Earth used as a neutral?!?!

[alexg]

I've got this job where the owner says he definately knows that the earth on a circuit is joined to a neutral!!! He saw it in a JB that had a loose lid he screwed on before a new ceiing was put up. I need to put an RCBO on teh same lighting circuit on that floor. The mcb trips when teh boartd is powered up, but works once it is reset.

There is no ceiling access from abover the jb... anyone got any ideas as to why this may have been done in the first place and what a relatively simple solution may be... apart from connecting the earth at the cu to the neutral bar!! All a bit weird if you ask me.

Thanks guys!!

 

[mrloy99]

I've got this job where the owner says he definately knows that the earth on a circuit is joined to a neutral!!! He saw it in a JB that had a loose lid he screwed on before a new ceiing was put up. I need to put an RCBO on teh same lighting circuit on that floor. The mcb trips when teh boartd is powered up, but works once it is reset.

There is no ceiling access from abover the jb... anyone got any ideas as to why this may have been done in the first place and what a relatively simple solution may be... apart from connecting the earth at the cu to the neutral bar!! All a bit weird if you ask me.

Thanks guys!!

I don't think you should connect cu earth to neutral bar.Inside the supplyers end box,there probably will already be a common connection.This is the only place this should be done.You could maybe cut a neat handhole close to where the j.b. is. to check out the connections,this could then be replaced and patched in as required.
Perhaps ,only a wide guess here,some oddball has connected an extracter fan unit to the circuit and has only installed a twin and earth cable to feed it,and has used the earth core as a neutral,as he has had to use the other two cores as perm.live and switched live,and had no tape to sleeve the neutral,odd I know,but I have seen it done before! Though
the fact that your(mcb you said)rcbo is tripping would indeed suggest a short on circuit,though not quite sure why it holds when you reset.It should be quite easy to test at the consumer unit,with a continuity tester,if you do indeed have a short between your circuit neutral and circuit earth. Best of luck.

 

[WarrenG]

J.B. should be accessable anyway (Regs) and if the wiring is as it is, it should be corrected.

Sounds like you going to have to do some testing and check to see if there is a direct short on that circuit.