesn't use screw terminals because he knew they aren't allowed. I've only seen pictures though, not had one in my hands.

[meow2222]

I'm a bit surprised that you can isolate the solder joint from all movement and force by binding it. It would need to be 30A fusewire rather than 5A, and presumably have a fair length of binding.

NT

[Dave Plowman (News)]

Tell the GPO that - twisted connections were the norm for many a year.

[Dave Plowman (News)]

Only problems I've ever seen with screw terminals on a domestic installation is where others have done them up - or rather not. I've never had any come loose or give problems so personally would be perfectly happy having an ordinary JB in a totally inaccessible place.

[Dave Liquorice]

Can't say I've been aware of plain twisted wires. Solder tag blocks, block terminals with screws, IDC, gel filled IDC "nuts".

Wire wrapping I guess but that didn't seem to last long or become widespread, I wonder why? B-)

[Frank Erskine]

On Tue, 12 May 2009 10:10:16 +0100 (BST), "Dave Liquorice" had this to say:

Twisted joints were in use by the GPO for _many_ years in underground cables - no doubt millions of such joints are still extant. Indeed, long before that, twisted joints in various forms (Britannia and copper-sleeve) were in use for overhead open wire spans. Considerably more skill (and time) is needed to perform a twisted joint than crimps and other 'modern' types.

[Dave Plowman (News)]

Underground cable joints - twisted then paper sleeved before being sealed.