Intriguing problem. Shower and Cooker tripping CB not RCD

[Andy C]

Opinions on this fault please, I have never come across this before.

Split RCD board with a shower (40 amp) and Cooker (32 amp) both on 6 mm T&E. Both are tripping the CB, apparently whilst switched off? RCD tested fine.

Shower is a 9.5kw, so feasibly the 40a might be a bit close to max, fed from a 45 amp pull switch.

Cooker is about 5.5kw so a 32a is fine, fed from a 45 amp double pole switch in a cupboard. The cooker is definitely tripping whilst switched off at the cooker? Not straight away but a few minutes later. No other load on circuit.

I haven't tested the appliances. Both are relatively new.

Both circuits have been tested from DB to isolating points at 45 amp switches and IR results were fine.

Thanks in advance for any suggestions.

 

[ashrow]

I would also be testing from isolators to disconnected cooker and shower.
Testing to the isolator is not the entire circuit.

 

[buzzlightyear]

loose connection. .

 

[DPG]

Is it the RCD tripping? If so then the fact that the current rating us near its limit is not the problem. Don't forget it could be a neutral to earth fault.
And cumulative leakage could be a factor.

 

[buzzlightyear]

I would also be testing from isolators to disconnected cooker and shower.
Testing to the isolator is not the entire circuit.

disconnected appliances and start and work form there .

 

[Deleted member 9648]

I'm confused, you say it's not tripping the RCD and yet you say RCD tested fine??
Why test the RCD if it's not that tripping? Also can you provide some clarification that the circuits are tripping their respective MCB's whilst the appliances are isolated?

 

[DPG]

Agree with above. Your post needs to be much clearer.

 

[telectrix]

cannabis farm in next door's attic, tapped into OP's electric.

 

[Deleted member 26818]

If an MCB that is protected by an RCD trips repeatedly, it would make sense to test the RCD just in case the RCD is not functioning.

 

[123]

@Andy C , Has any of this MCB tripping occurred when you are there?

 

[Andy C]

I'm confused, you say it's not tripping the RCD and yet you say RCD tested fine??
Why test the RCD if it's not that tripping? Also can you provide some clarification that the circuits are tripping their respective MCB's whilst the appliances are isolated?

Thanks for the reply. To clarify. The RCD is not tripping when the MCBs formthe cooker and shower trip out. I have done IR test to isolators from DB, readings all good.

The cooker mcb is tripping whilst the appliance is switched off on the appliance front.
The shower tripping might just be a coincidence.

I will test from the isolators to the appliances to rule out any fault there.

What I can’t get my head around is the cooker tripping a 32a mcb whilst switched off unless the appliance is somehow faulty.

 

[Andy C]

If an MCB that is protected by an RCD trips repeatedly, it would make sense to test the RCD just in case the RCD is not functioning.

The RCD is functioning correctly.

 

[Andy C]

@Andy C , Has any of this MCB tripping occurred when you are there?

No it hasn’t been reproduced when I am there which is annoying.

 

[Deleted member 26818]

The RCD is functioning correctly.

That was a reply to Wirepuller, who seems to think testing the RCD is pointless.

 

[snowhead]

The cooker mcb is tripping whilst the appliance is switched off on the appliance front.

Not on the Isolator on the wall, or wherever?
So the there is still a supply into the cooker casing?
Are there any obvious issues within the cooker, assuming the above 2 statements are true?

 

[Deleted member 9648]

That was a reply to Wirepuller, who seems to think testing the RCD is pointless.

It's a fair point.

 

[Deleted member 9648]

If testing has not found any issues I would be inclined to try replacing the MCB, I have known 'tired' MCB's to trip randomly before on light loading.

 

[Toneyz]

Just to clarify does these MCB's trip with the cooker and shower switched off but isolators switched on?
What is the insulation resistance in this state (note the caution L-N)
What make is the consumer unit & MCBs? open mind on the tired MCB's theory never experienced it myself not saying its a possibility on cheaper brands.

 

[Rpa07]

I experienced the ‘tired’ MCB on a shower circuit.
You go there armed to the teeth with test gear and after testing and proving good, disconnected at the shower, you knock your ladder and the MCB trips! Reset, tap the CU and it trips - I made the most of the situation and sourced the correct make MCB for the CU replacement instead of the BG that was fitted.
Granted this is the only time it’s happened so far but some things do come under the acronym K.I.S.S

 

[marconi]

What type of oven and hob are connected?