Sorry i forgot why does this now change things?
Fault on existing lighting circuit
- Thread starter bobsmate
- Start date
Sorry i forgot why does this now change things?
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Can you tell me why you've wrote this and then when i've asked for a bit more advice as to how this would have changed things you then don't reply at all.
Bit confused by your description.
When you say split the cables - do you mean you split loop in/loop out then insulation resistance tested L/N/E on these cables separately?
If so, do you now get perfect readings on the L/N/E between the CU and the first light fitting?
Sorry about not being clear enough, yeah thats what i mean but i also seem to get perfect readings from the first light around the rest of the circuit then as well.
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So when i go back to the fault tomorrow then this should be what i check next?
It does indeed sound a little strange. But if the IR tests on the cables are all fine then not sure what else to suggest!
Despite this, i'm sure someone posted a problem with a lighting ciruit on here a while ago where a nail through a switch wire was causing periodic tripping under load but IR tests were fine. It was understandably a nightmare to locate.
Has the customer put any nails in the walls/shelves up etc?
It does indeed sound a little strange. But if the IR tests on the cables are all fine then not sure what else to suggest!
Despite this, i'm sure someone posted a problem with a lighting ciruit on here a while ago where a nail through a switch wire was causing periodic tripping under load but IR tests were fine. It was understandably a nightmare to locate.
Has the customer put any nails in the walls/shelves up etc?
Don't think he's put any shelves up but he has had a builder in insulating the walls and so they might have caught it then, i hope its not as it'll mean re-wiring the circuit. What is the mlikely hood of it being a faulty lamp or lamp holder?
Might be worth checking with the customer all the same - if not just to rule this problem out.
No idea. Are they standard ceiling pendants or more elaborate fittings of the finest Chinese manufacturing quality?
The problem is you say you have perfect IR readings with nothing connected in circuit. If you rewire the lighting circuit and put the old fittings back up you may have the same problem and I guess the customer would be none to happy to pay for the work?
I'm not sure how plausible it is to IR test light fittings - certainly not ones with transformers in.
Only other suggestion is putting up a load of pendant or double insualted fittings for a bit and seeing if the problem disappears? Not sure if this would work anyway!
Returning to your OP, what exactly was the fault that the customer was complaining of? Tripping RCD or MCB or some other problem?
Is this an upstair light circuit?
Does the wiring pass through the loft?
Is the loft boarded out?
Could a wire be trapped under a board?
How many lamps on the circuit / total load when all lights on?
Have you looked at all the wiring at each of the fittings connected to this circuit?
Is there any evidence of any melted insulation at any of these points?
Does sound a strange one, my guess based on a not too dissimilar situation is:-
One or more lamps cause a lot of heat at the fitting.
L/N or E insulation at fitting partially melted.
When cold, insulation is solid enough to give a good IR.
After a while in use, insulation warms up, due to current and heat from lamp.
Insulation softens.
Causes IR to drop.
Overload, fuse goes.
Is it possible for you to be there, switch lamps on, wait til fault occurs and quickly disconnect and test IR ?
Does the wiring pass through the loft?
Is the loft boarded out?
Could a wire be trapped under a board?
How many lamps on the circuit / total load when all lights on?
Have you looked at all the wiring at each of the fittings connected to this circuit?
Is there any evidence of any melted insulation at any of these points?
Does sound a strange one, my guess based on a not too dissimilar situation is:-
One or more lamps cause a lot of heat at the fitting.
L/N or E insulation at fitting partially melted.
When cold, insulation is solid enough to give a good IR.
After a while in use, insulation warms up, due to current and heat from lamp.
Insulation softens.
Causes IR to drop.
Overload, fuse goes.
Is it possible for you to be there, switch lamps on, wait til fault occurs and quickly disconnect and test IR ?
Not sure if this helps. Some time ago I went to a house which had been affected by an overflowing bath. Lighting circuit blowing fuse (old 5A Wylex). Checked all after drying out. No apparent problem and lights working. Left. Call again. Lights had worked for half an hour then the fuse had blown. Problem was an extractor fan FCU. When fuse pulled for testing IR then the fault was itself disconnected. Is there a fan on the lighting circuit? If so then the builders putting in insulation could easily have damaged the fan or its wiring. In a similar way, if a pin is loose in a bayonet fitting then removing the lamp will disconnect the fault and your IRs will be fine. If the householder had changed bulbs he could have used a little too much force on an old fitting. As mikhailfaradayski suggested the warmth from the lamp could be important, but here we're thinking that the actual pin or wire moves when warm. BTW: in the above problem, the fuse box had been boxed in at floor level and tracing was a pig; not helped by the activities of the burglar alarm fitter who had cut through the lighting circuit and used a double 13A socket as a junction box
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