RCD intermittent fault

[swpenfold]

Hi,

Just wondering if anyone has come across this before,

we got called to a intermittent fault at a new build the owners have been moved in around 8 months, the power would
trip mainly when all the lights were switch on and in the evening when switches were turned on, but sometimes
randomly, I tested the rcd first and would test fine when lights were disconnected but not always when connected,
also when you turn off the main switch both RCDs would trip most of the time and when boiler is turned off.

Thanks

 

[Marvo]

I tested the rcd first and would test fine when lights were disconnected but not always when connected,

What tests did you do?

 

[Sintra]

Test the RCD with no loads connected. If these tests are good then the fault is on the circuits. It could be accumulative leakage or an intermittent fault which could be verified by additional testing.

 

[swpenfold]

Would come up with trp on x1/2 but would test x1/2,x1 and would trp at x5 with some of the lights disconnected, I have a megger MFT1553, also have installed new RCDs

Cheers

 

[Marvo]

As Sintra suggests, ramp test the RCD with no load connected. If it passes then start looking for the leakage faults on the circuits themselves.

 

[Anthony S]

Would come up with trp on x1/2 but would test x1/2,x1 and would trp at x5 with some of the lights disconnected, I have a megger MFT1553, also have installed new RCDs

Cheers

Posted to soon

 

[swpenfold]

Thanks for the replys, RCDs are fine on ramp test and without load, on the circuits what could be the main causes there are a lot of LED Downlights and the problem has just started?

cheers

 

[Sintra]

Read post #3 again.

 

[Marvo]

If the LED downlights have their own driver units there could be standing leakage from the internal surge arrestors. Use an earth leakage clamp around both the L+N simultaneously and switch the lights on to establish the leakage. If it's just an accumulation of many devices adding up to the 30mA threshold then you may need to reconfigure and put the circuits on RCBO's.

 

[swpenfold]

I read that, was just asking what are the main causes you have came across fridge/cookers etc that's all

 

[Octopus]

Have you got an earth leakage clamp meter?

I'd be getting mine out to determine the background leakage first!

 

[swpenfold]

If the LED downlights have their own driver units there could be standing leakage from the internal surge arrestors. Use an earth leakage clamp around both the L+N simultaneously and switch the lights on to establish the leakage. If it's just an accumulation of many devices adding up to the 30mA threshold then you may need to reconfigure and put the circuits on RCBO's.

thanks Marvo

 

[Deleted member 9648]

An RCD tripping and IR testing of circuits hasnt even been mentioned. Thats the first thing I'd do.

 

[Engineer54]

I can't see how an electrician can get by without a leakage clamp these day's to locate earth faults and RCD tripping issues , especially on dual RCD CU's. But then you need to know how to use them and interpret the values being shown!!