RCD didn't!

John · 2010-12-31T16:27:38+00:00

Switched on the power to the pump in the garden pond now the ice hasthawed but nothing happened. Put hand into water to lift pump out to seeif was blocked and got an electric shock (strong tingle).Switched off power and recovered pipe to find the mains cable had becomesevered under the water - whether this was because the ice had cutthrough it or one of the squirrels had chewed it whilst it was above thelevel of the ice....Anyway the RCD was not worried - ooh err! Will double check the earthconnection to the pump when I replace the cable.

Dec 31, 2010 28 Replies

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Dave Liquorice 15 years ago

Well connected to earth, ie sticking you hand in dirty pond water will connect you very effectively and the body can detect pretty low currents when well connected. Mostly our skin resistance is fairly high so we don't feel the "tingle" from most other electrical sources like batteries etc. Not really surprised the RCD didn't object.

I well remember getting "Ouch, WTF!" shocks from the DC on an ordinary telephone line (50v, current limited) when putting the lines on for an outside broadcast, standing in a puddle in the pouring rain.

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Tim Watts 15 years ago

I take it he lived to form a scientific conclusion of his experiment :)

Happy New Year!

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Andy Dingley 15 years ago

A moulded pond liner has a very high earth impedance, if there are no other paths round it.

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F Murtz 15 years ago

Maybe he could set it all up again with a meter in circuit and stick his finger in again. (just kiddin )

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Tabby 15 years ago

That all sounds good for the situation where only the live is exposed. When you've got L&N together, the electric field around them will be reduced, so I'd expect the curent for L to the earth under the pond to be nearer half this.

Then there's the L to E flex current. If we make a rough estimate for a pair of razor blades in clean water of 5A, 1mm^2 would get around

8mA, for a total L-E leakage of about 15mA.

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Mike Clarke 15 years ago

Whether or not the OP was wearing wellies could also be significant.

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Andy Dingley 15 years ago

Earthed sausage on a stick.

I once tested the plasma cutter's flesh-eating abilities with a couple of old barbecue sausages and a worn-out welding glove. It was quite reassuring to find that it doesn't cut "flesh" at all well.

Sausages do have a much lower impedance than the standard assumptions for flesh, but it's near enough for this.

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Skipweasel 15 years ago

Considerable capacitance to ground, I expect. ICBA to work it out.

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ARWadsworth 15 years ago

Plug the thing back in and tell your MiL that you have dropped your watch into the pond and ask her if she could be so kind as to retrieve it for you.

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