0 Megohms N-E and no RCD Trip

[AndyTheSpark]

Hi All

I was re-testing a brand new install for QC purposes todayand the N-E on the IR was 0 Megohms, am I right in expected the RCD to trip. Itwas a TN-C-S system so wondered if the shared neutral and earth may have aneffect?
The IR for L-N and L-E belled out perfectly, I haddisconnected both the neutral and earth from the board to avoid anyinterference. There was nothing plugged in or spurred, but I wouldn’t expectthat to matter anyway on N-E. The only thing I didn’t do was put a load on thecircuit – would this make any difference?
Can anyone shed any light?!?! Thanks, Andy.

 

[Marvo]

The RCD will only trip if there's a load on the circuit. Even with an IR of 0 Megohms N-E there will be no actual leakage current if there's no load on the circuit.

 

[rapparee]

The rcd wasn't live?

 

[guest119]

You say 0 megs but did you try to read ohms? If so what was it, minus the leads?
Were you testing from the db or in the field?
Sounds like you took the wrong neutrals out the db though.

 

[Octopus]

Hi All

I was re-testing a brand new install for QC purposes todayand the N-E on the IR was 0 Megohms, am I right in expected the RCD to trip. Itwas a TN-C-S system so wondered if the shared neutral and earth may have aneffect?
The IR for L-N and L-E belled out perfectly, I haddisconnected both the neutral and earth from the board to avoid anyinterference. There was nothing plugged in or spurred, but I wouldn’t expectthat to matter anyway on N-E. The only thing I didn’t do was put a load on thecircuit – would this make any difference?
Can anyone shed any light?!?! Thanks, Andy.

Hum, probably only you when you report back on your follow up investigation!

I'd start by pluuging something into the socket concerned and see what happens next!

 

[AndyTheSpark]

The RCD will only trip if there's a load on the circuit. Even with an IR of 0 Megohms N-E there will be no actual leakage current if there's no load on the circuit.

Thanks Marvo, that makes sense!

 

[Deleted member 26818]

Was the main isolator open or closed?
Did you disconnect the conductors from the board?

 

[Knobhead]

The RCD will only trip if there's a load on the circuit. Even with an IR of 0 Megohms N-E there will be no actual leakage current if there's no load on the circuit.

Thanks Marvo, that makes sense!

No it doesn't.

 

[LeeH]

It will still trip with no load.

 

[Deleted member 9648]

Seems random sometimes,I've known the RCD on a N-E to trip with no load on plenty of occasions.

 

[Deleted member 26818]

It depends whether it's an RCD covering a number of circuits or just a single circuit.

 

[SPARTYKUS]

Hi All

I was re-testing a brand new install for QC purposes todayand the N-E on the IR was 0 Megohms, am I right in expected the RCD to trip. Itwas a TN-C-S system so wondered if the shared neutral and earth may have aneffect?
The IR for L-N and L-E belled out perfectly, I haddisconnected both the neutral and earth from the board to avoid anyinterference. There was nothing plugged in or spurred, but I wouldn’t expectthat to matter anyway on N-E. The only thing I didn’t do was put a load on thecircuit – would this make any difference?
Can anyone shed any light?!?! Thanks, Andy.

hi Andy

"0 MegOhms" could mean 872,176 Ohms.

If you use Ohms Law you'll get a rough idea about the limit at which an RCD (might) trip.

it will be alot less than the above!

 

[Deleted member 9648]

hi Andy

"0 MegOhms" could mean 872,176 Ohms.

If you use Ohms Law you'll get a rough idea about the limit at which an RCD (might) trip.

it will be alot less than the above!

I think you'll find 872,176 ohms would read 0.8-0.9 megs on the average IR tester...not 0 megs.

 

[SPARTYKUS]

Have I got mixamatosis..... Ah apologies if I am a digit out. Not near it (on holiday) so a bit off the mark. Maybe its down to 0.1 M Ohms. Same thing though under that it'll just read "0" on alot of testers.

which isn't necessary true. So my point stands.

Sort of.

back to the San Migger

 

[telectrix]

old peculier for me.

 

[Knobhead]

It may help if the OP used the correct range on his meter.