Only receiving 10v on shower main


Postby Burrito Boy » Sun Jun 06, 2010 8:09 pm

Hi all,

I was hoping someone here may be able to help me. My electric shower recently stopped working and I'm having trouble fixing it. In the past it has been caused by a loose connection in the pull switch unit, but this time all of the connections have been fine. So, I decided to investigate the problem with a multi-meter, and found that apparently the pull-switch for the shower is only receiving 10v from the MCB (which obviously isn't enough to power the shower).

This is really puzzling me, can anyone offer a cause or solution as to why only 10v is coming from the MCB?

Thanks!
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Postby kbrownie » Mon Jun 07, 2010 11:34 am

is the MCB faulty, do you have a loose connection at the CU, any damage to cable along it's route.
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Postby Burrito Boy » Tue Jun 08, 2010 11:59 am

Thanks for your reply, but somehow I managed to fix it last night.

I tested the MCB and found it was providing 230v, then reconnected the shower and it worked! It had me puzzled but at least it's fixed now.
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Postby ericmark » Tue Jun 08, 2010 12:43 pm

Depending on how measured 10 volt could be a full disconnection. Inductance and capacitance can be enough to register volts with a meter with a high ohms to volt impedance/resistance and with modern electronic meters they act like old valve voltmeters taking little or no current.

So you should consider 10v as being 0 volts unless measured under load.

Breaks can be found with a number of methods:-
1) The calculated guess. You look at devices and joints and test there.
2) Inductance finders and like. They measure magnet effect and can but run up and down wall.
3) Step by step testing. Starting at CU and moving towards the shower.
In practice one uses them all. But the big thing is what to measure to? Clearly if the problem is in the neutral measuring to earth may give false reading, Also there could easy be 10 volts between neutral and earth so one can get some odd readdings.

Although I don't like neon screwdrivers used with knowledge they can help work out if a neutral or line fault.

However there is no quick fix or crystal ball it often is just a methodical moving away from source until the fault is found.

However although under current regulations the supply to a shower should be RCD protected there is no guarantee there is a RCD or that it will work within the 40ms allowed or at 30ma so even the best electrician can make a mistake so do ensure your not on your own while looking and the other person does know what to do if anything goes wrong.

Do remember if the fault is due to lose cable it could jump out and bite you?
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