Water and Electricity

[The_Scotty]

Got called yesterday from a customer in a panic yesterday.

The bathroom upstairs had sprung a (bad) leak. I'm not a plumber but was called to help in a panic ie switch water off, isolate leak etc meantime.

Anyway the water was following its normal course along the downstairs ceiling and out the light fitting.

The light was still on so I switched the MCB off at the board.

A little while after isolating the leak and stopping the flow of water I removed the light from the ceiling. The light has a 'bowl' type design with the rim of the "bowl" sitting flush with the ceiling and the connections inside the "bowl".

The connector blocks (L,N,E) were sitting in 1" of water.

Shouldn't the MCB have tripped itself as soon as water connected with the terminals?

 

[rebuke]

The MCB would trip if there was a short circuit. While water is a conductor, it isn't a very good conductor, so probably didn't allow more than 6A (assuming that's what the MCB was rated at) to flow through, hence the MCB didn't trip. The fact the light remained on implies there wasn't a complete short circuit, otherwise the light would have gone out.

If you had an RCD on the circuit, then that should have tripped much quicker, as there would almost certainly have been enough leakage to earth for that to trigger...