Service and Utility Bonding

[billyzee]

Suppose I am designing a building with the service entrance electrical equipment on the top floor of a four story building. And suppose that the utility transformer is located outside at ground level.

The utility will necessarily make an N-G bond at the transformer secondary. And there will also be a N-G bond in the service gear on the fourth floor.

The building structural steel and concrete reinforcing are all bonded and made electrically continuous. In other words, the N-G bond at the utility transformer and the N-G bond in the service gear have two purposely made parallel paths. The first being the grounded conductor (neutral) pulled with the service conductors and the second being the structural steel.

I am curous to obtain opinions about the code implications of this situation and what alternatives are available.

 

[bphgravity]

Are you suggesting the secondary of the utility transormer is gorunded to a shared grounding electrode with the building service? This is not likely.

However, I know what you are trying to get at. Unfortunately, the code is rather vague on how to handle "parallel paths" on the LINE side of the service disconnecitng means. In fact, it is not a violation to have multiple grounded and bonded parts and components on the line side of the service disconnect and in most cases it is required by the code (250.92 for example).

The result of an arrangement as you describe could be determined to be a source of objectionable current. In that case, Section 250.6 can be used for guidance.

As a side note, I hope you are in compliance with Section 230.70(A)(1) having your service located on the 4th floor.

 

[cripple]

Service and Utility Bonding

It is my opinion this situation could not be implemented because the service disconnect is not installed in a readily accessible location, as required per 230.70(A)(1).
In New Mexico the service disconnecting means is required to be located at grade level and in a installed in a readily accessible location.

 

[augie47]

Locally, if you service entrance remained outside the building until entering the 4th floor, the service disconnect could be located there.
It is unusual in this area with any of the POCOs to have an grounding conductor installed to their transformer along with the grounded. As bphgravity states, the Code does little to address grounding on the LINE side of a service.
If you building steel meets the requirements of 250.52(A)(2) you could bond your service to the steel then to the CCE and other electrodes,

 

[Buck Parrish]

I agree with the others... And your conduit to the fourth floor would need to be covered in two inches or more of concrete.

 

[billyzee]

Thank you very much for the helpful responses.

The AHJ has approved the location of the service disconnect as described. Access to the service disconnect is a lot easier than it sounds and it is not really an issue with the AHJ. So compliance with 230.70(A)(1) is not an issue.

The service conductors are in conduit to the fourth floor. It is long run but compliant with 230.50.

I mostly was trying to get expert opinions regarding the parallel neutral paths. I don't have a horse in the race. I'm just an interested party trying to come to grips with something that seems odd and yes....probably should have been designed with a service rated disconnect down by the transformer and then pulling an equipment ground up to the fourth floor.

I'm just trying to determine if it should have been done or is REQUIRED to be done. I don't see how it's required based on length/protection of the service conductors or location of the service disconnect.

Anyway, thank again.

 

[LarryFine]

As mentioned above, the service neutral is often paralleled by its conduit on the line side, even when the meter and disco are nippled together.

If it really bothers you, you could always place the main disco outside at ground level, and use the neutral unbonded on the fourth floor.