shock from an appliance


Postby 333rocky333 » Wed Jan 16, 2008 6:46 pm

AS I mainly do commercial work .

With domestic, can any one explain Why does a metal kitchen sink/draining board not need supplementary bonding as opposed to a metal part in a bathroom,
Reason I ask
Someone told me they occasionally get shocks from the washing machine with Moulded Plug (earth continuity ok to casing) and it is worse if they also touch metal draining board (copper pipes , plastic waste) at the same time.
I realise they have a problem that needs sorting out,
But they seem to think it just needs bonding.
I disagreed and said kitchen does not have to be bonded.
They asked WHY?

As the main bond has not been located or verified
would bonding make the present situation worse , as I think It might.


The supply is pme
With the entire house all unplugged
The actual ring circuit including the washing machine point has low insulation resistance L to N of approx 1.5 megohms But L-E and N-E are in excess of 100megohms.E loop imp is 0.72ohms at the W/Machine point
This obviously needs investigating.
But could that put a voltage into the system earth causing there problem.


For my reference.

What is most likely, a problem with voltage in the electrical earthing or with some sort of voltage in the copper piping.

There is no visible main bond on the water and are in the process of organizing having a periodic inspection.
Thanks
333rocky333
Posts: 182
Joined: Sun Nov 25, 2007 11:03 pm

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Postby ericmark » Thu Jan 17, 2008 12:40 am

I was like you mainly industrial but for my 2 pennies worth.
I would suspect that an immersion heater, waste disposal unit, central heating boiler, motorised valve, tank thermostat or some other water connected item has an earth fault and no earth. And the washing machine is OK and earthing a fault from else where. I think you have already had same thoughts? Bits of plastic pipe do cause problems and I will guess you will find the sink is isolated from the main equipotential earth bonding conductor. I know in my house when the new shower was fitted plastic pipe was used. An earth link was fitted between the two metal sections but it seems that is not always done. Looking at IEE website on plastic pipes we get the following:-
“If there are no shoes and hands are wet, the impedance falls to 500Ωand the current at 230 volts is 460 mA. This is getting decidedly unpleasant. Immersion of the body in a bath, in effect halves the impedance of the body and current at 230 volts would then be as high as 1,000 mA. This is dangerous, and can kill.â€
ericmark


Postby HomeBrewPower » Thu Jan 17, 2008 2:31 am

333Rocky333,

I would as a first step carry out a ZE to confirm the property has an earth then Bond the Services.

1.5Meg Ohms NEEDS investigating as there is deffinately some earth leakage to phase. Assuming the property has either BS3036 Rewirable Fuses / BS EN 60898 MCB's then the fault will not automatically disconnect.

Sounds like the property needs an overhaul / rewire
HomeBrewPower
Posts: 3
Joined: Thu Jan 17, 2008 1:58 am


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