Quiz

[ebee]

Happy new year to all.
Here's a question related to a real life scenario of a few years back.
Electrician rewires house to modern standards.
In the kitchen a double pole switch feeding an external socket.
Therefore if external socket gets damaged or owners go on holiday and want to prevent socket use in their abbsence then all ok.
After 12 months customer rings electrician suggesting "that external socket must be faulty" . Pond pump plugged into external sockets has been tripping RCD lately.
Conversley using an internal socket and extension run thru window them pump runs ok.
Electrician begins holiday abroad tomorrow so asks another electrician to investigate.
On return from holiday Electrician contacts his pal. Yes he fixed it , new pump required but he got a big nip whilst investigating. Does not unplug pump, gently tugs flex to bring pump near to reach, lays down on lawn, grabs pump to get it out and gets a nasty belt, RCD trips.
Yes he should have unplugged it before beginning his fault finding.
Why did the pump run until he touched it?

 

[bernardgreen]

The water in the pond is not Earthed due to a plastic non conductive pond liner between water and the earth.

 

[ebee]

Absolutely correct Bernard. An earth fault in the pump motor caused the RCD to trip when connected to the external socket. All well and good. The problem was that the customers own extension was only a two wire job he had for years and of course it worked but not earthed. Pond liner like a plastic container held some 240v water. Which was ok till he laid down on the lawn and made himself earthy then touched the pump and water completing the circuit. He became the c.p.c of that circuit. The replacement pump failed similarly in a few short weeks so the customer gave up to “these cheap French pumps” and bought a UK one. I wonder if the pumps were of substandard make ?

 

[ericmark]

In around 1990 I returned to the UK to find RCD's everywhere at work, I cursed the darn things, as fault finding was hard, specially when not switching neutrals. Line - earth fault easy enough, it is the neutral - earth fault which causes the problem, as the voltage between neutral and earth can vary a lot, so bit of damp bread in toaster trips RCD when kettle is used.

In the same way as birds can land on the power lines and not be injured, so a plastic pond liner can insulate whole pond. Ups beat me to it.