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The maximum permissible disconnection time is 0.4 s in TN system. Why and from where this value (0.4 s) is obtained?
Former Community Member
The maximum permissible disconnection time in in the event of a short circuit between a phase conductor and a body or protective conductor or a protective-neutral conductor is 0.4 s in TN system. Does anybody know this value (0.4 s) obtains from where? How this value is obtained?
And on TT you'd not normally have the upfront earth fault relay or RCD set to the full 5 seconds, or anything like it, the problems are more likley on PME type supplies, where a fault in thre street can join L and N together, on the supply side, so your LNE at the consumer side all float up to some midphase voltage and no consumer side ADS operates.
There is a good reason for all hand held devices to be double insulated, rather than class I. You are very unlucky to be unloading the washing machine at the key moment, and also in contact with something connected to true ground but not locally bonded, while power tools hair dryers etc that are held tightly for long periods are all double insulated. Things that go outside, like hedge trimmers and lawnmowers would be especially risky if class I.
It is for this reason that car chargers are coming in for a lot of scrutiny, as they seem to be the only thing that breaks this rule, being designed so the car metal is at earth potential.
And on TT you'd not normally have the upfront earth fault relay or RCD set to the full 5 seconds, or anything like it, the problems are more likley on PME type supplies, where a fault in thre street can join L and N together, on the supply side, so your LNE at the consumer side all float up to some midphase voltage and no consumer side ADS operates.
There is a good reason for all hand held devices to be double insulated, rather than class I. You are very unlucky to be unloading the washing machine at the key moment, and also in contact with something connected to true ground but not locally bonded, while power tools hair dryers etc that are held tightly for long periods are all double insulated. Things that go outside, like hedge trimmers and lawnmowers would be especially risky if class I.
It is for this reason that car chargers are coming in for a lot of scrutiny, as they seem to be the only thing that breaks this rule, being designed so the car metal is at earth potential.
