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I have a European machine using a 480/400 volt three phase transformer. The neutral conductor is used to power some devices at 230 volt. The manuf. insists that the neutral must not be solidly grounded. I believe this creates an unstable electrical environment for the machine electronics also, it creates a shock hazard under ground fault conditions. Am I thinking correctly on this?

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The manuf. insists that the neutral must not be solidly grounded. I believe this creates an unstable electrical environment for the machine electronics also, it creates a shock hazard under ground fault conditions. Am I thinking correctly on this?

You don't use neutral for grounding. You use the protective earth, PE or earth point for grounding and, if you are conscientious, use an RCD on the circuit (GFCI in North America and elsewhere).

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I don't see a problem with floating part of the electrical system. Nowhere is it written that a conductor must be grounded; any common US/CA air conditioner or water heater does not have any conductors that are grounded, they are all 120V away from earth.

Of course if you are using consumer-ready products as part of the machine, you must assure they are listed for this use, i.e. their insulation is up to the task of a floating neutral and a line wire that may be farther from earth than expected. If you are providing receptacles for end-user use, that's a problem because they could plug something in which is not tested to that use.

Now if you are using a 3-phase configuration where one conductor is typically bonded to ground, and yours isn't, you might want to stop calling that conductor "neutral". A wye center could be called "center" and a wild-leg-delta midpoint could be called "midpoint".

Warning: bat-crazy language ahead. Neutral is a word which is slang for what the NEC lawyers call "GroundED conductor", which is defined as near ground because it is bonded to ground in one specific location. (Not to be confused with "equipment groundING conductor" which is your safety earthing and everyone calls "ground" or "earth".) Neither of which has anything to do with Vss or GND in the DC electronics vernacular.

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