RCD tripping... something odd here....

[matt.leung]

being carrying out a PIR inspection, and i am havng issues with RCD trip times on one particular circuit. The circuit is a the downstairs lighting...

the same RCD protects other circuits as well.... but this lighting circuit will trip

1x at 400 ms

5x will not trip/error

i know that there is an earth as the Zs is 0.66ohms

 

[Andy™]

have you tested in isolation?

may be a faulty RCD

 

[matt.leung]

cos my thoughts are how could it be a faulty RCD if the RCD trips when tested on other circuits... split load board...

 

[Andy™]

various loads on circuits are known to stop an RCD operating as it should. which is why RCD's should be tested at the closest point, and in isolation where possible.

but at the same time, removing a load to get it to pass doesnt sound right...

 

[Theorysparky]

Matt

not sure why you are testing the lighting cct for rcd trip times

nearest socket to board is all you need to do

having said that it seems strange that it is happening,,, are you testing at the furthest point ? or closest ?

 

[matt.leung]

on a cu change, i alway test the the RCD works for every circuit.. just to be on the same side... it might be ott but better to be safe than end up in the dock in court...

 

[wozz]

as theory said id be testing at the nearest socket and only testing the RCD on one circuit.

 

[bengie]

i had this disagreement with a colleague, he always said you only need the RCD from one circuit and you can carry those readings over to other circuits but think you should test on every circuit regardless of what OSG etc say as the characteristics of a circuit such as ZS will affect things like RCD timings.

 

[mickey g]

if you only test on the nearest socket to the rcd then you can only confirm that that socket/circuit has suitable rcd protection.surely if a fault were to occur in an upstairs bathroom you would want the rcd to trip within the proscribed times regardles of what else is connected to other circuits being protected by the same rcd, you dont go around unplugging everything just prior to a fault occuring therefore the rcd should operate regardless if not then there must be something wrong with the rcd or these types of rcd are not fit for purpouse.does the same issue arise with rcbos?if not then they should be used,and rcds protecting mulipule circuits discontinued.Rant over thank youX(X( X(

 

[Lurch]

if you only test on the nearest socket to the rcd then you can only confirm that that socket/circuit has suitable rcd protection.surely if a fault were to occur in an upstairs bathroom you would want the rcd to trip within the proscribed times regardles of what else is connected to other circuits being protected by the same rcd, you dont go around unplugging everything just prior to a fault occuring therefore the rcd should operate regardless if not then there must be something wrong with the rcd or these types of rcd are not fit for purpouse.does the same issue arise with rcbos?if not then they should be used,and rcds protecting mulipule circuits discontinued.Rant over thank youX(X( X(

Whilst that is quite true you only need to test the RCD in one location. The other tests on each circuit should be within limits which allow the RCD to operate in the required time as that should be how it was designed and the tester should be aware of this. The RCD tests are only to test the RCD, nothing else.

 

[choccy]

this is a common occurence when rcd testing a lighting circuit because 6amp circuit breakers are very sensitive.

 

[Lurch]

this is a common occurence when rcd testing a lighting circuit because 6amp circuit breakers are very sensitive.

Are you getting mixed up with testing Zs on upstairs lighting circuits?

 

[matt.leung]

nope down stairs lighting circuit... for sure...

 

[paul b b]

matt, maybe a long shot but if poss try wiring up a socket on to the lighting and testing with the plug attachement

 

[steptoe]

test the RCD at the consumer unit.

as has been said, your R1R2 test and your Zs is proof that the RCD will function inside the parameters allowed in case of a fault.

test the RCD, NOT the circuit.

 

[paul b b]

test the RCD at the consumer unit.as has been said, your R1R2 test and your Zs is proof that the RCD will function inside the parameters allowed in case of a fault.

test the RCD, NOT the circuit.

i suppose this is a debate on if the regs want an rcd trip time or a circuit trip time

 

[steptoe]

both are allowed for, that is why you have a max Zs, and use the 4/5 ROT, to allow for overheating in fault. if your Zs is within limit then the protective device will/should disconnect the supply, according to the BRC that is, and after all, you will be using that as your defence in court, NOT your opinion.

 

[choccy]

yes you are correct lurch my mistake they trip frequently when doing earth loop, your are very correct my appoligies, got mixed uo as watching football.GuinnessGuinness

 

[ADS]

Amazing how many 'scheme registered' sparkies have no idea what they're doing when testing an RCD.

You are not confirming that individual circuits have RCD protection!

Zs has nothing to do with RCD operating times!

You are confirming that the RCD will operate within the prescribed time, at the rated test currents - that's it

unless you are doing the ramp test, which will tell you the current that the RCD is tripping at........

.........so test (once) at anywhere you like - nearest socket is most convenient - and record the results.

Matt - I was gonna suggest a neutral/earth fault or a borrowed neutral on your downstairs lighting might be messing up the trip times - but then - these would have been shown up on the dead tests

Cheers

 

[choccy]

scheme registered or not Zs does not indeed come into play when functional testing the rcd but as lurch says when testing Zs the rcds very often trip.headbangheadbang