I have come across an unearthed neutral system in Algeria, wired under 1960's French regulations (which may well have changed by now).
This was an otherwise normal 3 phase and neutral system but the design called for a neutral earthing system which had a high resistance and an alarm so that the neutral was normally around earth potential but in the event of a Live- Earth fault, the alarm would go off, the neutral rise to 230V and the circuit remain in operation.
What had happened was that the Neutral Earth alarm unit was stuck in Customs and the system had been put into operation without it. The first fault had earthed one phase and subsequent faults had wither blown fuses and been found or, if they were in the same phase, had simply reinforced the earthing of that phase.
The idea that for months the system was operating with 400V Live -Earth on the other two phases is distinctly worrying.
I have come across an unearthed neutral system in Algeria, wired under 1960's French regulations (which may well have changed by now).
This was an otherwise normal 3 phase and neutral system but the design called for a neutral earthing system which had a high resistance and an alarm so that the neutral was normally around earth potential but in the event of a Live- Earth fault, the alarm would go off, the neutral rise to 230V and the circuit remain in operation.
What had happened was that the Neutral Earth alarm unit was stuck in Customs and the system had been put into operation without it. The first fault had earthed one phase and subsequent faults had wither blown fuses and been found or, if they were in the same phase, had simply reinforced the earthing of that phase.
The idea that for months the system was operating with 400V Live -Earth on the other two phases is distinctly worrying.
