Grounding Generator System

I

ITFreestyle

Member
Location
California
Occupation
Engineer
I'm powering an IT server rack on an inverter generator, through UPSs. The transfer from mains to generator will be manual (unplugging equipment from home and plugging into generator; there will never be any connection between mains and generator). For safety, I know I should bond neutral to "ground" at the generator. This system should run nominally and be safe from "ground faults" inadvertently making equipment cases live/hot.

But the whole system is now floating. Should I connect the generator "ground" to earth ground in order to put the whole system at a known potential?

Note that there is equipment like cable modems within the rack that have earth ground connected to them via their coaxial inputs. But I don't think the ground potential gets from them to the balance of the equipment through ethernet cables and such. Nor are any of these cables heavy copper in any way.

What think you?
 
Deltaforce said:
250.30(A)(4) not allow float
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That is not the correct section 250.30(A) is for grounded separately derived systems and 250.30(B) is for ungrounded separately derived systems. Nothing in 250.30 tells you that you must install a grounded system.

You need to look to 250.20 for the requirements as to what types of premises wiring systems must be installed as grounded systems. We would need more information to say that the system is covered by 250.20(B) and required to be a grounded system.
 
don_resqcapt19 said:
That is not the correct section 250.30(A) is for grounded separately derived systems and 250.30(B) is for ungrounded separately derived systems. Nothing in 250.30 tells you that you must install a grounded system.

You need to look to 250.20 for the requirements as to what types of premises wiring systems must be installed as grounded systems. We would need more information to say that the system is covered by 250.20(B) and required to be a grounded system.
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Op used words
Home, IT rake, never any connection between mains and generator
Only grounded generator 250.20 and
250.30(A)
 
infinity said:
What does this mean bond the neutral to "ground"? Is the generator being setup as an SDS?
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By neutral to "ground" bond I meant connection between generator's chassis (equipment) and its neutral, at the generator source. Yes, SDS setup is preferred for this IT equipment. Since transfer is being performed manually, neutral is also being transferred from mains source. So I'm concluding that at least tentatively from what I've read, that the generator source should be earth grounded just like the mains source is. I'm not seeing any ground loops in what I've formulated.
 
ITFreestyle said:
By neutral to "ground" bond I meant connection between generator's chassis (equipment) and its neutral, at the generator source. Yes, SDS setup is preferred for this IT equipment. Since transfer is being performed manually, neutral is also being transferred from mains source. So I'm concluding that at least tentatively from what I've read, that the generator source should be earth grounded just like the mains source is. I'm not seeing any ground loops in what I've formulated.
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Is this a portable generator? If so the neutral to frame bonding is usually done from the factory and using it as a portable generator requires this.
 
ITFreestyle said:
So I'm concluding that at least tentatively from what I've read, that the generator source should be earth grounded just like the mains source is.
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So the portable generator (SDS) has an internal SBJ connecting the neutral to the frame and the EGC's. There is no connection to the premise wiring system. Your question is actually about the connection of the generator frame to a GES (grounding electrode system)? Is that connection required? For an SDS the answer is yes.
 
infinity said:
So the portable generator (SDS) has an internal SBJ connecting the neutral to the frame and the EGC's. There is no connection to the premise wiring system. Your question is actually about the connection of the generator frame to a GES (grounding electrode system)? Is that connection required? For an SDS the answer is yes.
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Agree. I think I've got it all. Thanks so much for the confirmation.
 
I don't think there is a guarantee that a portable generator has its neutral bonded to the generated frame. The neutral floats on my portable generator, but it is old. I think it needs to be bonded in this application if the server rack is inside a building, so you can bond the neutral to the frame if the manufacturer made that easy. Mine has no instructions for that and no obvious lug to do it, so I have a bonding plug that goes into one of the 30A twist lock receptacles that connects neutral to ground if needed.

I'd also read 250.34(A) GEC's to portable generators, and 250.94 Intersystem Bonding Termination Device (read for intent, as an islanded rack technically isn't a structure or building but you have the same issues).

Is this generator under 15KW? If so, its 15 and 20A receptacles should be GFCI protected. That is a secondary shock protection means in case things get energized somehow.
 
suemarkp said:
I don't think there is a guarantee that a portable generator has its neutral bonded to the generated frame. The neutral floats on my portable generator, but it is old. I think it needs to be bonded in this application if the server rack is inside a building, so you can bond the neutral to the frame if the manufacturer made that easy. Mine has no instructions for that and no obvious lug to do it, so I have a bonding plug that goes into one of the 30A twist lock receptacles that connects neutral to ground if needed.

I'd also read 250.34(A) GEC's to portable generators, and 250.94 Intersystem Bonding Termination Device (read for intent, as an islanded rack technically isn't a structure or building but you have the same issues).

Is this generator under 15KW? If so, its 15 and 20A receptacles should be GFCI protected. That is a secondary shock protection means in case things get energized somehow.
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Agree. I have to ensure the generator neutral is bonded to frame (and its L14-30R ground blade receptacle). I will look into the sections you mention for more insight as the rack is an island. Thanks so much.
 
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