Source Breakers 3 pole or 4 pole

What type of neutral fault do you consider might give rise to a dangerous situation?

Greg L

I certainly hope you have adequate transfer switches on your standby and grid power source.

Your connection is a common practice, in that 3 phase systems normally draw power from the A,B,C phases and not from earth (N). The Earth (N) should generally not be a load bearing element, but a safety ground. This will usually show up as a lighter gauge wire for the neutral, and often bare wire. ie: you have a neutral grounded system.

The intent is to keep the phase to ground potential as low as possible, hence the "bolted" grounds. Any phase fault to ground will cause a trip in the breaker and remove the power source from your grid.

As additional protection some breakers are fitted with ground fault detection that will remove the phase power if current is detected in the neutral earth conductor.

Grounding systems for total shock protection is a science in itself, especially as one considers health care facilities, where patients are often connected to equipment powered from the lines. There have been cases where a shorting portable vacuum has induced a voltage potential into the neutral at low levels, but has killed a patient on another floor that was "directly connected" to inadequately grounded and protected equipment.

That is useful question.

In factories above diagram is justifiable. beacause of need to change the power supply when factories were powered of.

And please see this link: http://www.criticalpowernow.com/pdfs/ClPwrAOLCase.pdf

for detail of 4 poles breaker application.

You state that the generators are "not permitted to parallael".

This indicates that there is some link between the breakers that permits only one to be closed at any given time. If not there should be. In effect, what I see is a transfer switch.

Since each system is properly grounded when connected, whats your problem?

I doubt there would be any significant differece in ground potentials if one ground were disconnected if both grounds are good.