I just got an electric shock off the kitchen sink. How did that happen? The sink isn’t an electrical appliance. I don’t understand it.
This is a problem with earthing – the connection with the ground which ensures that any current which doesn’t follow its intended circuit flows harmlessly to the ground, without using other conductors (like your body) as a shortcut.
The problem arises when exposed metal (sinks, pipes, metal casings) is somehow connected to a live electrical source. This can happen more easily than you might think; water is a good conductor of electricity, and so are damp or wet substances like plaster or grouting. The current involved is usually low, but enough to give you an unpleasant tingle in the part of your body that’s in the circuit – and if the current’s high, or you’ve got bare feet, the shock can be far worse or even fatal, especially if you’re standing on a wet floor!
(The current doesn’t even necessarily have to flow to the floor, if you’re touching two different metal objects – say, a kitchen tap and a sink – and one is earthed while the other isn’t.)
Fortunately, the problem’s relatively easy to stop; ensure that there’s a good earth connection between all pipework and other metal objects which runs to the earthing block in your electrical consumer unit. (The technical term for this is electropotential bonding or supplementary bonding.)
Pipes can be fitted with clamps (which look something like jubilee clips). First clean an area of the pipe with steel wool to make sure there’s a good connection, then fix on the clamp. After that, fix the earth wire (which should have a green-and-yellow insulating sleeve to identify it) to the clamp.
Baths and basins should have an earth tag, to which the earth wire can be connected using a nut, bolt and metal washers. Again, make sure the connection is clean and free of paint or enamel.
Fixed electrical appliances will likely have their own earth connection. If they have a metal case, the case should also be connected to the earth.
It may be that the wiring is already there and that one of the connections has either worked loose or corroded. If so, all you’ll need to do is clean it up or replace the corroded parts.
However, because this is a safety issue, we strongly recommend that you have the work tested by a Competent Person firm of electricians or other qualified person – and if you have any doubts at all about your ability to do the work yourself, get a professional electrician to do it. (See our article on domestic electrical repairs for more details.)