Help ! Lights tripping RCD after consumer unit change.

[sidekick]

Have done a consumer unit change and after finding and resolving all other faults I am now pulling my hair over this one.

Landing Lights when switched on trip the RCD.
Originally placed light circuits on different RCD's and tripped,
put all light circuits on same RCD and still tripped,
have now put every circuit on same RCD and stiil trips.

Have checked all accessible accesories and connections but unable to get into any ceiling or under any floor, can find nothing wrong. How do I find the fault (taken three days to do this job and no idea how to find the fault now) Could I have got a wire wrong on the consumer ghange. The rewireable fuse and now MCB has two lines, two neutrals and two earths.

 

[malcolmsanford]

When you say you put all the circuits on the one RCD did you also put all the neutrals on that RCD bar or did you have them spread still over on the 2 bars.

As this is a landing light scenario I would say 90% that you have a borrowed neutral.

 

[sidekick]

When you say you put all the circuits on the one RCD did you also put all the neutrals on that RCD bar or did you have them spread still over on the 2 bars.

As this is a landing light scenario I would say 90% that you have a borrowed neutral.

Thanks. All neutrals on same bar. Have come accross borrowed neutrals several times in past on landing lights so think able to rule that one out.

 

[telectrix]

once again malcolm beats me to it. damn and blast. but i'll raise the bid to 95%

 

[malcolmsanford]

Have done a consumer unit change and after finding and resolving all other faults I am now pulling my hair over this one.

Landing Lights when switched on trip the RCD.
Originally placed light circuits on different RCD's and tripped,
put all light circuits on same RCD and still tripped,
have now put every circuit on same RCD and stiil trips.

Have checked all accessible accesories and connections but unable to get into any ceiling or under any floor, can find nothing wrong. How do I find the fault (taken three days to do this job and no idea how to find the fault now) Could I have got a wire wrong on the consumer ghange. The rewireable fuse and now MCB has two lines, two neutrals and two earths.

Not sure what you mean by that.

Well if it is not a borrowed neutral as you say, and I assume you have done IR on each circuit and all was ok then the common denominator is the 2 RCD's and perhaps you may have a bad batch.

Try a ramp test on each to see what you get, and then perhaps fit another one that you know is ok

 

[sidekick]

Maybe a borrowed neutral here. As was posted on a thread here recently do an IR test between both neutral bars at 250V: should be a resistance there if flat then there may be a borrowed neutral. Do an IR test on the whole install n all...maybe an insulation problem here.........

All neutrals on one bar now but tried that before I moved them. with light circuits removed got >2000 with light circuit connected got low reading (can't recall value now). So moved all. Any idea what I can do next ??

The old fuse did have 2 lines with 2 neutrals and 2 earths so have left same in new mcb - still trips

 

[DNS1]

with light circuits removed got >2000 with light circuit connected got low reading (can't recall value now).

You mean you got a low IR value with the lighting circuit connected?

Have you tested the IR of the lighting circuit alone (disconnected completely from the consumer unit)

 

[DNS1]

Hope my questions aren't too stupid by the way, as I've said on a couple of threads I'm pretty new to this, but trying to help with other people's problems is a great learning experience.

 

[sidekick]

Hope my questions aren't too stupid by the way, as I've said on a couple of threads I'm pretty new to this, but trying to help with other people's problems is a great learning experience.

All helps and is appreciated. I did get low IR between neutral bars before I moved all circuits onto 1.
Did IR on light circuit disconnected but with L+N together to E to avoid removing millions of down lights on same circuit and read 127 mohms

 

[sidekick]

Not sure what you mean by that.

Well if it is not a borrowed neutral as you say, and I assume you have done IR on each circuit and all was ok then the common denominator is the 2 RCD's and perhaps you may have a bad batch.

Try a ramp test on each to see what you get, and then perhaps fit another one that you know is ok

With light circuit removed all RCD trip times on rings etc now ok. Also ok when light circuit connected as long as landing light not switched.

 

[telectrix]

got to be the landing light then. find out where it's line feed comes from. if it's fed in from the downstairs circuit, that's your problem. if not, check fitting and switches.

could be a L trapped with faceplate screw.

 

[SimpleSimon]

Theres your borrowed neutral hopefully.

But if you've said you've put both on one RCD than....maybe not?

Going back to IR tests, take the neutrals only from each light circuit and test between these.

 

[sidekick]

got to be the landing light then. find out where it's line feed comes from. if it's fed in from the downstairs circuit, that's your problem. if not, check fitting and switches.

could be a L trapped with faceplate screw.

Checked all landing light connections and both switches even tried with all hanging off just in case any trapped or nicked and still tripped but nothing found. Don't suppose another light working ok would cause trip when landing light switched.
This seriously has me baffled.

Quick sketch added. Not much to go on but all I have been able to access. 2 way switches missed but wired as should be

 

[C4rlosuk]

Disconnect landing switch line from light, re test ir on circuit at ccu if all now clear then I would remove both switches (if 2way) and carry out ir on all conductors and replace what ever cable shows bad.Ive had faults on switch lines many times some due to water in switch others caught cables but most of all is silly beggars sticking nails in for pictures. LolHope you get your problem sorted.

 

[sidekick]

Just to add insult to injury. Customr now thinks I have taken too long and wants me to put lights on unprotected by rcd circuit. Oh Boy!