ECN Forum Forums General Topics of the Trade Non-US Electrical Systems & Trades Twist conductors?

Single stranded wires were indeed a bad idea. No doubt they will be phased out eventually.

I have done current load testing on electrical accessories like switches and sockets where I ( electrician ) twisted the wires and my colleagues ( graduate engineers ) simply stripped the wire and shoved it in the terminal and tightened the screw until their screwdriver snapped. The temperature rise on the terminals with my twisted wires was always lower.

As for the mechanical strength of the twisted wires, if you don't nick or mash the copper with your pliers its all good.

I don't think it makes any difference with wire nuts because the wire nut twists the conductors as you tighten it.

Oh yeah PaulUK and Gloria, if you have seen a Conductor do the Watusi then he would certainly be twisted.

I always twist stranded wire as long as I don't use ferrules. Never twist solid wire though, just makes it harder to get it into the terminal. Our choc blocks are usually that tight you won't even get the wires in if you twisted them before.

If I insert one single wire into a big terminal tunnel I do bend it back, otherwise I don't. Again, using ferrules you can't do that anyway, and in theory you're required to use them. For that reason i think it's much quicker to work with solid wires inside walls.

kiwi,
That's the big thing about wire preparation, there have been arguments here, over in the US Area about stripping wires and nicking the copper strands.
It seems to get worse with flexible cords too, with more strands that can be damaged at once.
However, if you are careful and keep you eyes on what you are doing, it's a cinch to strip wires properly.

Spare a thought for the poor guy investigating a fault on a circuit with twisted conductors! Perhaps stranded should be fitted with ferrules and solid just bent back on itself.

I solder 'em, after twisting. Electrical, not tinman's, solder, cored resin, as taught as an apprentice- strip (proper tool), twist, tin/load a clean iron, apply heat, remove iron as soon as solder flows, wait for it to cool. No problem getting wire in the hole, ALL the strands conduct, a good contact with the screw, no punctured fingers, if I need to do a modification it's easy, and no aggro, (except the burns!) I think it sometimes saves time, especially working in tight spaces. Do you think that soldering is generally uneconomic for trade work?
Alan

For devices [where you have more than one wire under a terminal] I like the uninsulated ferrules. I even use them in plugs.

I agree with you re: the person testing for faults.

Alan, I was taught by one of the electricians when I was a trainee to ALWAYS tin flexible stranded wires, but then I found loose connections due to 'cold flowing' of the solder under the pressure of the terminal.

I do think it depends on the type of terminal to a great degree, the tunnel type terminals with the screw bearing directly on the wire don't seem to do well with solder, but the flat gripping ones do.

As to economics, sadly I think that the climate today in general prohibits soldering in the field due to the time and skills required.

As Paul can no doubt attest, in years gone by, all telephone connections at the exchange were hand soldered, individually. Old Post Office handbooks for linemen even give temperature levels and heating instructions for different types of iron, what fluxes to use, etc. Now it's all punch down IDC connections that are considered bad if they take more than 1.5 seconds/wire.

[edited to correct verbosity, then more verbosity added to answer Alan]

[This message has been edited by chipmunk (edited 05-12-2005).]

For sure. You could see a main or intermediate distribution frame with literally thousands of soldered terminals, both for the fixed lines and for the jumpers.

One of the tasks set for early-stage apprentices was to wire up a large multi-pair cable on to a terminal block on a dummy board, correctly identifying the pairs by color code and putting them on the block in the correct sequence, soldering all connections properly, and then neatly lacing the wiring.

The other problem with soldering them is that solder has a higher resistance than copper and melts with high currents.

On a properly tinned wire end, the solder thickness is minimal, which is why you tin the IRON to contain just the right amount, and not blob a 'larrup' of solder on after the melt. Then, conduction is through little more than a tinned surface, and loosening by plastic flow of solder is not a problem. I believe that 60 years ago they soldered the Mains Cables under the roads- I have a memory of Electricity Board linesmen down a hole, with an iron-pot of solder on a coke brazier,- all the rainbow colours on the surface of the metal fascinated me. Paul's post about the soldered tag joints bought the memories back-
Jim Plaster hovering overhead- "You only need to tin the end, boy, you're not butterin' toast! Put it square to the tag, No SQUARER! Iron ON! Iron OFF! - Hold that bleedin' wire still, boy! Ah!- nearly perfect, another 25 years an' you'll be as good as me!" Then, picking off every last molecule of resin with a spike and lacing it all up like a Sunday-Roast, with that wierd stretchy Hellerman black lacing. The burns were the worst thing- you got inumerable tiny splashes of solder or resin on your hands, and these seemed to increase as the square of how many you already had! Ferrules are something I've never used- but this sounds a better way to get a good joint. I've got a big wiring job coming up- renovating the 'old' end of the house with underfloor heating, both floors, 3 zones, all with programmers, thermostats, pumps and solenoid valves. I assume the ferrules match the wires gauges? Are these available in the UK, and are any special tools needed?
Alan

That's a yes, yes, and a yes.

The tooling, especially the good (=expensive) ones, are the biggest put-off from useing ferrules. I think it's fundamentally better than soldering as when done correctly (=crimped once!) it produces a cold weld joint. The downside is that the ferrule is bigger than the bare wire.

There many places where solder causes problems. Radio amateurs will be aware of the loop aerial made from copper ef or sr plumbing fittings; they melt with high transmit power. Melting and electron migration effects in solder are also likely if used with contactors or circuit breakers that get fairly hot in normal use.