You've reminded me of something, BRL. Not computing, but SD's a very patient guy.
Notoriously short-tempered mate was installing quite expensive cordless telephone system in his warehouse. Ran an extension lead to the 'command centre' for all the phone extensions.
Mounted same at various stragegic locations throughout the building. Switched on - nothing. Tried extension in another wall socket - nothing. Plugged something else into both wall sockets - worked fine.
Totally lost control and smashed command centre to pieces.
When I checked later, the fuse in the extension lead plug was blown.