Here is my dilemma. Picture this arrangement: a system with a 100A three-phase supply will have a RCD incomer (and possible some generator transfer switch in the future). As well as the SWA supply cable's earth there will also be some lightning protection so a few earth rods as well. From the distribution board there will be around 4-6 single phase UPS, of 3-5kVA each, and they will be distributed over all 3 phases vaguely tiring to keep the load balanced.
What worries me is when the RCD trips (testing, if nothing else...) or the transfer switch is going between mains and generator, the neutral to the board will be disconnected and floating. But the UPS will still be powering everything (after all, that is their job) and it bothers me that we might see the neutral getting to 50V or 100V and so one phase going over 300V with respect to earth depending on the leakage currents and how they might balance (or not). In the past those UPS show 10-20mA each.
My first thought was to put something like a indicator lamp between neutral and earth to:
TL;DR: Is putting a small lamp between N and E prohibited?
What worries me is when the RCD trips (testing, if nothing else...) or the transfer switch is going between mains and generator, the neutral to the board will be disconnected and floating. But the UPS will still be powering everything (after all, that is their job) and it bothers me that we might see the neutral getting to 50V or 100V and so one phase going over 300V with respect to earth depending on the leakage currents and how they might balance (or not). In the past those UPS show 10-20mA each.
My first thought was to put something like a indicator lamp between neutral and earth to:
- (a) act as a warning that something odd is up (i.e. significant N-E voltage), and;
- (b) keep the neutral below 10-20V w.r.t. earth if only tens of mA unbalanced leaking when the neutral is isolated.
TL;DR: Is putting a small lamp between N and E prohibited?
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