Cooker disconnected, RCD trips

[joolsmy]

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.

 

[Richard Burns]

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.

 

[The Ghost]

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 ?

 

[Pete999]

What he said ^^^^^^^^^^^^^^^^^^^^^^^^

 

[Dave OCD]

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.

 

[joolsmy]

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).

 

[Deleted member 26818]

even though your installation may be TN-S, elsewhere on the network will be TN-C-S.

 

[The Ghost]

Yeh but you still need to disconnect the circuit properly its dangerous as it is.

 

[Taylortwocities]

What he said ^^^^^^^^^^^^^^^^^^^^^^^^

 

[Silly Sausage]

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.

I'm more than happy for you to prove me otherwise though!

 

[Taylortwocities]

It's not a dead cert that the RCD will trip. It depends a bit on what other currents are flowing in the installation.

 

[2nd best]

get the cowboy back to disconnect the cooker like you asked but this time he can do a proper job yeeeehaaa

 

[7029 dave]

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.

I'm more than happy for you to prove me otherwise though!

Course it will.

 

[Dave OCD]

Not usually the case with a TT system in my experience. [With the live isolated of course]

 

[7029 dave]

Not usually the case with a TT system in my experience. [With the live isolated of course]

Yeah with a site RA lol, hows the lad doing Dave,?

 

[Dave OCD]

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 ]

 

[7029 dave]

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 ]

Keep him bloody focused.

 

[The Ghost]

:gru:Disconnect the Cooker properly !

 

[DPG]

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

 

[Dave OCD]

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 ?