Electrical question: stripping ends / crushing wires in terminals

[Neil Williams]

A basic electrical question for you all.

This hasn't been a particular issue so far, because where it did happen I played it safe and re-stripped the ends. But mainly to save effort in future (particularly where there isn't much spare left to re- strip), I'd like to be sure.

1. If, when stripping the inner insulation off twin and earth, you "nick" the core with the strippers slightly, is that likely to cause enough difference to the resistance of that core to make it unsafe?

1. Similarly, will overtightening terminals such that the wire is crushed be a problem, so long as it is not actually broken?

A test with a multimeter showed negligible/no change in resistance where I did this deliberately to a small length of test cable so I'm inclined to say "not a problem" - but am I right?

Thanks

Neil

[Martin Bonner]

The problem here is not the increase in resistance (negligible as you say), but that nick will act as a stress concentrator, meaning that the wire is much more likely to snap at that point - particularly if it is flexed at all.

I don't think that is a problem (but an expert will be along shortly to correct me). In fact, I would have thought some deformation of the wire was required, to ensure a nice gas-tight contact.

[Dave Plowman (News)]

It would depend on the size of the 'nick'. A mere scratch could be ignored

- something that reduces the diameter appreciably best not. But given there are lots of devices around for stripping cable properly, it shouldn't be a question which needs asking.

No - as the cross section remains the same.

You'd need a very specialised meter to measure this sort of very low resistance.

[jgharston]

I tend to use a small blunt kitchen knife for cable stripping, it cuts the PVC without making any impression on the copper underneath. Taught to me by my sparks instructor 20 years ago.

JGH

[ARWadsworth]

Like a pair of snips that have cut through a live cable?

[Andy Burns]

Surely you'd need to snip through 1, 1.5 and 2.5 mm^2 live cables to form the correct sized notches for everyday use?

[ARWadsworth]

I have an apprentice.........

[Andy Burns]

Lets hope he learns before he moves onto 4, 6 and 10 mm^2 cables

[ARWadsworth]

It takes too long. Any anyway, the kitchen knife is for changing plugs.

[jgharston]

The angle grinder wasn't to hand.

JGH

[Bob Eager]

Yes, I have a pair of those. Had them for 45 years...

[ARWadsworth]

Bedded in on some imperial 7/.029 T&E then:-)

[Bob Eager]

It was actually some heavy duty rubber insulated flex feeding lighting battens on a stage. I was hanging on to the (earthed) stage framework with the other hand/arm, 30 feet up, at the time.

[Dave Plowman (News)]

Ah. Forgot we had a pro here. ;-)

[Newshound]

RCDs are for wimps....

[robgraham]

Have had several pairs of those, and was oh so glad when a professional I employed at one time did the same !

Back on topic - I was always taught to nick the end of the cable and use a pair of pliers to pull out the earth line to strip the outer sheath back. And then I just pull off the required length of the inner insulation with the wire cutters.

Rob

[jgharston]

I can't quite picture what you're describing there without picturing the cable being damaged. Maybe time for a Wiki entry?

JGH

[robgraham]

OK - in words of one syllable !!

It's inadvisable to cut the outer sheath with a knife where you want it stripped back to because of the danger of nicking the inner cable insulation - agreed ?

To avoid this, extract the earth lead from the cut end of the cable by making a small nick in the face of the cut end with the wire cutters. Pull the earth wire back to the required length of exposed cable with pliers such that the earth wire cuts the outer sheath. The outer sheath can then be cut off using the wire cutters.

Judicious use of the wire cutters can then strip off the required length of the plastic insulation from the inner cables.

It's always a bit difficult to describe in words what is so easy to show as a demo, so I hope I've got the idea across.

Rob

[Andy Burns]

That bit is clear and I suspect most people use that method

I think that's the bit that JGH was worried about, using cutters rather than properly adjusted wire strippers to strip the inner insulation, you can nick the conductor unless you're careful ... but then of course, we're all careful, all the time!

[Steve Walker]

I've used that method, but I've also used another - using a Stanley knife to cut into the end, with just a slight sideways angle so that it slides smoothly down the side of the Earth core without nicking it or the insulation of the phase conductor next to it. It's much easier that way to strip right back into an accessory box.

SteveW