I just remembered something else I once saw, and that was a Hoover Turbopower junior which had been given 3-core flex. Someone had connected the earth wire to the handle. I forget why the cleaner had been bought in to me, but it was a routine issue like a belt or whatever else, rather than the fact that when plugged in it caused the RCD on the fuseboard to trip. Well it did in my shop anyway. The reason for this was because this model of cleaner was designed with a set of resisters connected to the netrual wire of the cleaner. This was then secured to the metal handle, in the trunnion area. I am not at all sure how it all worked, but it was done to take static electricity away from the handle and must have had just a tiny amount of current going through the handle. Static had been a problem for the Turbopower Junior on the first models and this system had been implimented to overcome the static.
Connecting the handle to the mains earthing system meant that the current from the Hoover-designed wiring was being taken down the mains earthing. Tiny as it may have been, it was enough to cause the RCD on my fusebox to trip. While I cannot recall the exact answer from the customer, I did ask if her home had a modern RCD, and she said she thought not, which would explain why it probably worked in her home.
