RCD tripping under high load on 2 circuits

[Lucien Nunes]

Classic symptoms of a typical N-E fault, usually on a circuit on the RCD that is tripping. But the loads that trigger it need not be on the same circuit, or even the same RCD, as any load on the CU will cause voltage drop on the supply side.

So, one circuit on the left RCD almost certainly has an N-E fault. Testing required to find which. Bear in mind it can also be something plugged into a socket, so try unplugging everything from the left RCD's sockets. However if very light loads such as individual lights trip it, the fault is more likely to be on that circuit. BTW the TV is not a heavy load, 100 watts or so unless its over 40 years old.

 

[Sintra]

@Simonw586 Looking at the first picture it looks like there is no neutral on the outgoing side of the right hand RCD. The neutral going to the right hand neutral bar appears to be coming from the main switch and not the outgoing side of the right hand RCD. Can you check that out and confirm?

 

[Wilko]

Looking at the first picture it looks like there is no neutral on the outgoing side of the right hand RCD. The neutral going to the right hand neutral bar appears to be coming from the main switch and not the outgoing side of the right hand RCD. Can you check that out and confirm?

Eagle eyes Sinatra .

 

[Wilko]

Ha, ha, I’ve just noticed my spell checker converted you into a famous singer, sorry about that !

 

[telectrix]

Ha, ha, I’ve just noticed my spell checker converted you into a famous singer, sorry about that !

it did it My Way.

 

[telectrix]

Ha, ha, I’ve just noticed my spell checker converted you into a famous singer, sorry about that !

that's nothing .Once I had to text an Eastern lady customer, named Alka. when the text had gone, I noticed that the predictive text had called her AlkaSeltzer. She was not amused.

 

[Lucien Nunes]

it looks like there is no neutral on the outgoing side of the right hand RCD

It does look exactly like that, but I can't see how it can be. Circuits on the R/H RCD work, so that neutral bar must be correctly connected as the line appears to be. As there appear to be at least two neutral jumpers in the main switch outgoing terminal, not having one in the RCD would mean four cables disappear down behind the DIN rail but only three emerge underneath. It seems unlikely that someone would have left one unconnected, or put three in the main switch which I think we'd be able to see, so all the evidence points to this being a trick of the camera angle and in fact the neutral output link from the R/H RCD is sharply bent over towards the back of the CU just hidden by the RCD body.

 

[Simonw586]

Hi all, thank you for your replies, the problem has now been resolved. It was a cable that had been crushed in the loft supplying the first floor lighting circuit. The neutral had been crushed exposing the wire onto the earth wire. Strange how this was causing the sockets to trip the rcd also but the main thing is it’s fixed!

 

[Wilko]

And Sinatra has been rediscovered .

 

[Lucien Nunes]

Strange how this was causing the sockets to trip the rcd also

Thanks for reporting back, glad it's fixed. That behaviour might seem odd but electrically it's exactly what one would expect. The N-E fault on the lighting circuit will cause an imbalance in the RCD whenever there is any potential difference between N & E at the CU to drive current through it. That includes voltage drop due to loads on both different circuits on the same RCD, and loads on the other RCD, even loads next door if the supply is TN-S. The amount of load needed to cause a trip depends on how close to the supply the meeting point is between the faulty circuit and the load. Hence, small lighting loads on the faulty circuit itself would trip it, but on the other RCD only heavier loads such as the cooker would do so.