RCD tripping weird

[aaelectric]

Went to a job today where the RCD was tripping.
everytime you turn on fridge or freezer it trips. Then on the other side that is not RCD protected the kitchen lights trip the RCD when turned on. It's newish install couple of years. The RCD trips even when the RCD side bus bar is off and the kitchen lights are turned on. I tested the RCD at half which was ok no trip, tested at 1 there was not trip tested at 5 triped 10ms so it's not tripping at 1x. It's weird how the lights on the non RCD side trips the RCD I tested between the two neutral bars and there is no continuity. There is not another lighting circuit on the RCD side. What do you think, the fridge and freezer carnt both be faulty and kitchen lights, do you reckon RCD but it stays up with all other circuits?..
cheers in advance

 

[rich.250]

Sounds like a borrowed neutral from
The non rcd side, creating an imbalance between line and neutral

 

[MarkieSparkie]

Went to a job today where the RCD was tripping.
everytime you turn on fridge or freezer it trips. Then on the other side that is not RCD protected the kitchen lights trip the RCD when turned on. It's newish install couple of years. The RCD trips even when the RCD side bus bar is off and the kitchen lights are turned on. I tested the RCD at half which was ok no trip, tested at 1 there was not trip tested at 5 triped 10ms so it's not tripping at 1x. It's weird how the lights on the non RCD side trips the RCD I tested between the two neutral bars and there is no continuity. There is not another lighting circuit on the RCD side. What do you think, the fridge and freezer carnt both be faulty and kitchen lights, do you reckon RCD but it stays up with all other circuits?..
cheers in advance

When say "The RCD trips even when the RCD side bus bar is off ..." do you mean by this that you have isolated the final circuits connected to RCD by switching OFF their respective MCBs or have I misunderstood you?

 

[Hawk81]

Sounds to me like a borrowed neutral on the lights and a faulty RCD.

 

[mickys86]

It does sound like a borrowed neutral, but even if you isolate the mcb's on the RCD side it will still trip the RCD if there is a problem. Try disconnecting the earths and replace them one by one. If there is a problem with the circuit then the RCD will trip out. (RCD on but all other mcb's off!!)

 

[TaffyDuck]

I have come across this scenario before. Or at least something similar with a hob tripping the other side RCD on a dual RCD board. Firstly ramp test the RCD. Trip times are not that relevant in this instance but the actual mA that is introduced by your tester is. Firstly turn off all the circuits at the MCBs and test the RCD at the board. A 30ma RCD will typically trip at between 23 and 27mA of induced fault current. Next individually turn on the circuits and carry on testing the RCD at the board. If you get a significant drop in the amount of current the tester has to introduce to trip the RCD when you turn on a particular circuit then that circuit, or an appliance using it is suspect. When I came across this in an old stone farmhouse I freely admit I scrat ched my head for a while. Even talked the the techies at my ECA. Their answer was well RCDs act strangely sometimes, who knows which was no help at all.

 

[TaffyDuck]

A borrowed neutral by the way would have always tripped the board so unless work has been carried out recently thats unlikely to be the answer

 

[keefy]

Had a few wierd ones like this, posted one recently. What I have found is that if you get 'wierd' tripping of RCD, IR N-E. A few times now, about 4 if I can count right, it has been no more than poor distance, or short between neutral and earth. It's so easy to start looking for other things, a borrowed neutral possibly, but if it's an existing installation who recently borrowed it?

 

[aaelectric]

Exactlyno work has been done recently. As I said I tested between neutral bars and there is no continuity which would indicate no borrowed neutral. As I said I had taken the bus bar from the RCD out turned on and turned the lighting circuit on the non RCD side and it trips RCD

 

[aaelectric]

I even moved the lighting circuit onto the RCD side and it still tripped

 

[TaffyDuck]

Have you ramp tested the RCD, Ive found that when they get below about 19mA they get very wierd. Might also be worth trying a 100mA just to give you an idea how big the fault is. Change it back after of course. Failing that might be worth seeing if there is dampness in the walls creating a continuity. I take it that the MCB on the lighting circuit isnt blowing at the same time as the RCD on the other side of the board?

 

[aaelectric]

No mcb stays on when RCD trips goin there today so will let u know how I get on

 

[mickys86]

Take the earths out connect them one by one and that will tell you if there is a fault on a certain circuit

Mcb stays on which means the fault is either the RCD or between N and cpc

 

[tony mc]

My understanding is that you have disconnected the busbar from the RCD but left it energised with only the neutral load connected.

When switching the lights on which are fed from a seperate none RCD busbar and seperate neutral bar the other RCD trips.

You have IR tested between neutrals and this is clear.

IMO I would say the the RCD is faulted or you could have a bad /loose connection on the supply side of the RCD.


However you say the RCD will not 1 x trip so my money is on a faulted RCD!

 

[aaelectric]

Guys went back to the job today and found a short from n to e on a completely different circuit one I disconnect all was well. Just goes to show the RCD doesn't make clear what circuit has a problem and the way forward is RCBO s happy days

 

[keefy]

Just goes to show those neutral to earth faults make things act wierd. Any wierd RCD tripping now and I am 95% certain it's N-E fault.

 

[mickys86]

Guys went back to the job today and found a short from n to e on a completely different circuit one I disconnect all was well. Just goes to show the RCD doesn't make clear what circuit has a problem and the way forward is RCBO s happy days

RCBO route would be great if only they didn't cost around £30 each. I wonder how long it will be before split load boards will be frowned upon and every circuit on an RCBO will be all part of the regs