Earth tripping rccb even when circuit breaker off

[Nick13579]

I’ve just finished replacing a light fitting, as usual I turned off the associated breaker, checked for no voltage with a detector pen, then went ahead with the replacement. However when I touch the earth, the rccb tripped causing the rest of the house’s electric to go off.

This can consistently be replicated, which I’m fairly certain isn’t normal, does this mean I have an earth fault that needs to be corrected by an electrician? Any ideas?

 

[bernardgreen]

does this mean I have an earth fault that needs to be corrected by an electrician?

Yes, but if the original light worked and tripping only occurs since you changed it then you may be able to undo the error.

How did you "touch the Earth" , finger or screw driver.

If the Neutral touches the Earth then even if the MCB for the circuit is switched OFF there can be a trip

 

[Nick13579]

Thanks Bernard, it was with a screwdriver, so there’s a chance that it could have been earth touching neutral, the diagrams really informative!

 

[Harry Bloomfield]

Thanks Bernard, it was with a screwdriver, so there’s a chance that it could have been earth touching neutral, the diagrams really informative!

Yep! Isolating at an MCB only isolates the live, neutral remains connected and will likely have a different potential to the earth - so when shorted, it trips..

 

[sparkwright]

You need to completely isolate the power so 'someone' can check the light wiring, as it seems it has been wired very wrongly.

At least, that's how it seems.

 

[ericmark]

You need to completely isolate the power so 'someone' can check the light wiring, as it seems it has been wired very wrongly.

At least, that's how it seems.

Not very practical. To isolate means turn off both lives, both line and neutral, and in many houses that means half or all the power, my house would need to be all power. With a TN supply it is permitted to just switch off the line.

I would guess it is a neutral - earth fault which is unlikely to cause a danger.

 

[sparkwright]

.

 

[sparkwright]

I’ve just finished replacing a light fitting, as usual I turned off the associated breaker, checked for no voltage with a detector pen, then went ahead with the replacement. However when I touch the earth, the rccb tripped causing the rest of the house’s electric to go off.

This can consistently be replicated, which I’m fairly certain isn’t normal, does this mean I have an earth fault that needs to be corrected by an electrician? Any ideas?

When you touch the earth.

Do you mean when you touch JUST the earth wire when installing light?

Do you mean the earth wire may have touched the neutral wire when installing the light?

I take it you don't mean you have simply touched some (earthed) metalwork of the light once it was installed (in which case you have a problem).

 

[333rocky333]

I’ve just finished replacing a light fitting,

However when I touch the earth, the rccb tripped causing the rest of the house’s electric to go off.

This can consistently be replicated,

Are you saying that it trips everytime you touch the fittings metal casing?

 

[Nick13579]

It only trips if the actual wire is touched, so once the fitting is in situ everything appears fine.

I need to check whether the issue was when earth and neutral connected or just when the bare earth wire end was touched. It sounds like if it’s just earth then I could have a problem?

 

[markyd1]

Nothing wrong...you touched neutral to earth when connecting new fitting which caused it to trip

 

[333rocky333]

I need to check whether the issue was when earth and neutral connected or just when the bare earth wire end was touched. It sounds like if it’s just earth then I could have a problem?

If you tripped an RCD just by touching the earth wire, then you would have known about it, it may not kill you but i am sure you would certainly feel 30ma passing through you