RCD main switch tripping

[ExArmy]

had a call out today where the RCD would not hold, at first i hadall the MCB's off and ramp tested the RCD and it was tripping at 12-13 mA consecutively.
i've briefly tested all the circuits and theres no earth fault, i've had a clamp meter on the earth and switched on all MCB's individually and then without warning it will just trip, generally as more load was put on. Ie i could put on boiler(combi), cooker (turned off) and up & down lights and it was fine, even with 1 ring on it was fine but as soon as both rings were on it would trip. then sometimes it would hold for 30-40 seconds and trip. also another point to note if i tapped the RCD main switch it would trip. now i don't think thats normal? it's a wylex btw. i have just got home and i have been giving all my square d rcd a good tapping and none of them go??

right then bear with me, all of a sudden i did a full rcd test and it was fine, rcd tripped promptly at x1 and x5, never tripped at x1/2 and ramp test showed 27 and 28 ish mA. the i flicked on all the breakers and it held, and then i got them to boil the kettle and had the clamp meter on live and it was pulling 14A no problem:crazy:
i left them my card and said if it does it again it's likely to be the RCD MS and i'll change it on monday or them.
i hate faults like this, if it had been a private job i wouldn't have taken any money off them as it could go as soon as i walk out the door and then i'd look stupid! it was for a letting agency so i'll invoice them directly on monday if it's still ok, or if it's gone again i'll change the RCD.

oh and something else that might be of relavence, the street was without power the day before, and the problem first occured after that so is it a possilbility that some works by the DNO could have damaged the RCD main switch?

 

[Guitarist]

I would be tempted to just change it mate. Chances are that there is an internal fault that will rear its head at some point in the future and you will be expected to put it right pronto.
Either that, or tell them that you can do it now, or later if they don't want to spend the money, but that later will incur an additional call-out fee.

 

[ExArmy]

well doing it today was not an option, i got there at 12.45 all 3 wholesalers close at 1pm, i tried at 12.55 to get one but the guy was nearly out the door and wouldn't wait for me to travel 15 mins!
i did call B&Q but the moron on the end of the phone didn't have a clue what i was asking for, and told me there should only be one rating in A, not a 100A 30mA!! he said the part i was probably looking for was a 40A as it was the highest they do in wylex, to which i replied thats an MCB surely? to which he said yeah thats right. me: has it got a button on it? B&Q: yes it's got a button Me: and a on off switch that flicks up and down? B&Q: you mean the button, yes it's got a button! then i hung up. later i looked in the B&Q trade point catalogue and they don't have one in wylex anyway, but but a 63A 30mA is £50!! also i noticed my favorite 10 way dual rdc board (B&G) is £41.66 from there, yet i've been paying £50 plus VAT from my local wholesaler. how can they do that??

anyway,back to the fault. i'll speak to the letting agent on monday and tell them i can change it if they want , if not just bill them callout and 2 hours and leave it.

 

[topquark]

Also seen problems with the main neutral tails being loose causing those symptoms. I think it was IQElectrical had also seen a problem where the loose neutral was actually in either the service head or meter. Worth checking the main neutral tail when you go back (they do compress after a while, as I'm sure you are aware).

 

[joe j]

one but the guy was nearly out the door and wouldn't wait for me to travel 15 mins! i did call B&Q but the moron on the end of the phone didn't have a clue what i was asking for

Think we've all been there!

 

[Moses]

had a call out today where the RCD would not hold, at first i hadall the MCB's off and ramp tested the RCD and it was tripping at 12-13 mA consecutively.
i've briefly tested all the circuits and theres no earth fault, i've had a clamp meter on the earth and switched on all MCB's individually and then without warning it will just trip, generally as more load was put on. Ie i could put on boiler(combi), cooker (turned off) and up & down lights and it was fine, even with 1 ring on it was fine but as soon as both rings were on it would trip. then sometimes it would hold for 30-40 seconds and trip. also another point to note if i tapped the RCD main switch it would trip. now i don't think thats normal? it's a wylex btw. i have just got home and i have been giving all my square d rcd a good tapping and none of them go??

right then bear with me, all of a sudden i did a full rcd test and it was fine, rcd tripped promptly at x1 and x5, never tripped at x1/2 and ramp test showed 27 and 28 ish mA. the i flicked on all the breakers and it held, and then i got them to boil the kettle and had the clamp meter on live and it was pulling 14A no problem:crazy:
i left them my card and said if it does it again it's likely to be the RCD MS and i'll change it on monday or them.
i hate faults like this, if it had been a private job i wouldn't have taken any money off them as it could go as soon as i walk out the door and then i'd look stupid! it was for a letting agency so i'll invoice them directly on monday if it's still ok, or if it's gone again i'll change the RCD.

oh and something else that might be of relavence, the street was without power the day before, and the problem first occured after that so is it a possilbility that some works by the DNO could have damaged the RCD main switch?

Check all the cables to and from the RCD as already said in post#3, All cables for tightness + the RCD busbar.

Symptoms like a loose connection.

 

[trev]

i did call B&Q but the moron on the end of the phone didn't have a clue what i was asking for

How dare you criticise their friendly helpful experts in such a manner

 

[ExArmy]

well during all my testing and fiddling about i did nip up all the neutral connections and got 1/4 turn on a few of them and they are all tight now. i've still not had a call about it and i did say to call if it tripped again so i assume it's still ok...

 

[Guitarist]

well during all my testing and fiddling about i did nip up all the neutral connections and got 1/4 turn on a few of them and they are all tight now. i've still not had a call about it and i did say to call if it tripped again so i assume it's still ok...

I hate jobs like this... The problem may have disappeared for good and you will never hear from them again, or you may get a call at 10pm one day saying "It's done it again. You did say to call if it happened"

 

[ExArmy]

called back this morning, had done it a few times over the weekend so i went to replace the RCD MS. once i replaced it i was doing a few tests and when i tried the main bedroom light (2 way) the switch arc'd a bit and tripped the MCB. upon closer inspection the T&E switch drop from the light to the first switch had low IR L-E (about 700ohms) so fixed that and it's all sorted. weird how that was causing those problems...

 

[Moses]

called back this morning, had done it a few times over the weekend so i went to replace the RCD MS. once i replaced it i was doing a few tests and when i tried the main bedroom light (2 way) the switch arc'd a bit and tripped the MCB. upon closer inspection the T&E switch drop from the light to the first switch had low IR L-E (about 700ohms) so fixed that and it's all sorted. weird how that was causing those problems...

Well done

All sorted then?

 

[ExArmy]

i hope so!