RCD issue

morpheus75 · Feb 17, 2011

hello all
i have an installation domestic and all tests were fine and the rcd never tripped at all. now th efamily have moved back in and we get random tripping mainly at night.
the only 2 appliances that were plugged in before the move were fridge and kettle. after moving in they have their other kitchen appliances, tv, ovens etc etc
working fine then random trips, more often at night?
going to go back on weekend and re-do standard tests again, but is there anything else i can look for/test for.
thanks in advance

BlueToBits · Feb 17, 2011

A few things you could check:
Insulation Resistance E to P&N connected together
Appliances with thermostats
Temperature related faults? A cable trapped behind a CH pipe that gets crushed as the pipe expands?
PIR Security lighting.
Equipment with switched mode power supplies. (plasma TVs, PCs etc) or other spike producing equipment.
It may be leakage from more than one appliance that when combined trip the RCD
RCD ramp test?
Water heater element
Remember that a neutral fault may not trip the RCD if there is no load on that circuit.
If all else fails try removing the RCD and replace MCBs that require protection with RCBOs. At least this may narrow down the problem.

Engineer54 · Feb 17, 2011

Get yourself a decent mA leakage clamp meter, you can then check at various locations around the suspect circuits, and find out which appliance is releasing abnormal leakage currents... That's where i would start. A reasonably priced leakage tester from Dilog is around 100 quid, and worth every penny. The amount of RCD devices that being installed these days, means you and every other electrician Needs one of these clamp meters, if your going to do any fault finding on them with any success...

Here's a link to the cheapest place i've found this model...

Dilog DL6507 10uA to 60A AC Leakage Clamp meter. Buy online or call

The forum Sponsor unfortunately doesn't carry this model. All there leakage testers are, for want of better words ''Silly Money'' ..lol!!!

trebor · Feb 17, 2011

when you say at night do you mean evening or overnight ? could it be something for instance thatis time controlled or even an iffy pir controlled light operating at night, if you have a tester with ramp test check it out, as enginneer 54 says earth leakage may be a problem even with equipment that use the cpc to filter leakages in normal operation

Engineer54 · Feb 17, 2011

BluetoBits,

Ramp tests on a RCD tester are of little use when fault finding. The ramp is conducted in multiples of mA. For 30mA it's normally 5mA from a base of 15mA (3 steps normally, more if the RCD is faulty). So as you see quite useless for fault finding. I think that most electricians think it ramps up in 1mA steps, but they Don't!!!

morpheus75 · Feb 17, 2011

Hi
Thanks for your replies i will be getting hold of the clamp ammeter, one of the tests i was going todo was a ramp test. I will check and see whats actually connected on the circuits, and take it from there. I will post my findings after checking, and like the rest of your thoughts re earth leakage i will beclooking for that.
If it is apart from changing to rcbo's is there any other 'cure'?

Engineer54 · Feb 17, 2011

Nope, .... it's a case of finding the cause of the fault and fixing it i'm afraid!!

BlueToBits · Feb 17, 2011

Engineer54 said:
BluetoBits,

Ramp tests on a RCD tester are of little use when fault finding. The ramp is conducted in multiples of mA. For 30mA it's normally 5mA from a base of 15mA (3 steps normally, more if the RCD is faulty). So as you see quite useless for fault finding. I think that most electricians think it ramps up in 1mA steps, but they Don't!!!

OK . My meter does a ramp test in 3mA steps from a base of 0, but I agree that the information could be of limited use, but I certainly would not call it useless. It can help to identify multiple leaking appliances. Yes, a leakage clamp meter would do a better job, but only if there was one to hand at the time. Sometimes any bit of information is welcome when you are pulling your hair out looking for this type of fault. For example It is very useful to know that the RCD trips at 6 mA with the dish washer on and 21mA with it off.