Grounding and bonding

C

curious23

Member
Location
Ohio
Occupation
Electrician
I have a question.
I was working at a Fairgrounds that has 100 kva, Single phase padmoumt transformers that feed 200 amp 120/240 vac Load Centers mounted to Utility poles.
I found that the neutral and ground is bonded at the Padmount and they also had the neutral and ground bonded at the Load center with a grounding electrode(ground rod).
In my view this is a safety hazard, because of the parallel path back to the source.
I feel the neutral and ground should be separated at the Load center.
What is your opinion?
 
curious23 said:
I have a question.
I was working at a Fairgrounds that has 100 kva, Single phase padmoumt transformers that feed 200 amp 120/240 vac Load Centers mounted to Utility poles.
I found that the neutral and ground is bonded at the Padmount and they also had the neutral and ground bonded at the Load center with a grounding electrode(ground rod).
In my view this is a safety hazard, because of the parallel path back to the source.
I feel the neutral and ground should be separated at the Load center.
What is your opinion?
Click to expand...
The bonding should be done at both locations, but there should not be an equipment grounding conductor run between the two. Is there or is it just three wire between the transformer and the load center?
 
electrofelon said:
The bonding should be done at both locations, but there should not be an equipment grounding conductor run between the two. Is there or is it just three wire between the transformer and the load center?
Click to expand...
The bonding is at the Transformer. They do have 4 conductors ran from the tango box to the load center.
 
curious23 said:
The bonding jumper is a strap that connects the grounding electrode, transformer case and center tap.
Click to expand...
Ok so neutral and ground should be separate at the panel. As has been mentioned, there is an exception allowing it to be treated as a service with three wire used and bonding at each end. There would need to be no metallic paths between the two.
 
electrofelon said:
Ok so neutral and ground should be separate at the panel. As has been mentioned, there is an exception allowing it to be treated as a service with three wire used and bonding at each end. There would need to be no metallic paths between the two.
Click to expand...
Now suppose we have bonding at both ends, and the "neutral" and "SSBJ" are both the same size. Seems like an identical installation (other than color) to simply having parallel neutral conductors. Which would be allowed (with different colors) if both conductors were 1/0 or larger. [Bonus question: how many CCCs with L1, L2, N + N at 120/240V?]

Even if the SSBJ is smalelr than the N, putting it in parallel with N will not overload the SSBJ unless the N is overloaded. Because ampacity varies as diameter d1.5, but resistance varies as d2, so the first conductor to get overloaded is the larger conductor. Which wouldn't happen if the N is properly sized.

So while it's a violation of rules like parallel conductors and conductor coloring, I don't see any actual hazards from operation. [Wrong colors could be a hazard for maintence, etc.]

Cheers, Wayne
 
wwhitney said:
Now suppose we have bonding at both ends, and the "neutral" and "SSBJ" are both the same size. Seems like an identical installation (other than color) to simply having parallel neutral conductors. Which would be allowed (with different colors) if both conductors were 1/0 or larger. [Bonus question: how many CCCs with L1, L2, N + N at 120/240V?]

Even if the SSBJ is smalelr than the N, putting it in parallel with N will not overload the SSBJ unless the N is overloaded. Because ampacity varies as diameter d1.5, but resistance varies as d2, so the first conductor to get overloaded is the larger conductor. Which wouldn't happen if the N is properly sized.

So while it's a violation of rules like parallel conductors and conductor coloring, I don't see any actual hazards from operation. [Wrong colors could be a hazard for maintence, etc.]

Cheers, Wayne
Click to expand...
Yes sometimes it's just an issue of color and what we call it. For example I have a complaint about why we have to bring the grounded conductor to the service disconnect for a service, and can't just bring a ssbj like we can for an SDS. Really it comes just down to color and what we are calling it (ok, we might want it insulated if it's carrying neutral current).
 
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