Neutral switching for parallel generator operation 1

[a10jp]

When you have parallel generator (emergency standby, permament installation) in operations, through a set of parallel switchgear, is there any special consideration that requires the ATS to also switch the neutral? In the case of a single emergency generator, I always prefer to solidly bond the generator neutral to neutral bus at the main dist panel, which is grounded at that point. In that case I can use a 3-pole transfer switch. But for parallel generator operation, is there something else to consider?

 

[ScottyUK]

Where is the generator neutral earthed? You need to avoid creating a path in parallel with the neutral conductor through the earthing system, otherwise neutral current will flow through the earthing system. If you do it will almost certainly be a code violation and will cause problems with your earth fault protection. A single bond between the system neutral and earth is necessary, but in a retrofit installation it is sometimes difficult to achieve.


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If we learn from our mistakes I'm getting a great education!

 

[a10jp]

For single generator scheme, I would connect the generator neutral to the main neutral bus at the service entrance. There you have a single bond to the ground for both the main distribution and the generator system and not separately derived.

 

[waross]

If you are able to connect all of your generator neutrals to the neutral bus in the main panel so that the one grounding point for the main panel serves all the generator then you may use three pole transfer switches.
If this is not possible due to ground fault protection issues or the distance from the generators to the main panel it may become real complicated, real quick.
If you have parallel generators connected to the bus by a contactor or breaker, it may be a challenge to arrange a system where the generators are grounded by the system when online, and still safely grounded when offline. In some instances you may need an isolating transformer.

Bill
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"Why not the best?"
Jimmy Carter

 

[a10jp]

Hi Bill, just want to say thanks for explaining. I think your suggestion for adding a isolation transformer should do the trick, where the isolation can isolate ground circuit. I need to think about this more. Thank you so much for the idea!! And thanks again for your explanation on this subject again!!

 

[Freeportpower]

Is this a UK application ?