Dead short between line and neutral- RFC

[telectrix]

has someone wired an immersion heater on the rfc? that will read about 20ohms.

 

[pencilpusher]

Yes, I have 0.00 Meg on one RFC and 0.30 Meg on the other.

 

[Octopus]

Hum, 0.00 looks like a bulb as I presume the old board wasn't blowing fuses.

How old is the house?

 

[ringer]

I had a similar 'fault' recently giving an IR of 0.3M which had me scratching my head until I realised that an extension lead that could not be removed had surge protection. I rewired a different extension block and the fault cleared. If you have not actually been able to physically remove any plugs from sockets, what is still plugged in?

Sent from my HTC Sensation using Tapatalk

 

[pencilpusher]

Thanks for all the advice. Before I answer individual questions I would like to update on results I got just now. I have tested between L&N and Earth at 500V. One RFC gives 4.20Mohms and the other 2.20 Mohms. Surely there is more to this than a load on the circuits? Not sure, just asking. Thanks. PP

EDIT: The installation is 10 years old and it has not been modified at all.

 

[DaveyD]

Is the insulation damp? Any outside lights, sockets etc. Are your batterys ok in your tester?

 

[pencilpusher]

Is the insulation damp? Any outside lights, sockets etc. Are your batterys ok in your tester?

No outside lights or sockets on RFC. Batteries are brand new - yesterday!, Could be damp somewhere I suppose. It's just that getting poor results on L&N and low ones on L&N to earth makes me think there may be more to it. ??

 

[DaveyD]

are the results creeping up when you hold test?

 

[DaveyD]

I unplugged everything and turned off what i could not unplug. There are some sockets that I cannot get to to pull the plug but can turn the sockets off. Would this still affect results?

OK QI moment here, where Im totally wrong and everyone jumps on me but...

1. Were all contuinity steps ok?
2. If plugs are switched off but some left pluged in (as you state) and these sockets are single pole switching then would not a lines to earth test be sending the test into the plug tops and appliance wire via N and E?

 

[the pict]

Yep DaveyD's Right start at the start, 2 RFC'c ID the ends of each ring on each RFC and continuity checks by whatever method you prefer, but for problem rings I like to establish the ring by doing an all conductors connected together at the board on one leg only, take a reading on the other leg on L&N then N&E then check all round looking for the readings decreasing, but first your gonna have to get all the plugs out,
You may well have the RFC's interconnected and if one ring has something plugged in or an other issue it will show up on both
Pict

 

[Octopus]

Something still plugged in? display cabinet lights? light in cupboard understairs??

 

[pencilpusher]

OK. Been testing. There is some creep on one of the RFC's. One RFC I got to 5.23 Mohms slowly. The other remains at about 2.40 Mohms (All L&N to earth at 500V). I have already done full continuity tests and got good results in line with what i would expect. I was under the impression that if I did L&N together to Earth then it should not matter if something is plugged in? There is an issue here but I do have an acceptable L&N together with Earth at 500V This is within the Regs though isn't it even though I need to do some investigation. If there is an interconnection anywhere I won't be impressed. This was installed by a "reputable" contractor when it was new and I KNOW nothing has been altered. Cheers PP

 

[DaveyD]

The crossover continuity will show if interconnected or not.

Regarding the Lives to earth, as you know it's so you dont damage any sensitive equipment or neons etc that can't be removed for the test BUT (I may be wrong), I always unplug too as on a single pole switch - even if switched off you are still going to get N and E and therefore "testing" the plug top and wire of the appliance. Happy to be contradicted.

 

[the pict]

L&N to E and you still get a poor reading, so either L or N is getting to E, or E is trying to be N or vice versa, have you carried out similar tests on the lighting circuits ?? earthing issue, thinking out loud here
Pict

 

[pencilpusher]

L&N to E and you still get a poor reading, so either L or N is getting to E, or E is trying to be N or vice versa, have you carried out similar tests on the lighting circuits ?? earthing issue, thinking out loud here
Pict

All 7 other circuits give very good results - most, not all are >999 Mohms via L&N, N&E and L&E. The lowest is 250 Mohms on one circuit.