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Cause of electric shower failure


 
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williaminsurrey

from United Kingdom

Joined: 08 May 2007
Posts: 15
Location: Surrey,
United Kingdom

PostPosted: Wed Apr 10, 2013 5:26 pm Reply with quote

Hi Experts,

My Mira sport max 10.8kw shower gave up the ghost last week. When I turned it on for the last time there was a loud ‘pop’ or ‘bang’ then shower went dead (panel lights went off). What worries me is that the RCD that supplies the shower (Wylex, 80A, 30mA) didn’t trip. I have since tested the RCD using the yellow button on the RCD itself (simple test, I know) and it seemed to work fine.

So my question is: What kind of catastrophic failure in the shower would not cause the RCD to trip?

A bit more information. There was some brief warning that something wasn’t right with the shower. About an hour before the final failure, water started flowing from the shower spontaneously without me turning it on (although there was power to the shower). The flow did eventually stop after a few minutes, although my pressing the ‘off’ button didn’t seem to have much effect. I later took off the front cover and couldn’t see any obvious signs of water ingress or electrical failure (see photo).

Thanks for any help.
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viewer

from United Kingdom

Joined: 02 Apr 2005
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PostPosted: Wed Apr 10, 2013 5:42 pm Reply with quote

Failure is on circuit board which has working parts which are not directly connected to the mains supply. A small transformer turns the 230V to whatever is needed on the board (maybe 5 - 24 V) No idea what went wrong, but a capacitor failing can make an amazing bang for such a small item. There would be no danger. If the failure had caused a short to neutral or earth then the MCB or RCD would have tripped.
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Robin0577

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PostPosted: Wed Apr 10, 2013 6:22 pm Reply with quote

I would agree with something on the printed circuit board having gone pop.

Usually there is evidence, i.e. scorch marks or debris and often an unpleasant smell, so I would assume it's something on the far side of the board we can't see in the picture or possibly even on a second board underneath?
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JohnW2

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Joined: 28 Jan 2011
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PostPosted: Wed Apr 10, 2013 6:30 pm Reply with quote

williaminsurrey wrote:
My Mira sport max 10.8kw shower gave up the ghost last week. When I turned it on for the last time there was a loud ‘pop’ or ‘bang’ then shower went dead (panel lights went off). What worries me is that the RCD that supplies the shower (Wylex, 80A, 30mA) didn’t trip. I have since tested the RCD using the yellow button on the RCD itself (simple test, I know) and it seemed to work fine.
So my question is: What kind of catastrophic failure in the shower would not cause the RCD to trip?

I take it that the MCB protecting the shower circuit didn't trip, either? In addition to what viewer has said (very probable answers), there are plenty of catastrophic things that could happen which would trip an MCB but not an RCD - only a fault allowing current to flow from live to earth would cause an RCD trip. A fault from live to neutral would trip the MCB, but not RCD.

Kind Regards, John
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RF Lighting

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PostPosted: Wed Apr 10, 2013 8:51 pm Reply with quote

Assuming there is an MCB of course icon_wink.gif
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JohnW2

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PostPosted: Wed Apr 10, 2013 9:00 pm Reply with quote

RF Lighting wrote:
Assuming there is an MCB of course icon_wink.gif

Indeed so. We've seen a good few examples of 'shower CUs' fed straight from pre-CU Henleys which contain pretty RCDs and nothing else!

Kind Regards, John
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williaminsurrey

from United Kingdom

Joined: 08 May 2007
Posts: 15
Location: Surrey,
United Kingdom

PostPosted: Wed Apr 10, 2013 9:41 pm Reply with quote

Thanks for all of your replies - very helpful. Yes, the shower is fed by a Wylex 50A MCB, which didn't trip.
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