grounding question

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mshields

mshields

Senior Member
Location
Boston, MA
I'm designing a 13.8kV switchgear building at a hospital. The gear will be owned by the customer and contain utility primary metering in it. This switchgear will feed existing pad mounted transformers which then in turn feed existing hospital 480V distribution system, etc.

Into this building, I need to bring a 480V service for lights, receptacles, a heat pump for heating and cooling the building and various sundry things.

I know that when I bring a service like this to another building to provide a ground rod for that service but not to bond the neutral to ground at that point.

I also will be providing a triplexed ground rod system for grounding of the 13.8kV incommingt service. For this I'm employing a grounding bar on the interior wall of the building.

Here's the big question, do I connect my grounding electrode system for the low voltage system to my grounding electrode system for the medium voltage system.

On the one I am concerned that if I don't do it, I could create a situation where there are two potentials on two separate grounding systems.

On the other hand, I wouldn't normally connect the grounding system from the dela side of my transformers to my service grounding electrode system.

Not sure what to do?

Thanks,

Mike
 
D

DavisIMI

Member
I don't have a PE but I do have a CE, and I thought that all gec were to be bonded together for a single building or system.
 
J

jghrist

Senior Member
The grounding systems should be bonded together to eliminate any potential difference between them. This is the normal practice in the US, but in Europe, there are systems where the grounds are isolated, but care is taken to ensure a satisfactory distance between the grounding systems.

On the other hand, I wouldn't normally connect the grounding system from the dela side of my transformers to my service grounding electrode system.
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I'm not clear on this. Wouldn't the EGC on the primary side be connected to the transformer tank ground? The secondary neutral is also bonded to the transformer tank and to the grounding electrode. This would connect the two grounds together.
 
A

anbm

Senior Member
mshields said:
I'm designing a 13.8kV switchgear building at a hospital. The gear will be owned by the customer and contain utility primary metering in it. This switchgear will feed existing pad mounted transformers which then in turn feed existing hospital 480V distribution system, etc.

Into this building, I need to bring a 480V service for lights, receptacles, a heat pump for heating and cooling the building and various sundry things.

I know that when I bring a service like this to another building to provide a ground rod for that service but not to bond the neutral to ground at that point.

I also will be providing a triplexed ground rod system for grounding of the 13.8kV incommingt service. For this I'm employing a grounding bar on the interior wall of the building.

Here's the big question, do I connect my grounding electrode system for the low voltage system to my grounding electrode system for the medium voltage system.

On the one I am concerned that if I don't do it, I could create a situation where there are two potentials on two separate grounding systems.

On the other hand, I wouldn't normally connect the grounding system from the dela side of my transformers to my service grounding electrode system.

Not sure what to do?

Thanks,

Mike
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Where do you bond triplexed ground rod system to? To secondary of pad mounted transformer? (assuming 13.2kV/480V XFMR)

Which point is your main service entrance board of the building? Is it the MV gear or 480V board downstream of MV gear?
 
mshields

mshields

Senior Member
Location
Boston, MA
all of your input

all of your input

thanks for all of your input. I think my conclusion is this:

Whoever said that the systems would ultimately be connected together via the transformer case is I believe correct. But despite that being true, I don't think I want to leave it to chance that there be two separate grounding systems not interconnected. I think the key thing here is that I not bond the neutral to ground on the 480V service to this building.

But I agree that the two grounding electrode systems need to be tied together. i.e. they need to be one. I'll welcome anyone poking holes through this.

thanks,

Mike
 
walkerj

walkerj

Senior Member
Location
Baton Rouge
This is way over my head, but:

To me, it seems that if the two systems weren't bonded together,then if for some reason a 13.8 line somehow contacted, say, the metal conduit for a 480 volt feeder, no OCPD would operate.

Or am I way off:-?

Sorry to threadjack:smile:
 
B

benaround

Senior Member
Location
Arizona
mshields said:
thanks for all of your input. I think my conclusion is this:

Whoever said that the systems would ultimately be connected together via the transformer case is I believe correct. But despite that being true, I don't think I want to leave it to chance that there be two separate grounding systems not interconnected. I think the key thing here is that I not bond the neutral to ground on the 480V service to this building.

But I agree that the two grounding electrode systems need to be tied together. i.e. they need to be one. I'll welcome anyone poking holes through this.

thanks,

Mike
Click to expand...

250.30(A) and 250.30(A)(3) and 250.30(A)(7) deserve a look.
 
Smart $

Smart $

Esteemed Member
Location
Ohio
mshields said:
... I think the key thing here is that I not bond the neutral to ground on the 480V service to this building.

...
Click to expand...
I don't see any reason for concern here. We common-electrode ground these systems in powerhouses and industrial facilties all the time.
 
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