Something strange

[a1guvner]

Hi all,

Thought i would throw this one out there,

Client has overhead supply coming into house and also has some outbuildings and requested a new supply from the DNO so he can have seperate bills for business use, i came along to fit a new dist board to the new supply, on this i fitted a split load board with 2 50 amp sub mains (existing) going out to the out buildings both with rcds upfront, when the installation was energised both rcds trip, so immediately you think got to be the neutrals on the wrong rcd, checked and all fine, turn on one supply and all fine turn on the other to the stable block and takes out both rcds even though they are going to different areas on the land and risk of a borrowed neutral somewhere is very slim,


anyone got any ideas why both rcds would trip

 

[malcolmsanford]

Are they new RCD's or like the sub main old existing ones?

If New could they be fauly? if old could they be faulty? Ramp test will tell.

It would seem that you may have a fault somewhere on that stable block, have you done any testing at all like IR. ?

When you say the DNO have supplied another supply, do you now have a 3 phase supply covering all installations or 2 x single phase supplies?

This to me seems you have a common neutral somewhere,and you have a fault that is being picked up on the neutral, possible N-E fault and therefore activating both RCD. which you would have on a 3 phase supply, and could also have even on 2 individual 230volt supplies as the DNO themselves may coupled them up.

It may even be something as stupid as wrong polarity somewhere.

 

[Knobhead]

Can we have a picture of the split load board?

 

[a1guvner]

All new rcds, ramp tested all fine, all the normal tests come back fine and they have single phase and the DNO has just taken another leg off the incoming overhead, to get the outside supplies back on we moved them both onto the same rcd and it holds fine

 

[a1guvner]

Can we have a picture of the split load board?

its a standard MK split load with MS feeding 2 rcds

 

[malcolmsanford]

Was there any load on the buildings when you switch on ?

On your original OP you stated the stable block when turned on takes out both RCDs, now you say if you connect up the both areas on to a singular RCD , I assume it's the stable and AN other, it holds?

Have you tried switching on one at a time? Have you tried the stable on each RCd alone and see what happens?

Is there anything in the stable that is likely to have had protective conductor currents when it was tripping both RCD, but could have then been off when you doubled onto a single one?

 

[a1guvner]

Was there any load on the buildings when you switch on ?

On your original OP you stated the stable block when turned on takes out both RCDs, now you say if you connect up the both areas on to a singular RCD , I assume it's the stable and AN other, it holds?

Have you tried switching on one at a time? Have you tried the stable on each RCd alone and see what happens?

Is there anything in the stable that is likely to have had protective conductor currents when it was tripping both RCD, but could have then been off when you doubled onto a single one?

They were only under minimal load, if you switch on rcd 1 first, holds fine, turn on rcd 2 both rcds trip, if you turn on rcd 2 first it holds fine and then turn on rcd 1 they both trip

 

[Knobhead]

I’m getting a horrible feeling I’ve seen this before, that’s why I asked for a picture.

 

[malcolmsanford]

The new board, the neutrals and RCD all correspond ok I assume. ?

Have the DNO crossed polarity ? It is sounding more and more like a polarity conflict.

 

[a1guvner]

I’m getting a horrible feeling I’ve seen this before, that’s why I asked for a picture.

that was my first thought and all the linking cables are definately going to the correct terminals, but i havent got any pics but there are other circuits on both sides which when they are on they hold fine

 

[malcolmsanford]

I think you have either reversed polarity somewhere or as you originally said, no matter how slim there is a neutral cross over somewhere

 

[a1guvner]

I think you have either reversed polarity somewhere or as you originally said, no matter how slim there is a neutral cross over somewhere

i think it has to be something like that

 

[Rockingit]

I'm reaching a bit here: Guess it's a TT site.... if you had a leakage fault on the main house, or on one of the two outbuildings, could it be the effect of two or more rods back-feeding that leakage current onto the new circuits????

Might be worth spending a few minutes with the leakage clamp out.

 

[tony mc]

What about energising the circuits one by one making sure the neutrals are taken out of each bar before putting that cct back on.

It should hold until you connect the offending neutral!

 

[a1guvner]

I'm reaching a bit here: Guess it's a TT site.... if you had a leakage fault on the main house, or on one of the two outbuildings, could it be the effect of two or more rods back-feeding that leakage current onto the new circuits????

Might be worth spending a few minutes with the leakage clamp out.

i did think about that as well, but now i have moved both the sub-mains back on to the same RCD if there was leakage i thought it would of raised the current and tripped again but it is holding fine