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Struggling to find anything obvious on the cabling I can examine. There are some crappy joins (no earth sleeving used in places and wires twisted tight against each other) thought I may have found where a non sleeved earth has almost worn through the neutral insulation but separating them has made no difference.
Am wondering whether it will be quicker to run new cable round. Looks like they have used about 10ft of 2.5mm2 from the db and then randomly joined it to about 160ft of 1mm2 to the switch joined the neutrals there and then run the cable to light unit 1 from there to light unit 2 etc up to the sixth light.
I can see the order the lights are wired so I guess I could disconnect them one at a time (furthest away to nearest switch) to rule the cable to each one out.
The trip almost never goes straight away - sometimes takes 15 mins or so.
Am wondering whether it will be quicker to run new cable round. Looks like they have used about 10ft of 2.5mm2 from the db and then randomly joined it to about 160ft of 1mm2 to the switch joined the neutrals there and then run the cable to light unit 1 from there to light unit 2 etc up to the sixth light.
I can see the order the lights are wired so I guess I could disconnect them one at a time (furthest away to nearest switch) to rule the cable to each one out.
The trip almost never goes straight away - sometimes takes 15 mins or so.
Dave-sparks
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It sounds like the whole circuit is a mess that could do with being replaced.
brightspark
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its my bread and butter
love fault finding had 3 last week/ beats doing hard graftDo I seem to be on the right track? It can only be this cable run to the switch now I think.
Dave - from what I can see the lights look ok. My suspicion is that the previous owner ran the supply to the switch and someone else wired them up. So if I am on the right path I will just replace the supply to the switch.
Dave - from what I can see the lights look ok. My suspicion is that the previous owner ran the supply to the switch and someone else wired them up. So if I am on the right path I will just replace the supply to the switch.
brightspark
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its not a dead short to earth and only trips when something else in circuit is used
brightspark
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cant realy say without testing with an insulation tester and parting the cables 
I get that they are connected and that I cant isolate them other than by disconnecting them at the DB but am struggling to get a scenario in my head!
If I turn the MCB off to this supply to the lights, I cut the live only and it doesn't trip. Then I disconnect that same wire and isolate L,N &E where it was connected to the switch and it will trip if the MCB is left on. Doesn't that all point to that cable on that circuit? So will running a new supply for the lights solve the issue or just half of the problem? From what you and BS say it sounds like another circuit must be involved but I cant work out why.
(Sorry if this is a dumb question, just trying to understand, not argue! Appreciate the help a lot!)
If I turn the MCB off to this supply to the lights, I cut the live only and it doesn't trip. Then I disconnect that same wire and isolate L,N &E where it was connected to the switch and it will trip if the MCB is left on. Doesn't that all point to that cable on that circuit? So will running a new supply for the lights solve the issue or just half of the problem? From what you and BS say it sounds like another circuit must be involved but I cant work out why.
(Sorry if this is a dumb question, just trying to understand, not argue! Appreciate the help a lot!)
dobbslc
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That cable to the light switch might well be at fault so it's worth testing that with a meter if you can.
Sometimes you can get a build up of fault current from various different circuits that may be just under the 30ma threshold of that RCD, but turning on the lights will add a bit more fault current that will take the fault current over the RCD trip current making you think you've found the fault.
You can check this by turning off all the circuits then turning them on one at a time STARTING with the lighting, if it trips straight away you've probably found the fault but if it trips when you turn on the last couple of circuits then you have something else going on.
Here's a technical drawing
any 3 circuits being on won't trip the RCD but a combination of 3 or 4 of the them will.
So depending on what order you switch stuff on can make you think the last one is the faulty circuit, turn them on in a different order can make it look like a different one!
This is why sparks should always be paid more than plumbers, as it's easy to find a leaking pipe
Sometimes you can get a build up of fault current from various different circuits that may be just under the 30ma threshold of that RCD, but turning on the lights will add a bit more fault current that will take the fault current over the RCD trip current making you think you've found the fault.
You can check this by turning off all the circuits then turning them on one at a time STARTING with the lighting, if it trips straight away you've probably found the fault but if it trips when you turn on the last couple of circuits then you have something else going on.
Here's a technical drawing
any 3 circuits being on won't trip the RCD but a combination of 3 or 4 of the them will.
So depending on what order you switch stuff on can make you think the last one is the faulty circuit, turn them on in a different order can make it look like a different one! This is why sparks should always be paid more than plumbers, as it's easy to find a leaking pipe
Ah, Got it.
So the odd thing here is that the cable supplying the lights is now just a cable - the lights are disconnected. So it runs from the DB and then I have disconnected and terminated it at the switch. The trip only blows when that cable has a live feed to it (by turning the MCB on) even though it now doesn't supply anything - nothing should be connected to it. I will open up all of the trunking so I can examine it along its entire length to make sure someone hasn't 'tapped' into it for an earth or something somewhere else.
So the odd thing here is that the cable supplying the lights is now just a cable - the lights are disconnected. So it runs from the DB and then I have disconnected and terminated it at the switch. The trip only blows when that cable has a live feed to it (by turning the MCB on) even though it now doesn't supply anything - nothing should be connected to it. I will open up all of the trunking so I can examine it along its entire length to make sure someone hasn't 'tapped' into it for an earth or something somewhere else.
I have and was!! :-)
So, interestingly there are no other joins on the wire I can expose other than this one I described above where they have run the 2.5mm (?) on the right from the DB ten feet to here and then joined to what looks like 1mm on the left. No earth sleeving but the wires are secure. It was rammed in the trunking fairly tight.
I have pulled that out and its not touching anything.
Now i have pulled the cable about the trip is going consistently every time i turn the MCB to this cable on.
At the end of the trunking the cable disappears into a roof void that I cant access. (Am too wide to fit and it wont take my weight!) I cant examine it there.
At the point it goes into the roof void? Would have to cut it there.
Cable is badly routed through a metal panel and this needs rectifying. But the light supply doesn't look visibly damaged. It has an odd twist to it though (first photo).
Only two of those are live. The pipe was for a compressor. The metal wall has cut the outer case on the armoured cable (this is live 3phase).
Cable is badly routed through a metal panel and this needs rectifying. But the light supply doesn't look visibly damaged. It has an odd twist to it though (first photo).
Only two of those are live. The pipe was for a compressor. The metal wall has cut the outer case on the armoured cable (this is live 3phase).
