RCD tripped and I'm not sure why...

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I am replacing a Hortsmann h37xl and switched off the heating RCD, tested the live wire to make sure it was off and all ok. When removing the Hortsmann one of the earth wires touched the neutral wire connected to the Hortsmann and tripped the whole RCD unit. I am a novice and wondering if someone could explain why this happened? Let me know if you need more information. Thanks

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I assume you turned off the MCB to the circuit you were working on ,not RCD.
When neutral and earth conductors touched ,that would trip RCD.
MCB only isolates the line ( live) ,the neutral is still connected.
RCD detects line and neutral imbalance/ earth leakage.
 
Thanks for your reply. I turned off the heating switch as in the photo below of the consumer unit. Is it safe to be working on that circuit if I do so?
I could always flip the main switch if that is safer?

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:?: Who's a clever labeler?

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Yes it would be safer to switch off the main switch - the red one.
 
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To the left of the RCD's,are the MCB 's for each Individual circuit. An MCB is a single pole ,so it breaks only the live.
The red is main switch and isolates ALL circuits ,both poles ,live and neutral. And is much safer to use that. Its also marked up wrong.

Edit , EFL beat me to it !!
 
Ok I use the main red switch. Thanks for pointing out the incorrect labels; it's a Taylor Wimpey new build, go figure.

Out of curiosity what risks are involved with just switching off the MCB for heating and testing for absence of voltage of the live wire and then working on that circuit?
 
Out of curiosity what risks are involved with just switching off the MCB for heating and testing for absence of voltage of the live wire and then working on that circuit?
Well, as with many things electrical, not many risks if all is well, but,

as Terry said, the MCB only disconnects the Line conductor and any unknown faults can result in other conductors becoming live.
 
Why does it have 'leave immersion off'?
Surely the immersion heater has it's own isolator switch next to the hot water cylinder?
 
Why does it have 'leave immersion off'?
Surely the immersion heater has it's own isolator switch next to the hot water cylinder?

At a guess it is to prevent other family members wasting money using the immersion heater when using the gas boiler is three times cheaper.
 
At a guess it is to prevent other family members wasting money using the immersion heater when using the gas boiler is three times cheaper.

Correct. The immersion has its own isolator switch but where it is located it often gets accidentally knocked and turned on. It's now turned off at the MCB to prevent it from being accidentally being turned on.
 

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