Main Grounding System Question

[AggieEE07]

I came across a grounding diagram different from what I would normally expect and wanted to get some opinions on the situation. The building's grounding system is shown to be bonded from the MGB (main ground bus) to the pad mount service transformer's ground triad. Under normal operating conditions some of the unbalanced neutral current will flow on this bond because it is in parallel with the service entrance neutral conductors, but the current will be minimal. This also should not have any effect on ground fault sensing because the main bonding jumper should be installed upstream of the current sensors.

Are there any problems under a fault condition this could cause with the building or transformer grounding? Personally I see no use for this bond and by removing it will improve the overall system design.

What are your thoughts?

 

[alehman]

It should probably be removed if this facility is under National Electrical Code jurisdiction. It's generally poor practice for the neutral current to be shared on a grounding conductor. Obviously first verify the grounding system that will remain is correct.

Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[pwrtran]

Basically your non-current carrying conductor will carry current on both normal and fault conditions. It may:
1) cause noise signals on some sensitive electronic devices as the ground potential is no longer zero
2) screw up the sensitivity of the ground fault protection