Nightmare fault!!

[highspark]

Done a board change today.

Kitchen Sockets on RCD1, Up sockets on RCD2. Both rings.

When energised RCD1 tripped. When I removed the neutral of the Up sockets on RCD2, the Kitchen Ring & RCD1 did not trip. As soon as I put neutrals back in on RCD2 side. RCD1 trips.

Thought there may be a borrowed neutral or got legs mixed up, so decided to put both circuits on the same RCD and neutral bar. Still Tripped!

Removed all appliances from Circuits - still tripped.

Next replaced both RCD's still tripped. Scratching my head off!!

its a hard one to explain. Basically when all conductors of both rings are connected the RCD just trips. If I remove the up sockets completely the kitchen sockets are fine and vice versa! It's only when all conductors are connected!!

Is is there an interconnection somewhere between these two circuits?

the only work they've had carried out is a new kitchen 4 years ago and a new boiler with a y plan system 3 years ago. I'm guessing there's been an interconnection made at those times!

 

[telectrix]

so test between all 3 of the conductors of RFC1 to those of RFC2. with all cables dissed from CU a 500V IR test should show up the problem.

 

[davesparks]

This old chestnut again?

I'm going to hazard a guess that you didn't carry out the standard insulation resistance tests before switching on?

 

[Bobster]

SO rather than actually testing anything, you just started swapping things around hoping it would work?

 

[Octopus]

So with all the legs into the same MCB's & RCD it trips, yet remove either of the pairs and its OK, hum..........

 

[Knobhead]

More to the point, did you test before installing the board?

I doubt it very much.

This record is wearing thin.

 

[midgetman]

Sounds like more than 1 fault. Get tester out buddy

 

[davesparks]

Sounds like more than 1 fault. Get tester out buddy

How have you drawn that conclusion?

The symptoms described are exactly what you'd expect from one of the most common faults encountered when changing old CUs.
And which any electrician should be able to work out in pretty short time.
And it has been discussed many many times on this forum so a quick search should have answered this!

 

[midgetman]

Cos I am a muppet

 

[GMES]

And the hits just keep on coming!
Op why are swapping stuff out to try to find a fault! get your bloody test equipment out and use it.
Do you carry 2 of everything in your van because you don't know how to test.
If the above advice sounds Harsh, then read your post back to yourself, at no stage did you suggest that you have even attempted to test any circuits.
Sadly the Bang test is over rated.

 

[Redvanman]

I had a call out not so long ago, both RCDs tripping didnt seem to be any particular circuit or RCD.
Out can the tester found N to E fault on a ring spent good half hour taking all the fronts off and testing between until very last one had the screw thro neutral.
The socket front was new one so asked client who had put it on.
His reply was "me earlier but didnt think that could have caused it" ARGGGG
Didnt think to tell me when i turned up.
Dont you just love em!!!!!!!!

 

[davesparks]

Why take all of the fronts off?
Split the ring in half, identify faulty half, split that half in half......

This is the basic logical process for tracing faults in circuits, no need to go taking everything apart!

 

[Octopus]

I had a call out not so long ago, both RCDs tripping didnt seem to be any particular circuit or RCD.
Out can the tester found N to E fault on a ring spent good half hour taking all the fronts off and testing between until very last one had the screw thro neutral.
The socket front was new one so asked client who had put it on.
His reply was "me earlier but didnt think that could have caused it" ARGGGG
Didnt think to tell me when i turned up.
Dont you just love em!!!!!!!!

With RCD tripping I always ask if ANY diy has been done or water leaks have been noticed - when I say it may help track down the fault AND save them money their memories suddenly become clear!

 

[HappyHippyDad]

Done a board change today.

Kitchen Sockets on RCD1, Up sockets on RCD2. Both rings.

When energised RCD1 tripped. When I removed the neutral of the Up sockets on RCD2, the Kitchen Ring & RCD1 did not trip. As soon as I put neutrals back in on RCD2 side. RCD1 trips.

Thought there may be a borrowed neutral or got legs mixed up, so decided to put both circuits on the same RCD and neutral bar. Still Tripped!

Removed all appliances from Circuits - still tripped.

Next replaced both RCD's still tripped. Scratching my head off!!

its a hard one to explain. Basically when all conductors of both rings are connected the RCD just trips. If I remove the up sockets completely the kitchen sockets are fine and vice versa! It's only when all conductors are connected!!

Is is there an interconnection somewhere between these two circuits?

the only work they've had carried out is a new kitchen 4 years ago and a new boiler with a y plan system 3 years ago. I'm guessing there's been an interconnection made at those times!

If there is, then a continuity test would tell you in seconds HighSpark!

I made the same mistake sometime back (not testing before changing a CU)... got a right kicking on the forum and didn't do it again! Although I have to admit if it is a borrowed neutral this isn't going to show up in any of the 'usual' pre-tests!

Heres a couple of links that might be useful:

http://www.electriciansforums.co.uk...ctrical-regulations/12971-cu-changes-you.html

View attachment CU check list open in word.doc

 

[Redvanman]

With RCD tripping I always ask if ANY diy has been done or water leaks have been noticed - when I say it may help track down the fault AND save them money their memories suddenly become clear!

Your right but i think i was in the frame of mind that he would have told me.

Never trust them, never trust them

 

[SPARTYKUS]

Why take all of the fronts off?
Split the ring in half, identify faulty half, split that half in half......

This is the basic logical process for tracing faults in circuits, no need to go taking everything apart!

thats just so boring though.

its far more exciting redvanmans way (I'm a bit tongue in cheek but also slightly serious....:biggrinjester::biggrinjester

it is more exciting though isn't it?

 

[HappyHippyDad]

thats just so boring though.

its far more exciting redvanmans way (I'm a bit tongue in cheek but also slightly serious....:biggrinjester::biggrinjester

it is more exciting though isn't it?

Thats because you're Mr Mischief! :biggrinjester:

 

[SPARTYKUS]

I prefer mr coma.

 

[uksparks]

I don't know the bloke so won't be rude, but I agree, I doubt very much that he tested it to death before changing it.

I just cannot understand why people do this, I would never dream of doing it because I can be you there will be a nest of problems.

If this had been tested first properly then this situation would not have arisen.

 

[HappyHippyDad]

I don't know the bloke so won't be rude, but I agree, I doubt very much that he tested it to death before changing it.

I just cannot understand why people do this, I would never dream of doing it because I can be you there will be a nest of problems.

If this had been tested first properly then this situation would not have arisen.

But would you have tested all the neutrals with each other for continuity to see if there was a borrowed neutral UK?

ps.. before the change.