Cable problems

[D Skelton]

So the other day I was installing downlights in a bungalow. Once they were installed on their own seperate circuit the two original lights were removed, cables pulled up and the loop in and out for each one crimped together. This was the only path in the radial for the first lighting circuit and yet the final two lights in the circuit wouldn't work. I traced the cable again, there was no visible damage along its entire length and it was definitly the mains feed for the final two lights so i guessed maybe one of the crimps was duff. I re-crimped both joins, even testing for voltage on both sides of each crimp before heat shrinking and they were sound, yet it still didnt work!? At this point I got fed up, ripped up the old cable and just layed a new one and all was fine. My question is whether it is possible for cables to corrode internaly? If not, what could have caused this problem? The original cable was the old style red/black PVC.

Secondly, just a quick one. Is installing a PIR security light on the outside of a house notifiable work under part P of the building regs?

 

[rocker]

A copper conductor can easily snap within the insulation and sheathing, especially 1 or 1.5mm that would be suitable for lighting.

Didn't you do any continuity and IR testing?

Yes, it is notifiable.

 

[D Skelton]

Yes, the first test I did was a continuity test and there was none, thats why i had to resort to changing both crimps and tracing the whole cable. The IR reading was fine tho???

 

[SMB]

You have answered your own question then.

A break in the cable.
(However, this don't happen very easily if its pvc/pvc, unless you sit and bend it at right angles repeatedly for 20 minutes, or unless its rubber or VIR).

The IR test would be fine....a break in a conductor, if its not shorted to another conductor, wouldnt show as a fault with an IR test.

Just out of curiosity...why are you using crimps and heat shrink in a bungalow loft rather than a junction box? I was just wondering likes.

Regards.

 

[D Skelton]

Yes, I understand that there will have been a break in the cable at some point along its length but I dont understand why as it was completely undisturbed other than at the points of entry into the old ceiling roses and at the crimps. I'm just very confused as to what could have possibly caused any damage??? Hmm, possibly just a very fragile cable. With regards to crimps haha, I completely understand why you ask. Don't ask why but if there is a way I can avoid using a JB I will as I hate them, they're like one of my pet hates. 99 times out of 100, if I have to join two cables I will crimp, even if I don't need to. I just feel better about it I guess.

 

[Marvo]

I agree corrosion is unlikely, most probably a manufacturing flaw or physical trauma to the cable from being accidentally compressed, hammered or pinched. We've had bad batches of cable before and got into the habit of continuity testing the 100m coils before they go to site.

 

[SMB]

Or even heat from within the light fittings you disconnected the cables from (not sure what type of fittings they were).

Was there much length on the cables when you re-connected them ? Were you able to strip the cables back much ?

Was there signs of heat?

T+E doesnt snap that easily.....until heat hits the equation.


I hope you didn't throw away the cable which caused you the problems because if you still have it then the problem will be able to be identified.

Go get the cable out of the skip and let us know when you identify the problem.

If it wasnt a problem with the cable it was a problem with termination.

Regards.


EDIT.....all that lovely lovely fibreglass insulation too. Don't you just love bungalows!?

 

[Marvo]

If the cable has gotten hot enough to damage the copper conductor then there would be visible evidence of this on the PVC insulation.

 

[D Skelton]

I'll be honest, the job took 6 hours longer than predicted due to a large number of problems that arose and weren't accounted for. Keeping the problem cable was the last thing on my mind when I was walking into the pub at 10pm instead of 5pm. Unfortunately it all got binned.

 

[SMB]

Tut Tut........no recycling?

All the best mate.

 

[D Skelton]

Haha, and you

 

[AcombAndy]

Secondly, just a quick one. Is installing a PIR security light on the outside of a house notifiable work under part P of the building regs?

Approved Document P. Page 9. Para i. Depends on a few things, I just read it the other day.

 

[D Skelton]

Depends on what exactly?

 

[jaresquire]

Generally, PIR type security lights are not a notifiable install unless they are fed from a new circuit or an addition to a special location circuit eg Kitchen.

 

[AcombAndy]

Very succinct 'The installation of equipment attached to the outside wall of a house (for example security lighting, air conditioning equipment and radon fans) is not notifiable provided that there are no exposed outdoor connections and the work does not involve the installation of a new circuit or the extension of a circuit in a kitchen or special location or associated with a special location'