Crimps, heat shrink and phase/earth shorts - wtf?!

[Ben Blaukopf]

Just finished a day of rewiring the lights circuit in the kitchen - not finished the whole lot yet, but the main lights are done.

Test it. Short between phase and earth. Arghhh. Track it down to a section of cable with a crimp in. Hmmm. Cut out crimp, short disappears. Remove the heatshrink, inspect cable. Can't find anything wrong.

Pull through some slack, remake crimp. No short. Get the hairdryer out, and shrink the heat-shrink around the sheath. Short reappears.

It's not a dead short - it's 43ohms. I'm inclined to leave it overnight and see what I measure in the morning....

Any ideas what's going on?!

Ben

[Lurch]

On Sun, 15 Apr 2007 19:45:43 +0100, Ben Blaukopf mused:

Would this be 3 crimps on a twin and earth all encapsulated in one piece of heat shrink? If so, when you crimp the crimp there's not much left of the insulation on it as you've just flattened it. I always insulate the crimps individually before applying an overal insulation to prevent this.

[Clive Mitchell]

In message , Ben Blaukopf writes

You're definitely not heating the cable up to the point where wire melts within the jacketed area?

[Ben Blaukopf]

Nope. I completely disassembled the first one, and there was no sign of any damage whatsoever.

Ben

[Ben Blaukopf]

That's the one. I'll remake it with individual insulation. I guess heating it up is just tipping it over the edge.

Ben

[Lurch]

On Sun, 15 Apr 2007 20:15:03 +0100, Lurch mused:

Also heating it up won't help the minimal amounts of insulation left.

[dom]

Fit a heatsink and let it dissipate 1.5KW

[dom]

More seriously, maybe the real partial-short is nearby and breaking/ remaking the join just disturbed it a bit?

[Ben Blaukopf]

It's definitely the crimp - it's about 4 cable clips to anything else of note.

[Ben Blaukopf]

That's the other puzzling thing. I powered up the circuit, expecting the crimp to get very hot very quickly. It didn't.

But it is definitely the crimp that's the problem. I chopped it out without disturbing anything else - problem solved, on both sides of the break.

[tony sayer]

In article , Lurch writes

Where's part Pee come into this?...

[Lurch]

On Sun, 15 Apr 2007 21:19:37 +0100, tony sayer mused:

Dunno. Why should part p be an issue?

[tony sayer]

In article , Lurch writes

Electrix in a Kitchen?....

[Lurch]

On Sun, 15 Apr 2007 22:48:06 +0100, tony sayer mused:

Who said the crimps were in the kitchen?

[Ben Blaukopf]

Well I did say I was rewiring the kitchen lights.

Tony, I have only one thing to say. SNB.

Ben

[Lurch]

On Sun, 15 Apr 2007 23:17:04 +0100, Ben Blaukopf mused:

I know, which is why I doubted that the crimps would actually be in the kitchen, but who cares where they are anyway, as long as they connnected properly.

[Clive Mitchell]

In message , tony sayer writes

Page 974 paragraph 5.

"Only persons authorised by the government may hold an operational heat gun in the vicinity of a pudding joint, and only for as long as it takes to shrink the sleeve without melting all the rest of the plastic"

[John Rumm]

What brand of crimps are you using? Must admit to never having seen this happen before.

I take it you are running the wires insulation into the edge of the crimp so there is no visible ring of copper at the junction?

The other thing to do is to stagger the crimps (i.e. each wire a different length) so that they do not overlap. That also gives a neater join with less bulk.

[tony sayer]

SNB?..

Just wonder if that poxy part P affected this work or not as I'm being lumbered into doing the same..

Very, very, odd the original problem. Can you put up a photo or two of the joint for all to see?...

[Ben Blaukopf]

It's a cam.misc ref; you replied to my original post about Part P and Cambridge BCOs on cam.misc. What I meant was "Do I have to prefix every post I make with 'This work has been notified to the BCO'"

Since you ask, it alters a kitchen circuit, so yes it does come under it.

I'll take some photos of it when I strip it out - won't be till tomorrow evening.

Resistance is up from 43 ohms to 60 ohms after leaving it overnight.

Ben