NEC code violation

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hhlst11@verizon.net

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We have a separately derived system consisting of two 750 KW diesel generators that automatically start and parallel via a paralleling switchgear. Each generator is configured as a grounded wye source that feeds the switchgear via 3-wire plus ground (no neutral wire leaves the generator). Each piece of equipment is grounded through a ground bus connected to earth via a grounding electrode. Through automatic transfers switches (ATS) the paralleling switchgear feeds 3-wire loads, one of them is a UPS with a built in zig-zag transformer. At the ATS the ground is not switched. Without getting into a long story, a group of engineers decided to disconnect the neutral bonding jumper at each generator because they thought it was causing the UPS to trip offline due to intermittent ground faults. Well investigation revealed that the tripping only occurred with utility power and not from the generators. The effects of removing the neutral bonding jumper at the generators causes syncing problems with the oncoming generator.
Can you clarify if having this neural bonding jumper disconnected is a safety concern (NEC code violation) or just an operational issue. Note that we hired two consulting firm and each came back with a different answer, one said safety NEC code violation and the other said it is a NEC code operation issue. I think it is a safety violation since a fault current has to travel through a distant grounding electrode (70 ft), through earth (clay), and eventually reaching the source (generator). This might cause a delay in the generator's breaker to clear the fault.

Thanks!
 
By your post I assume there are generator circuit breakers in the paralleling gear and at the generators?

The generators are matched units?

At the ATS the ground is not switched.
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You said the distribution is 3 phase 3 wire, yet you mention switching the ground, do you mean the neutral/grounded conductor or the Equipment Grounding Conductor (EGC)/"ground" which is basically impossible to switch?
 
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If there is no neutral to comes through to the paralleling SWGR from the gens, and the gens are 4W, then the N-G bond needs to stay at the gens.

Do not attempt to switch the equipment ground conductor and of course you have no neutral to switch anyway.
 
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