One for the theorist amongst you...........................

[SirKit Breaker]

Right then,

Got a call from a friend, who has a friend who has just bought a house, and he is having electrical problems, can i have a look. Nowt else better to do, so why not, and i could use a few beers.

The house has been fully renovated back to brick etc etc, including a full rewire, complete with EIC, inspection and test result sched's, by a local Elecsa reg contractor, and building regs compliance notice is present from Elecsa.

First imprssions, the paperwork looks good, and a few random tests bear out that the testing appears to be sound and accurate. All installed accessible equipment is good quality, all the minor detail is present like sleeving in switches etc, and the CU is Schneider split load 5+5, and it has been installed to a high standard of workmanship.

All in all it looks a good install.

A couple of minor faults, one being the new (old second hand) electric fire trips the RCD, pat tested and binned it.

Upstairs lights tripping RCD, intermittent. decorator has had pendant covers off, and has been a bit rough refitting them, tidied up inside and refit, no more problems.

THEN..................Can you have a look at this socket, when i plug the microwave in, its OK but when i set it to cook it trips. And sure enough it trips the RCD for the kitchen ring, its OK when the clock is on, but when in use it trips the RCD. Duff microwave i say, but it works OK in all the other sockets he says, and it does! I tried a few other appliances in said socket, and they all work fine as well. Just out of interest i fully tested the circuit, and my test results were almost identical the ones on the cert, and all well within spec, and as you would expect for a new circuit. I replaced the socket, and the same thing happens, so, ANY IDEAS, cos i aint got a clue, but i refuse to be beaten.

I PAT tested the microwave, its not perfect, but it is well in at 0.06ohm, and 30 odd meg.

The install is TNCS. 0.18ohm Ze, 1.3kA PFC. The PME connection is new, as recommended by the contractor who reported a high Ze on the previous TNS of 200+ ohms.

Answers on a postcard please or PM me or post a reply.

Cheers......................Howard

 

[shanky887614]

are these deta by any chance? couple duff sockets in my house.

i dont like them. half a socket stops working!!!!

i wouldn't be surprised if a replacement was bad as well, im saying nothing more on there qualify control

 

[SirKit Breaker]

are these deta by any chance? couple duff sockets in my house.

i dont like them. half a socket stops working!!!!

i wouldn't be surprised if a replacement was bad as well, im saying nothing more on there qualify control

The one i took off looked a bit like the screwfix contractor ones, and to be fair i have used these previously without problems, i have replaced it with a crabtree.

 

[ImpededLoop]

Reversed cpc and neutral at that socket? Or possibly dodgy socket outlet.

 

[SirKit Breaker]

Reversed cpc and neutral at that socket? Or possibly dodgy socket outlet.

The circuit tests out perfect, see first post! the socket has been replaced by me, and the problem persists!

 

[Octopus]

Do you know the reason?

 

[ImpededLoop]

The circuit tests out perfect, see first post! the socket has been replaced by me, and the problem persists!

Sorry, should of guessed it wouldn't be the obvious! .

I'll think it through and reply if I can think of another likely cause.

 

[ruston]

What condition is the inside of the plug top and cable entry , and possible earth leakage on the microwave. I know you have tried it in other sockets, but it sounds as though it could just be a bad connection on N or E.

 

[R G]

Just a thought , have you tried unplugging every thing else on this circuit or every appliance thats controlled by that RCD , just thinking this could be cumulative with other appliances connected , the other thing I would try is an Earth leak clamp meter with each appliance in use ...
It could be the socket the microwave is plugged in is at the lowest Zs point on the circuit and is just taking it over the limit at that point , (microwave faulty)

 

[Simonslimline]

Could an IR test at 1000v possibly highlight an issue that 500v would not?

 

[Adam W]

(null)

 

[Besoeker]

The circuit tests out perfect, see first post! the socket has been replaced by me, and the problem persists!

Wouldn't you then suspect the appliance?

 

[Octopus]

Have you clamped the tails? I would venture to suggest that the "backgroun" leakage is high and the microwave simply tips the RCD "over".

 

[R G]

I had a similar problem once on an old microwave and even though testing the MW proved o/k , when in use it did trip the RCD , If this mate has just moved in with this MW , I would have thought any issue with wiring faults would have been sorted by previous owner , as they would have had a MW and the installation is new .

 

[ruston]

Another thing is the other sockets that have been tried been vacated of an appliance to accommodate the microwave, hence lowering the leakage on the circuit.