Earth leakage nuisance tripping

[Strima]

The OP hasn't mentioned the type of tests he carried out, that's the way I read it. If the circuits have been IR'd then I'll shut up and move onto clamping the earth.

If D2E could list the specific tests carried out it would be easier to advise. Also incoming voltage and Ze etc.

 

[i=p/u]

the ciruits will be fine its the appliances / loads . come on.........

 

[Jimmy Boy]

Looking back at the first post it states he has run a second CU to a garage, presumably from the original CU so I hope he either split the tails to serve this or perhaps he managed to get a pair of 16's in the incoming side of the main switch/RCD otherwise there would be no discrimination

J

 

[Strima]

If I turn off one circuit (doesn't matter which one) this seems to be enough for the RCD not to trip, so I guess the problem is cumulative earth leakage??

Just re-read your Op, Think of how each circuits neutral and earth are terminated. This is why I'm wondering if an IR test has been done on each circuit, a global one may be within the required limits however resistance in parallel could give false readings.

 

[Guitarist]

Guys, you are probably right. I assumed (maybe wrongly) that the op had carried out all the usual tests. I realise that we should never assume anything, but I still stand by the fact that clamping for leakage would probably be the quickest thing to test. As he doesn't have a clamp meter, then it's not gonna be quick

 

[Strima]

I'm never right, I just like to add to the confusion... :lol:

 

[Jimmy Boy]

Strima your quite right parallel resistances will lower the figure but you would need a hell of a dis board to have enough parallels to reduce it to <1M

J

 

[Strima]

Edit, as I'm confusing myself now... Not hard before you say it. On a global test the measurement may be >1M however the leakage across one or several circuits may be enough to trip the RCD especially as loads increase such a refrigeration/PC's etc kick in.

 

[Jimmy Boy]

What do mean by a bad one? What I meant was that if all insulation was in good order ie not breaking down you would need a huge amount of parallel resistances via circuits to lower an otherwise good IR reading, if you had one leaking like a sieve on a bit of old rubber of course it would drag the overall down and you would start splitting them

J

 

[Strima]

As I said, I'm confusing myself. I meant to say accumulative effect over all circuits.

And you may have been posting when I edited my original post.

 

[down2earth]

Looking back at the first post it states he has run a second CU to a garage, presumably from the original CU so I hope he either split the tails to serve this or perhaps he managed to get a pair of 16's in the incoming side of the main switch/RCD otherwise there would be no discrimination

J

The garage CU is fed from a 63A MCB in the main house CU so discrimination would be an issue until I change the main RCD switch to a non RCD one and change the house MCB's to RCBO's. The fact that there is no discrimination at the moment, that presumably wouldn't be the cause of the tripping?

 

[Strima]

The annex that has been wired, although it is on a TT has the earth been exported to the new CU as well? Or is the SWA armouring/earth only terminated at the supply end?

 

[down2earth]

The annex that has been wired, although it is on a TT has the earth been exported to the new CU as well? Or is the SWA armouring/earth only terminated at the supply end?

The armouring earth has only been terminated at the supply end, I haven't exported the earth.