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

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

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?!

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.
--
Regards,
Stuart.

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

Also heating it up won't help the minimal amounts of insulation left.
--
Regards,
Stuart.

In article , Lurch
writes
On Sun, 15 Apr 2007 20:15:03 +0100, Lurch
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.

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

Where's part Pee come into this?...
--
Tony Sayer

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

In article , Lurch
writes
On Sun, 15 Apr 2007 20:15:03 +0100, Lurch
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.

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

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

Dunno. Why should part p be an issue?
--
Regards,
Stuart.

In article , Lurch
writes
On Sun, 15 Apr 2007 21:19:37 +0100, tony sayer
mused:

In article , Lurch
writes
On Sun, 15 Apr 2007 20:15:03 +0100, Lurch
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.

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

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

Dunno. Why should part p be an issue?


Electrix in a Kitchen?....
--
Tony Sayer

In message , tony sayer
writes
Also heating it up won't help the minimal amounts of insulation left.

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

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"


--
Clive Mitchell
http://www.bigclive.com

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

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?!

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.

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

Ben

Ben Blaukopf wrote:

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

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.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

John Rumm wrote:
Ben Blaukopf wrote:

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

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

Screwfix. They might have a label on, but I'm upstairs with whisky and
can't be bothered going down!

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?

yes


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.

They are staggered. There is a small bit of overlap though.

Ben

Ben Blaukopf wrote:

Screwfix. They might have a label on, but I'm upstairs with whisky and
can't be bothered going down!

Not tried them, so can't comment... Usually get mine from CPC.

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?

yes

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.

They are staggered. There is a small bit of overlap though.

Sounds like losing the overlap would help.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

In message , Ben Blaukopf
writes
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?!

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

--
Clive Mitchell
http://www.bigclive.com

Clive Mitchell wrote:
In message , Ben Blaukopf
writes
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?!

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


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

Ben

It's not a dead short - it's 43ohms.

Fit a heatsink and let it dissipate 1.5KW

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

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


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

wrote:
It's not a dead short - it's 43ohms.

Fit a heatsink and let it dissipate 1.5KW


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.

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

Finally got round to another look at this, and it took me two minutes
before I realised...

Totally my fault. Complete and utter loss of brain. I'm an idiot.

I've been doing lots of work on the kitchen ring main. Which is RCD
protected. The lights circuit obviously isn't, I wasn't testing it at
the CU, I was just doing a quick sanity check before energising. So I
carefully measured the resistance of a lightbulb and the path thence
back to the earth-neutral bond in the cut-out. And yes, I can only
assume I was measuring it with the switch turned on, because I was
testing live, not switched live.

So while my wiring was fine, I'm currently doubting my competence to
wield a screwdriver....


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,

Clearly the "no short" bit was me not testing well enough.