UK Rcd tripping cause?

[Ziggie]

Daughter’s new house.
Garage has very old wylex distribution box connected to a double socket and a lighting circuit with one neon.

put an RCD’ed extension cord in socket and the RCD trips instantly.
Measured leak current at main fuse area.
The neon light was switched off.
Leakages

house as is : 3.8 ma
House with garage distribution switched off 3.4 ma.
Using another circuit,extension cable 0ma

can use tools in socket without problem.

I think there is a fault in the distribution box in the garage.
seeking other opinions?

 

[Ziggie]

T

Some RCD will trip if the polarity is wrong (i.e. L and N swapped) or if there is no CPC (earth) connection. Both faults are very serious so it needs to be identified and fixed urgently!

You might be best to get a professional electrician in.

But if you feel you can (or want to) identify if it is the socket at fault or there is something odd with the RCD adaptor then you could try one of these:

TIS Socket Tester With Loop & RCD Check

A pocket sized checker for indicating loop impedance, socket polarity and RCD 30mA are all ok. Indication is by LED's and buzzer. An ideal unit for initial "checking out" of a 13A socket and will advise if the circuit is ok, needs attention, or needs urgent attention. An ideal product for...

www.toolstation.com

Please be aware that even these better quality socket testers are still limited in what they can tell you about the status of the supply socket. If they tell you it is faulty then you can be very sure it is, however, if they give the all-clear you might still have some subtle faults present. The cheap ~£10 socket testers are not that good though as they will pass a socket with wet string for the CPC!

Thanks to all

 

[Ziggie]

Apologies to all.

I decided to use my socket tester ….. as I couldn’t remember checking the garage (oops).
It showed 1green meaning L and N wrong way round.
I checked with my loop impedance and it failed to start reporting a phase error.
Looking in the socket- there is one red, one black and a bare wire covered in black screening.
In the fuse box, there is the same mixture of wires.
The wires

 

[Ziggie]

So now for the approach given the wires are the wrong way around.
The layout is
Main CU
Fused spur kitchen
Fuse box garage
Socket
We know wires are crossed but what is the easiest may of finding where it occurs.
(As I stated there’s lots of black wires ( also in t&e)
The only method is to label all and disconnect
Check continuity to identify ends of each wire.
Then rewire the lot

must be an easier way? Suggestions welcomed!

 

[Mikegh]

Probably start in the middle somewhere and find it with a voltstick then confirm

If that's what you're saying?

You've got reverse polarity at an outlet and you don't know where it originates

 

[Mikegh]

Sorry haven't really been following the thread

 

[Dave OCD]

I would also double check that the black insulated core was connected to neutral at both ends and the bare conductor with bodged black sleeving is connected to earth - and also replace with correct green/yellow sleeving.

 

[Ziggie]

I would also double check that the black insulated core was connected to neutral at both ends and the bare conductor with bodged black sleeving is connected to earth - and also replace with correct green/yellow sleeving.

Thanks - yes I want to replace sleeving once I find the cross over.
I’ve decided to draw it all out on paper as a first step!

 

[Ziggie]

Probably start in the middle somewhere and find it with a voltstick then confirm

If that's what you're saying?

You've got reverse polarity at an outlet and you don't know where it originates

Yes I’ve got socket tester reporting L and N reversed and a rcd tripping implying L to E somewhere.The socket is at the last stage of socket - fuse box. - fused spur - main CU.

 

[Mikegh]

Yes I’ve got socket tester reporting L and N reversed and a rcd tripping implying L to E somewhere.The socket is at the last stage of socket - fuse box. - fused spur - main CU.

You'll probably need to IR test so, as well as find the reverse polarity

 

[telectrix]

wander lead would be useful here. can make up a temp. one with a length of scrap single.