NEWBIE HELP! RCD tripping is doing my head in...

[zipbung]

Just had a brand new 16th Edition board put in. When it first went in the RCD test button didn't work which was odd.

I have...

Upstairs lights.
Downstairs lights.
Smoke detectors.
Kitchen ring.
Upstairs ring.
Downstairs ring.

Now we have tested each one (example downstairs lights) and the first light goes on ok, then subsequent lights trip the rcd. If all lights are off and then say the kitchen lights go on that trips it as well. Also, I can turn off the kitchen lights, reset the RCD and turn the kitchen on again and it doesn't trip the RCD.

The same is for all rings in the house. I presume it is unlikely that all rings have the same wiring problem (neutral/earth etc), am I right in thinking it is a faulty RCD and all I need to do is swap it out?

Could there be any other reasons?

Help me DIY'ers, you're my only hope...

 

[SparkyNinja]

Who carried out the work?

 

[zipbung]

It was a local qualified electrician (not me) but had a run in so can't go back there sadly , so I have another guy in now who knows his stuff and will try to swap the RCD for a new one tomorrow to see if that's it.

If it's not that - its a wiring fault right?

 

[ColJack]

sounds like either a faulty RCD, or the neutrals are in the wrong bar...
if you can get us an in focus picture of inside the CU with the cover off we can see if there might be a problem in there..

why the run in?
let me guess you tried to stiff him on part of the bill?

 

[SparkyNinja]

The fact that a light works, then switching on another like you explained makes it trip may be a neutral being borrowed,but a picture would be very helpful as ColJack explained


If the RCD test button didn't work when it was installed then it should have been replaced anyway.

 

[zipbung]

Will try to get photo up asap, what does borrowed mean - does it mean the wiring under the floorboards is bad, or that the wires on the board itself have been misplaced (childhood...)?

 

[ColJack]

borrowed neutral means that the live from one circuit is comming back do wn the neutral of another..

as this is a "16th edition cu", and from the description you gave, it sounds like you only have one RCD and not RCBO's?

are the lights on the rcd side or not?

 

[SparkyNinja]

Will try to get photo up asap, what does borrowed mean - does it mean the wiring under the floorboards is bad, or that the wires on the board itself have been misplaced (childhood...)?

It may mean nothing at this stage. Was there an RCD installed before?.

I had this scenario last week where I installed a 17th edition DB and split the lights across two RCD's. But because of the borrowed neutral the second the lights was switched on that uses the borrowed neutral it tripped.

However this may not apply to you, a pic would be better

 

[zipbung]

Yes its a 16th ed CED cu, the lights are now on the right hand side (non RCD side I understand) so we can get the lights on (I'm not living in he property yet) and the kitchen ring so we can fire the boiler up tomorrow and see if we have to get cold showers (I need one after today)...

Not sure what RCBO's are?

 

[zipbung]

Thanks Widdler - yes the board we took out was about 20 odd years old and had no RCD's (think it was mice that powered the bugger - there were plenty of droppings in the cupboard like)...

 

[SparkyNinja]

Thanks Widdler - yes the board we took out was about 20 odd years old and had no RCD's (think it was mice that powered the b*****r - there were plenty of droppings in the cupboard like)...

Did the electrician carry out any testing and provide you with any information about your existing installation?

There may be damage to some cabling if you have found droppings.

 

[zipbung]

Just joshing about the mice (old kit - bad joke - sorry).

I was there when he tested the rings (I recall he twisted the blue and brown wire (I think) and put his Fluke thingy on each socket (I think) and it bleeped each time.

Bit vague, but it's been a long week...

 

[SparkyNinja]

I was there when he tested the rings (I recall he twisted the blue and brown wire (I think) and put his Fluke thingy on each socket (I think) and it bleeped each time.

OK

Did you get any paperwork?

 

[Goldberg]

sounds like either a faulty RCD...

I concur.

...or the neutrals are in the wrong bar...

How can neutrals in the wrong bar cause an intermittent imbalance?

if you can get us an in focus picture of inside the CU with the cover off we can see if there might be a problem in there..

How many times have you seen a problem inside a CU cause an intermittent imbalance?

borrowed neutral means that the live from one circuit is comming back down the neutral of another.

That's somewhat misleading. A borrowed neutral is a connection between two otherwise indepedant circuits. It's invariably an unlabelled situation, therefore particularly unsafe, not least because each of the two affected circuits doesn't have a single point of isolation.

How can a borrowed neutral on a 16th CU (i.e. without RCBOs) cause an intermittent imbalance?


zipbung - does the RCD trip if you unplug all appliances and turn off all fixed load DP switches (cooker, hob, immersion)?

If so, do you have equipment capable of carrying out an insulation resistance test?

 

[Chri5]

When you say 16th, do you not mean 17th ed spec which is a requirement since July 08 ?

If 17th, does the board have 2 x RCD's ?

And if so the lighting circuits should be split across different RCD rails to avoid a single point of failure (all lights failing if 1 x RCD trips).

If the RCD isn't knackered (having tried a new unit) the likelihood is that one of the lighting circuit neutrals is not on the correct neutral bar- on a 17th install with 2 RCD's the neutral MUST go on the correct neutral.

As for intermittent, please confirm if this fault happens occasionally or does it happen all the time ?