There's a regular debate over in the general U.S. area about whether to pre-twist conductors when using a wirenut.

So let's ask a similar question of those wiring British devices with their rather different terminal arrangements to American fittings.

When connecting multiple conductors to a switch or socket terminal, do you twist together first?

For closed types I like to get all the strands into the connector, and twisting (where possible) each wire seems a good way of doing it neatly. I'm not so keen on twisting all the wires together as that tends to shorten but fatten the length inserted.

To my mind the brass screw in threaded U style rose junction box that we have in the UK don't favour twisting; the cables compact down better without twisting allowing the grub screw to engage further.

Storm in a wirenut?

Gideon.


[This message has been edited by gideonr (edited 02-28-2005).]

Paul,
I've always twisted any wires that I've worked with.
The exception would be the larger sizes and Aluminium wires.
One aspect of Electrical work here, that annoys me, is where two wires feed a Surface-mount MCB base on a Switch-board panel and the wires aren't twisted together.
It's not the shock aspect of replacing the base live, but if the wires are carrying any sort of load, it makes for a bit of sparking.
In my opinion, pre-twisting gives you a better connection between the wires and also lessens the likelihood of cutting into the strands of the wire with a terminal that only uses a screw to hold the wire strands in the terminal body.

I never saw a conductor twist. Hmmm.

They prefer the watusi!

Good point, the terminals on most modern ceiling roses are pretty small, but then they provide enough terminal positions for one conductor per hole in most situations. You only have to double-up if you want to parallel a second light, run a second thru-feed, etc.

I think there's also quite a difference between terminal styles on other fittings which can affect this. Compare the types where the screw clamp down on a small plate versus those where the end of the screw just goes directly onto the conductors.

Well,
I'm sorry for the thread-jack here Paul, but I have a little, related question:
Where your terminal has enough space, after you have twisted the conductor, do you bend the wire back on itself, to fill the terminal tunnel?.

Not a threadjack at all -- It's a very good related question.

It depends on the terminal type and the conductors involved. On some types of socket, for example, if it's a spur or the end of a radial with just one 2.5 sq. mm conductor per terminal it can hard to clamp the wire properly without doubling it over. (Our 2.5 cable in twin-&-earth style is always a single, solid core.)

That's what I meant Paul.
It has been a convention here for years with stranded conductors that if you do have room in the tunnel to have a doubled up twist, you should do just that.
I think it comes from the strips of connectors, where there were no plates shielding the wire strands from the screw as it came down on the wire.
Driving a screw into the wire would cause it to eventually break and fail.

depends on how good the fit is i think.
I always twist my cpc's incase of terminal failing leaving them loose or out of the connection all together, by twisting them you ensure a better chance of the cpc remaining continuouse throughout the circuit,the failiure could arise at the first connection of a bank of 20 lights,
and no one would ever know the 19 other lights where not earthed (until next tested of course)where as they would soon know if there was a phase/neutral to pop out of its home!

quote
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by twisting them you ensure a better chance of the cpc remaining continuouse throughout the circuit,the failiure could arise at the first connection of a bank of 20 lights,
and no one would ever know the 19 other lights where not earthed (until next tested of course)
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Surely this is the reason why we carry out R1+R2 and measure zs to check earth loop at furthest point on the circuit. Problem with twisting you can stress the conductors specially this silly single stranded stuff, have seen more damage done by twisting and bending conductors than the terminals of the accessories do.

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.

Ahh yes,
I'm told that the solder fill method of terminating electrical lugs is still taught in Polytech's over here, which seems rather strange, because most people went out of this technique in the early 1990's, in favour of the Hex Crimp compression joint.
Even the PoCo here uses all Crimp connections.