9.5kw Galaxy unvented heater trips RCD

[esalglop]

When water is turned ON the RCD TRIPS.
10 metres from CU, 40A mcb. 10mm Doncaster Cable.
Changed to 50mcb and 25mm meter tails. still RCD trips?

 

[James]

I R test the element,
bet it has failed.

corrosion makes a small hole in element case and lets water in.

 

[Zerax]

I thought he meant when he runs the tap !!

No wonder I was confused...

 

[esalglop]

This is brand new Galaxy from Screwfix. This problem occurred. Could not find any faults so returned. It is only with replacement thatI query there cannotbe two faulty units, however, tests with multimeter all OK, so E TO L reads 0mV, so replace 10mm cable with 25mm meter tails and replace 40mcb with 50 mcb but that I agree is silly as it is an Earth leakage problem to switch the RCD.??
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BTW, i have been installing CU, lighting and ring main circuits for 50 odd years. WHEN I had completed the whole circuit (I test each socket with SocketanSee) Then get friend sparkie to test and sign work off.

 

[James]

this is a simple element with a pressure switch to turn it on.
i still think that an insulation resistance test on the element will guide you to the problem.

 

[esalglop]

Yes Zerax. Problem only occurs when tap is turned on.
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I have placed the black cap on E and red cap on element. Testing with Multimeter between these two points reads 3M ohms

 

[James]

that is a poor result for a new appliance, a multimeter is only testing at very low voltage.
I expect that a 500V I R test between element and earth will give awful result. (disconnect incoming supply first)

 

[Wilko]

Hi - as per James - safely isolate the circuit, disconnect the incoming L and N to the heater and confirm your results.

 

[esalglop]

So I have returned to the unit black lead on end of element
Neutral) red on Earth 3 Mohms.
I then put Black on Earth red on Neutral 0.00 ohms
Massively confused, so I checking CU
same result N toE = 3M ohms
E to N - O.00 ohms
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Disconnect Neutral to Galaxy. O/L reading on N to E or E to N.
Does this mean that there is fault in cabling to CU.
TOOK meter tails out of CU attached direct to Galaxy and it worked!,,,?
What the devil should I be suspecting.

 

[James]

I think at this point, you should be getting a local electrician involved.