Problems with immersion heater MCB

[BotleyDave]

Hi Everyone,
I've just fitted a new immersion heater wired to a new MK 20amp water heater switch. This in turn is connected to a 16amp MCB on a Wylex board. The problem I have is every time I switch on the heater at the switch both RCDs on the Wylex board trip. I've tried another switch with the same result and also tried connecting to another spare 16amp MCB with the same result. I then connected to another spare 32amp MCB and the heater worked. My question really is am I OK to do this as a long term option or should I get a new Immersion heater. Many thanks BotleyDave

 

[kbdiy]

Being a simple lad at heart and not an electrician I would hazard a guess that trying to pull 20amps through a 16amp breaker was bound to trip it.

Can you not get a 20amp breaker?

 

[AndyPRK]

What caused you to fit a new imersion heater?
Has this happened since the new CU was fitted? or wiring changed inside?

I would check that the neutral connection for the immersion is taken from the correct neutral bar.

The fact that both RCD's trip, it sounds like its on the wrong one !

Was the 32A MCB on the other side of the board ? i.e other RCD

 

[flyingsparks]

Sounds like your neutrals are on the wrong neutral bar.

 

[BotleyDave]

Thanks Andy,

I've just checked and I did wire the neutral on the wrong side of the board. I don't know why I did that and then didn't think to check. Everything is now working fine.

Thanks again.

BotleyDave

 

[JohnW2]

Being a simple lad at heart and not an electrician I would hazard a guess that trying to pull 20amps through a 16amp breaker was bound to trip it.

It's the switch which is rated at 20A (maximum), not the immersion heater - which (assuming its a 3kW one) will take about 13A - fine on a 16A MCB.

In any event, you really should read the question properly before replying. It was two RCDs which were tripping (for reasons now revealed), not the 16A MCB!

Kind Regards, John