3P vs. 4P Transfer Switches and Separately Derived Systems

[mecojax01]

I've seen a very good Mike Holt graphic explaining generator grounding for separately and/or non-separately derived systems that also includes the related applications of 3-Pole vs. 4-Pole transfer switches, but am having trouble locating that information. Can anyone point me in the right direction to find that graphic again?

 

[ActionDave]

I don't know about the graphic but generally the only reason to switch the neutral is if ground fault detection is part of the building's power system.

 

[ATSman]

3P vs 4P transfer switches & GFP

3P vs 4P transfer switches & GFP

Not Mike Holt but this is what I got:

http://www.genconnex.net/index_htm_files/PT-6005-GroundingAC-1-en.pdf 6005 ½

https://www.google.com/#q=power+top...cal+information+from+cummins+power+generation 6006 2/2

http://power.cummins.com/sites/defa...hnicalpapers/PT-7016-P1-TransferSwitch-en.pdf 7016 part 1/3

http://power.cummins.com/sites/defa...hnicalpapers/PT-7016-P2-TransferSwitch-en.pdf 7016 part 2/3

http://power.cummins.com/sites/defa...hnicalpapers/PT-7016-P3-TransferSwitch-en.pdf 7016 part 3/3

 

[mecojax01]

Thank you for the links and responses. I wasn't really asking about ground fault protection or indication, my question is more concerned with when generators are or are not considered to be separately derived systems, and how that affects the neutral and grounding. Here is my understanding of how it works ... If a generator is considered a separately derived system, the neutral is bonded at the generator, the generator frame is grounded and the transfer switches are 4-Pole (neutral is switched). If a generator is NOT a separately derived system, the neutral stays isolated from the ground at the generator, the generator frame is not grounded (ie: no ground rods) and the transfer switches are 3-Pole (neutral is unswitched). Is this correct?

 

[dkidd]

Look at slide 5 of this


http://www.russelectric.com/wp-content/uploads/3_or_4_pole.ppt

 

[templdl]

Where are you planing on grounding your neutral, just once at the normal source or at both sources? If at both sources, why?

 

[iwire]

Where are you planing on grounding your neutral, just once at the normal source or at both sources? If at both sources, why?

If you need to use a four pole switch you will need to bond at both sources.

 

[templdl]

If you need to use a four pole switch you will need to bond at both sources.

To my point. With little or no application information there are a lot of implications.