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Recently had an electric cooker removed, the wire was left hanging out of the connection unit having been disconnected at the cooker end (all switched off at the consumer unit). I think the bare earth was touching one of the other two wires. My question is why did the RCD trip when I turned the cooker switch on? It was still off at the consumer unit.
 
A connection between Neutral and earth would create an alternative path for the current in the house to flow and cause the RCD protecting the cooker circuit to trip. Even though it was off at the consumer unit this does not disconnect the neutral or earth only the line.
The cooker switch would disconnect both neutral and line and so would not permit a trip to occur.
 
I sincerely hope it was also disconnected at the other end in the fuse box, or distribution box/consumer unit! Sounds like it is not if the RCD can trip. That "wire" should not be hanging around either, unless you have another cooker to put in ?
 
A connection between Neutral and earth would create an alternative path for the current in the house to flow and cause the RCD protecting the cooker circuit to trip. Even though it was off at the consumer unit this does not disconnect the neutral or earth only the line.
The cooker switch would disconnect both neutral and line and so would not permit a trip to occur.

Generally this will only occur on a TNCS supply though, annoying and sometimes embarrassing explain why cutting through a 'dead' cable has activated a customers RCD. :)
 
Thanks all for your comments. So it sounds like it's normal behaviour for a RCD to trip if earth and neutral connect on a dead cable, I was worried it might indicate some kind of fault. For the record I think my wiring is TNS (earth is taken from the supply sheath).
 
A connection between Neutral and earth would create an alternative path for the current in the house to flow and cause the RCD protecting the cooker circuit to trip. Even though it was off at the consumer unit this does not disconnect the neutral or earth only the line.
The cooker switch would disconnect both neutral and line and so would not permit a trip to occur.
Generally this will only occur on a TNCS supply though, annoying and sometimes embarrassing explain why cutting through a 'dead' cable has activated a customers RCD. :)

Errr, maybe I'm going senile, but the supply characteristics are irrelevant if you make a N-E connection, it's going to trip the RCD associated with that Neutral. o_O

I'm more than happy for you to prove me otherwise though! :)
 
Thanks for asking Dave, yeah he's doing fine thanks. I let him do a fair bit of testing on Friday during a board change [the dead parts] and he had it off really well, the only real distraction is his current girlfriend. [4 months now which is a record :p]
 
Generally this will only occur on a TNCS supply though, annoying and sometimes embarrassing explain why cutting through a 'dead' cable has activated a customers RCD. :)

I'm intrigued by this. Why would this not also happen on a TNS supply? Daz
 
It sometimes will and other times doesn't Daz , not certain why but it may have something to do with the distance before the neutral and earth ultimately become one, and there's often a very small voltage on a TNCS neutral which the RCD will detect when it shorts to earth ?
 

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