Discuss Why am I getting a 420v supply from the power grid to my home when it should be 220v. All my applicances blew last night in the DIY Electrical Forum area at ElectriciansForums.net

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happyhippydad

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Classic symptoms of a broken N connection between supply transformer and yourself.
Call the emergency number for electricity supply company.
James, could you explain a little please? If the neutral is broken there is no return path so where does the 420V come from between L-N?
 

James

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Ok, for instance the transformer feeds 4 wire, 3 phase and N down a row of poles a mile long, at the end of that run there are 3 houses.
Each house uses a different phase and the same N.
All works well, N is bonded to 0v , normally the star point of the transformer windings. max of 240v from the star point to each phase conductor

If the N cable breaks along that mile run, the houses at the end of the run are still sharing the same N connection but now it is not tied to 0v
Depending on what loads are connected to each phase, the N voltage will drift towards the phase voltage of the phase with the lowest resistance load on it.
The effect is that the N conductor voltage floats seemingly at random from 0 to 400v relative to a phase voltage. (0 to 240v relative to earth)

It is more common to happen in rural locations where the supply cables are separate and 1 can be broken without affecting the other cables, but it is not unheard of in towns etc.

If you end up with a farmer on the phone saying can you have a look at my electrics, the lights keep going bright and then dim as if they are possessed, tell them to turn everything off immediately before things start to go bang!!
 

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