Tracking down earth leakage

[Adam_151]

yesterday we had an electrician in to wire the new shower, as part of that the RCD was replaced (only rated at 60A before), tested out ok and everything, when the job was done, the new circuit fully tested and everything, the mcbs for the rest of the board were switched back on, the kitchen ring which was the last one to be flicked on took out the RCD, unplugging the microwave solved it, thought maybe the old rcd was kaput and the microwave was faulty.

Anyway, kept getting nuisense trips, and when I investigated the microwave found out that it wasn't faulty as such but the filter board was leaking 2.2ma to earth (multimeter* in series with the functional earth), and microwave plugged in, the last circuit to be switched on tripped it, obviously we have combined leakage nearly tripping it, and the microwave pushing it over the edge. Temporary measure has to been to use the 'backup' microwave, but I want to find out where the rest of the leakage is comming from (because with it that close to the mark we still get nuisence trips without the big microwave), I was planning on getting hold of a clamp meter and putting it round both tails and switching on each circuit indiviudally, then dropping down to testing appliances by plugging them in one at a time. I'm hopeing though to find it to be something daft like moist dust in an outdoor junction box or something.

Just wondered if anyone else had any ideas to throw into the mix


*A new one, accepted that my old one had died

 

[JohnD]

I've found it's the "watery" appliances that have leakage:

Immersion heater; washing machine, kettle, steam iron

I've heard that fridges can leak, don't know why as they have brushless motors.

I wonder if you can hire a PAT tester? Child's play to use.

 

[RF Lighting]

What about testing the earth for each circuit to find out if there is one particular circuit that is causing alot of leakage, with the others just contributing to it. You could eithe do this like you did before but only turn one circuit on (or off) at a time, or by testing the current flow between the CPC of each circuit and earth.

Disclaimer: Only do this if you really know what you are doing, as it will require working in a consumer unit with the power on. (you seem clued up but others reading this might not be)

 

[Adam_151]

Further investigations, clamp meters appear from there specs to only read from 100ma upwards, so no good for this.

Made up a sepcial extension lead with my multimeter in the earth (yeah I know a far from elegant/safe solution.... ) found both the washing machine and dishwasher are dropping 2.5ma to earth each. So thats 7.2ma with the microwave connected, surge suppresion extension leads seem to be somewhere around 0.4 and we have four, so thats another 1.6ma, so I've accounted for 8.8ma. I've just got to try and find the rest now... then there is the issue of what will I do about it when I know where it all is... ... RCDs seem to be somewhat of a dark art...

 

[plugwash]

is this a split load board?

if so you could consider moving the kitchen to a RCBO on the non-rcd side.

 

[Adam_151]

Yes, Hager 6+6 split

There is an old unused cooker circuit (just terminated in jb in attic) on non-rcd side that could I suppose be removed, but then, are RCBOs readily available for hager boards?, then got the trouble of trying to work in a board thats quite messy, and it'll probably involve crimping and extending, then I can't test it, then theres the big P....

Its a bit of a nightmare really

 

[JohnD]

Is the Immersion heater on the RCD, or is it just sockets?

 

[Adam_151]

Is the Immersion heater on the RCD, or is it just sockets?

No immerson heater here (well there is, but not wired in... just filling the hole in the tank) CH is spured off the kitchen ring though, not sure how much that is dropping

 

[JohnD]

try the CH pump and boiler, they're wet...



p.s. If you were lucky enough to have a Mem CU, you could turn any MCB into an RCBO with a clip-on pod; 30mA or 100mA to choice... sorry

 

[Adam_151]

Just tried the CH, maybe a fifth of a muliamp, but thats there even with the FCU off, so I think thats more to do with circulating currents in the earth due to it being TNCS.

Next, the shed FCU, but thats in the loft, so I'm going to wait until the temp drops a bit before going up there...

 

[plugwash]

Just tried the CH, maybe a fifth of a muliamp, but thats there even with the FCU off, so I think thats more to do with circulating currents in the earth due to it being TNCS.

hmm the CH may be leaking down other earth paths than the circuit CPC.

 

[Adam_151]

hmm the CH may be leaking down other earth paths than the circuit CPC.

Can't think of an easy way to measure that though

 

[RF Lighting]

Just found this on Fleabay. It might be of use to you. Click Here

 

[plugwash]

hmm the CH may be leaking down other earth paths than the circuit CPC.

Can't think of an easy way to measure that though

well you can get residual current clamp meters but they don't come cheap.

one possibility is to borrow a 240-240 isolation transformer with floating output and connect the neutral side of the floating output to earth via your multimeter. That way any leakage has to go through the meter.

 

[Adam_151]

Thanks RF, I'll keep my eye on that... must have been listed recently... wasn't there when I checked an hour or two ago for them...

Would probably sneak it in when the bathroom wireing is done, either get the spark to do it, or if I have a tester myself by then and end up doing it under building notice, then it'll be another cert in the pile to pass to BC