RCCB tripping - help needed..

[binky]

I bought a clamp ammeter years ago, thinking I could use it for earth leakage, but it isn't sensitive enough, and the clamp is too large to be much use. So be careful what you buy.

 

[mattydubster]

Yes I have actually bought one!  Been playing around with it on a job today just to see what readings I came up with.  I can see it being very useful!

 

[kerching]

Yes I have actually bought one!  Been playing around with it on a job today just to see what readings I came up with.  I can see it being very useful!

Which one!

i think mine might be a DiLog 

 

[Doc Hudson]

Hi everybody.  First time post so please be gentle...

I have just been to a house after a friend of mine has appeared to uncover a fault with a Crabtree 3 module RCD on a split load board that keeps tripping out 

The RCD behaves quite erratically when all circuits are on, i.e. it sometimes works well on a ramp test and sometimes trips out on half rated.  So you'd think that I just change the RCD and everything would be ok.  I ordered one of Ebay and fitted it....and got the same problem.

Sorted!  

Ok, so I did a ramp test with everything disconnected and it popped out at 25mA then added the circuits one by one and got a leak of only about 3 or 4 mA, that's with all appliances etc connected.  Until.... I turned on the final circuit which is an old immersion heater circuit that supplies a lift -then I could barely get the trip to stay on and couldn't get a ramp test reading either.  Switched off the isolation switch at the lift end and everything was perfect again.  

So I switched everything off and did IR on the lift circuit with the lift isolator switched on.....L/E & N/E were perfect.  I then did a ramp test with just the lift on and it tripped at 19mA.

Did the only thing I could do - put the Lift on a separate RCBO  and then everything was completely fine!

Thanks for your help people

So to summarise:-  By not doing comprehensive testing to start with, you wasted time and money purchasing replacement RCD, only to find the fault was not cured. For the sake of others reading this thread I must make it clear that It is very easy to test if an RCD is operating correctly within its prescribed limits for compliance with BS7671. (NOTE: testing is done with loads DISCONNECTED). If the RCD is operating within its specification, then the fault is elsewhere. And if more than one circuit is supplied from an RCD it can be argued that this does not comply with BS7671 (reg 314.1). Multiple circuits via a single RCD immediately suggests checking for cumulative leakage if an RCD trips unexpectedly.

Doc H. 

 

[mattydubster]

Every day is a school day.  The main thing I have learned about this is the fact that although an IR reading can be really good, there can still be issues with the circuit.  I don't have a clue about how lift systems work but assumed that maybe a slight fault perhaps developed after it had been on a while and everything had gone through its own startup sequence.  I don't know.

The clamp meter I went for was (by accident) the same as the chap on this video had - He seemed to like it and I got it for £62 from Ebay!  Don't know how long it will last but we'll see!

 

[Murdoch]

FWIW ........... in most domestic properties, you don't really know whats being used and when ........a clamp meter will give you a clue as to the background leakage ........ then by turning off the MCB's 1 by 1 you can get closer to the leakier systems

The 18th edition refers to us sparks considering earth leakage when designing installations - which is madness as we have no idea what people will actually be using and also with shared RCD's you have to track down the circuit with the problem too. RCBO's for all circuits IS the best way to consider earth leakage and then minimise the chance of  nuisance  tripping

I've got the older version of this:

https://www.test-meter.co.uk/metrel-md-9272-trms-leakage-clamp-with-power-functions/?utm_source=google_shopping&gclid=Cj0KCQjwrJ7nBRD5ARIsAATMxssNkIsfphWqtbYLVY5ObW4Bp8V81l2yVDNozVF_rnWNOvUKQHFtIogaAmVGEALw_wcB

Worth every penny