A Question for Real Electricians ?

[Andrew Mawson]

Horrid fatigue / work hardening issues with aluminium - lots of expertise in the US as loads of aluminium wire used during the Rhodesian coppper crissis.

AWEM

[The Natural Philosopher]

strictly use ally crimps. Anything else creates a nasty corrosion potential.

[Alex]

In article , Bill writes

In a previous factory job I worked with a wide range of crimps.

The training literature I saw said that crimps should not be used on solid core wires, unless designed to do so. I do not know if the insulated crimps in the article are suitable for this.

I see the tool featured in the article is the same as the one I own, and having used the proper tool at work I think it is quite frankly crap. The crimping teeth don't line up with the crimp properly. The teeth for the insulation part are exactly the same as for the copper part, and are not adjustable for different thickness insulation. The jaws do not close in a parallel fashion, making it difficult to produce a crimp that's not twisted (more relevant for spade/ring crimps).

I have used this tool, but only after cutting apart a spare crimp to work out how to line up the crimp in the tool.

Bad crimping can most definitely crush the wire, even through the insulation on that part of the crimp.

To the original poster, I'd say use the choccy blocks. Fuck what the regs say, it's simple, accessible, replaceable and safe. If you mess up a crimp, you'll have to cut it off and try again with an even shorter wire.

[Dave Plowman (News)]

Given 1, 1.5 and 2.5mm TW&E are solid core and these pre-insulated crimps are designed for precisely this job I'd think they are suitable.

There are literally thousands of different crimp tools for various applications. So unless the 'one you had at work' was specifically for these red blue and yellow pre-insulated types it's unlikely to work properly.

Eh? You use the shoulder in the insulation as the guide to where the crimp goes.

The insulation of the cable should butt up to the actual crimp so the laws are the same for both.

The amount of 'twist' over the actual crimping distance is tiny. Certainly not enough to notice with some practice.

You use the ratchet action to only just grip the crimp then push it through so the shoulder stops on the jaw edge.

Then you're either not using the correct crimp or correct tool.

The regs allow either where the joint is accessible - and inside the backing box is accessible. If plastered into a wall the usual method is crimping - choc blocks are *not* acceptable

[The Real Doctor]

Hmm. It generally means that one wire is badly gripped on both sides - because the chances of the screw nipping both equally are rather low. Which means there is a good chance that the same wire is badly gripped on both sides, which is not necessarily a Good Thing.

Ian

[Frank Erskine]

Can you please explain that further?

[John Rumm]

The crimps shown in the picture are designed for solid core applications. Some versions have internal serrations to aid gripping solid wires.

Not sure I follow that. The tool pictured does not have teeth as such - just recesses into which you place the body of the crimp.

Most solid wire crimps have a slight widening of the insulation by the end of the metal part of the crimp, so you can position it correctly in the jaws by closing them to grip the crimp lightly, and then sliding it along until the widening bit hits the jaws. As shown in:

?title=Image:CrimpingTheWire.jpg> The teeth for the insulation part are exactly the same as for the copper

You are not supposed to crimp the insulation part at all with these.

Given you are only moving them through a mm or so, any rotation is going to be negligible.

Could you not just look into the end of a new crimp before you use it to work out where the metal ends?

It can, but in practice it is hard to go wrong with T&E cable and the crimps pictured.

As has been mentioned, the regs *allow* the use of choccy blocks for the OPs application anyway. The only time you can't use them is when the joint will no longer be accessible later (say when buried in plaster).

IME, I have seen joints fail at screwed connections far more frequently than at crimped ones[1]. The two most common failures being a connection under tightened or working loose due to thermal cycling or solder creep on tinned ends (which should be cut off), or wire fatigue due to over tightening - typically on earth wires. Screw connections on the accessories themselves are usually worse than those in choccy blocks though since it is harder to do up a choccy block as tightly.

[1] which will be partly due to seeing far more screwed connections in the first place, and never having seen a failed crimp connection.

[Dave Plowman (News)]

It's not just the screw that 'does the work' but the contact between the conductor and the connector body. Which is why crimps are generally better

- a larger contact area which if properly made is less likely to corrode, etc.

An ideal connection has the maximum contact area. This can be conductor to conductor or conductor to connector.

FWIW all the higher current connectors you'll find at home use two screws in exactly the same way - have a look inside your CU.

[TheOldFellow]

joke begins: Strange that no-one mentioned annealing the wire with a blowtorch before repair to rectify any work-hardening. :joke ends.

R. IANAEE

[Huge]

The recently installed overhead supply to my house is Aluminium.

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Frank Erskine saying something like:

I doubt it, because it sounds like bollocks.