Nightmare of a day. RCD tripiing under any load

[brizospark]

Have had one of them days. I had a board change to do and a few other bits and bobs so everything was going great until I tried to put power back on.

Basically I have replaced a 3036 board with a split load Wylex board. One half of the board is working fine but the other half's RCD is tripping as soon as anything is plugged into it.

If I remove all plugs from sockets then the RCD holds but as soon as I plug anything in, kettle, sky box, TV, it trips instantly. On this side of the board is the cooker, 1 x lighting circuit and 2 x ring mains, funny enough the RCD isn't tripping when the lighting circuit or cooker is on.

Now I have checked that I have neutrals from correct circuits going to the correct neutral bar, several times and these are OK. I tried replacing the RCD itself with the one that was OK and it still tripped. What else is strange is that the kitchen ring is on the side of the board which is fine but if I plug anything into a kitchen socket the RCD which isnt even protecting this is tripping!! I opened up sockets and everything looked OK but it was getting late on so I replaced the offending RCD with a main switch I had in van just so the couple have power on tonight before I go back again tomorrow. Switched on with RCD removed and everything fine.

Anyone had experience with this problem before? Any advice much appreciated

 

[sima24]

Sounds like borrowed neutral to me. Have u tried putting the 2 lighting circuits on the same rcd?

 

[sima24]

Has it been tested to rule anything else out?

 

[Brightspark2]

Everything test out ok?...


Borrowed neutral?....or shared neutral whatever you want to call it.

 

[Marvo]

With a borrowed neutral, shared neutral or split neutral or whatever you call it the RCD won't trip until there's some current flowing. If there's no load current then there's no fault current so it will hold if you unplug everything and turn all the lights off.

Rather than using the RCD to do your fault finding use your normal tester and your mega tester if necessary.

 

[trev]

It could also be a neutral to earth fault but your IR testing ruled that out. Right?

 

[Dizzy_Maskell]

Yes sounds like to me like a borrowed neutral. Have they had extensions done you will need to break each circuit up and test in stages some where some one had tapped into a neutral or you could try try putting all socket circuits on one side of the RCD

 

[brizospark]

Thanks for replies guys yes everything tested out ok. So we are looking at a borrowed neutral most likely then?

 

[sledgehammer]

Neutral to earth fault, megger out.

 

[i=p/u]

Test before touch

 

[sledgehammer]

Sorry should've said, shows its self as you try to draw power. As you said its as soon as you plug in and use power.

 

[wersolaruk]

Sounds like a existing fault somewhere on wiring I.e nipped cable in box etc creating a existing fault on system once all the appliances are plugged in could just be cresting enough leakage to trip rcd. Had that one before, customer had used a 16mm back box whilst adding a new socket in kiddies bedroom!!! and cables were pushed against it! I came along changed d.b and found the fault 5 hours later! Pulling my hair out!

 

[trev]

It's either N-E fault in which case a simple global test will show it up and you can narrow it down to a circuit from there or it's a borrowed neutral, in which case a simple test will show it up.
Borrowed neutrals are usually on the landing light in my experience, should be an easy one to sort mate.

 

[brizospark]

What's confusing me is why when I plug anything into kitchen socket covered by RCD A is it tripping RCD B? Surely this means it can't be a N to E fault as it would trip RCD B if this was the case

 

[brizospark]

Can anyone explain that?

 

[SJD]

I'd also suggest neutral to earth fault somewhere, and not necessarily on the circuits on the problematic RCD.

 

[sledgehammer]

If its pme n-earth fault would common out both neutrals. I've had had exactly what you're talking about many times and its n-e.

 

[wersolaruk]

Could there be a borrowed neutral at that kitchen socket itself. Turn the rcd off covering that socket and turn other rcd on. Test between n-e at the problematic socket and if its showing voltage to earth it's a borrowed neutral! Sounds like a fault I would love to find!

 

[Brightspark2]

If its pme n-earth fault would common out both neutrals. I've had had exactly what you're talking about many times and its n-e.

Nice avatar :smartass2:....

 

[brizospark]

Could there be a borrowed neutral at that kitchen socket itself. Turn the rcd off covering that socket and turn other rcd on. Test between n-e at the problematic socket and if its showing voltage to earth it's a borrowed neutral! Sounds like a fault I would love to find!

It's not just this kitchen socket it is any socket in house covered by either RCD