RCDs tripping feeding Megaflo heating elements

[2BobSparky]

Got 2 32A RCDs in a CU, each one feeding a respective Megaflo water heater circuit.

At the Megaflo each stat head is wired back through a timer and onto a fused spur. RCD is tripping straight away with cables connected to the stat and stat into element. Dissconnect stat from element and it doesn't trip the RCD.

IR on element gives me 0 between conductors and > 275M Ohms conductor to earth spade.

Originally we changed both heating elements and stats, but the RCD is still tripping immediately. It would appear the fault lies with the element/s but they're brand new!

 

[Bobster]

Sigh, N>E?

Edit: Didn't see that they could well be RCBO's, what KW rating are the elements?

 

[Pete999]

RCDs or RCBOs

 

[cobrauk]

Is this a new install ? if so Did you by chance mix the neutrals from the 2 circuits ?

 

[Darkwood]

The issue will be a simply one and one you will have overlooked, the problem for us if you have overlooked it then you will not have given us all the relevent info for us to see the issue ... can we clear up a point - you say you disconnect the stat and the rcd don't trip, when you disconnect the stat have you connected the elements direct without the stat in the loop or just left the circuit open....

Also are we sure the voltage and rating of the elements is correct for the supply your using?

 

[2BobSparky]

Is this a new install ? if so Did you by chance mix the neutrals from the 2 circuits ?

RCBOs and no not a new Install but thE flat had b een empty for some time.

 

[Darkwood]

Have you tested the whole circuit - cables inclusive? ... has damp creeped into the circuit somewhere?

 

[2BobSparky]

... can we clear up a point - you say you disconnect the stat and the rcd don't trip, when you disconnect the stat have you connected the elements direct without the stat in the loop or just left the circuit open....

Also are we sure the voltage and rating of the elements is correct for the supply your using?

no I haven't connected the active and neutral directly to the spades on the element if that's what you mean. I'm sure the RCBO will trip immediately if I do this as it does so as soon as the stat is pushed in with said cables connected.

2.7-3KW single phase element with a 32A RCBO..

 

[Octopus]

Are you saying that 1 x megaflow, 2 x immersion circuits, each supplied by seperate circuits, off seperate RCD's??

Do both RCD's trip?

Just asking

 

[2BobSparky]

Are you saying that 1 x megaflow, 2 x immersion circuits, each supplied by seperate circuits, off seperate RCD's??

Do both RCD's trip?

Just asking

Yes sir, that is the situation.

Problem solved now, turns out the sub circuit tales had been swapped around in the CU!

thanks for everyone's suggestions and advice!

 

[cobrauk]

I told you that ages ago didn't I ?

But if it was an existing circuit why wasn't it doing it before ?

 

[TJ Anderson]

Problem solved now, turns out the sub circuit tales had been swapped around in the CU!

Yeah, because that happens all the time doesn't it haha. The wires in existing installations get bored and just swap themselves over lol (neutrals are notorious for having a swap around to the other bar as the grass is greener over there). It happens on light fittings too, the switch wire sleeve disappears and the confused switched live jumps in the neutral terminal cause it looks the same, again all by itself. Good job you replaced all the elements, stats and whatever else anyway, Im sure that was appreciated. Well done you.