The company I work for has just had a 5 kw electric shower installed into my flat. It has been installed as a spur to a 2.5 mm ring main. The ring main is not earthed. (Not unusual here in Jordan) The appliance is (I beleive) double insulated. I run several other appliances, including two electric blankets on the same ring. I have a feeling that this may be overloading the circuit (220V mains). If my calculations are correct, the shower should be installed as a direct line to the distribution board using 4 mm cable. The length of the run would be about 15-20 metres. Can you advise?
Rules and regs differ around world but we wouldn't do it in UK as 5000 / 220 = 22.73A, this may well be within the current rating of a 2.5mm cable depending on inst. method used, and as electric blankets only use a few watts circuit may not be over loaded.
As you say we would run a 4mm back to individual circuit on 25 A fuse/mcb mainly for volt drop reasons, but we do have toughest(safest?) system in the world, so maybe we worry a bit too much?
Hopefully theres an RCD on supply?
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