RCD tripping intermittently when electric shower is on

My in-laws have a problem where the TCD on the distribution board trips occasionally when the electric shower is on. They have had the shower replaced and the new one also does the same thing. I assume this discounts the shower as the problem. I have asked them to disconnect all appliances and try again and again it sometimes is OK and sometimes trips. Any idea how I can investigate further? I come from a computing hardware background so have basic electrical skills and have a good multimeter!
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Ian


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x-posted to uk.d-i-y for more replies
Start off by reading
http://wiki.diyfaq.org.uk/index.php?title=RCD#Nuisance_trips
However I would guess that there is a neutral earth fault somewhere on one of the RCD protected circuits (not necessarily the shower circuit) and the high current that the shower draws is exposing the fault.
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Cheers
Adam



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wrote:

mounted switch feeding the shower.
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