I can't blame a fellow spark for this but some of the previous work was dubious to say the least.
I got a call to a pub that had previous evidence of a rat invasion and they had chewed through the cable supplying the outside lights under the floor space in the first floor.
Yesterday whenever the hand dryer was switch on it tripped the RCD. IR test showed a short on all three wires. Followed it back from the gents roof space above to discover this. Ehmmm nice wires says Mr Rat! My understanding is that vermin will chew through anything that blocks their path, rather than the thought that they are simply sharpening their teeth. The hand dryer was spurred off the lighting circuit for the toilets, neither the cable or the breaker were spec'd high enough to handle the power of the dryer anyway.
At first it wasn't really obvious that the chewing had happened until you pulled the wires back through the hole in the wall. What gave it away was the black marks all over the cable that something had been passing back and forth. The hole leads back under the living room floor for the accommodation above the pub. So I by passed the dodgy part of the cable back to the CU with a temporary cable, until the laminated floor can be lifted next week to see what lies beneath? My Jack Russell is coming with me next week just in case!!