It's always a 'friend' who does this kind of stuff...
A friend of mine (we'll call him Gary, for that is his name) was trying to work out why the electricity on the upper floor of his mother's (Doreen) house had suddenly and mysteriously quit working. The house was in London, England and had been the family home for close to 25 years at the time of the incident. Please remember that standard electricity in my part of the world is single phase 240 volts
The entire upper floor, 3 bedrooms, a bathroom and landing, plus the laundry annex (tacked onto the back of the house) with a washer, drier and several sockets on a workbench was connected to an unswitched fused spur in the cupboard under the stairs which in turn had been spurred off the light fixture (without bulb) in that same cupboard.
The problem came to light (no pun intended) when Gary's mother decided to put a light-bulb into the fixture in the cupboard under the stairs and switched the light off.
It turns out that Gary's late father (Tony) was no electrical genius - Although his makeshift set-up had been working faultlessly for at least 3 years following his death from unrelated causes.
Tony (had he been alive at the time) would have argued that the fused spur was a major safety feature. However his argument would have been completely pointless when it was discovered that the standard 13 amp fuse had been replaced with a piece of broken screwdriver.
Names and locations have NOT been changed to protect the innocent. Happy St Pat's Day, Tony - you were a fine Irishman