Two switchboards

[hhsting]

That's an arbitrary view of those requirements
If xfmr was premises owned your clearly allowed to only bond at transformer.
The main bond location being required at two locations when the tap originated in an enclosure with a main bond is a ridiculously arbitrary interpretation. Electricity doesn't care what you call a service disconnect.

Nope main bonding jumper at service disco is required. AHJ will not allow. Would anyone else care to chime in?

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[Wire-Smith]

That's why I said get AHJ approval, 90.4 is an extremely important code section, the NEC is not perfect and they know it er'go 90.4

 

[Wire-Smith]

If AHJ won't allow that, the only other suggestion I have is the premises transformer

 

[Wire-Smith]

I mean it's a 480 277 service it would be easy to only have neutral loads downstream of a premises xfmr, it might already be that way

 

[hhsting]

I mean it's a 480 277 service it would be easy to only have neutral loads downstream of a premises xfmr, it might already be that way

Premise transformer is something that I cannot enforce. Thats a design issue can only suggest. Would have to check AHJ for sure utility xfmr bonding only. 95% sure would not be allowed.

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[Wire-Smith]

Premise transformer is something that I cannot enforce. Thats a design issue can only suggest. Would have to check AHJ for sure utility xfmr bonding only. 95% sure would not be allowed.

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Are there even any 277 loads? If not, the design already uses the premises transformer I want and you don't have the objectionable current issue. So long as its an isolation transformer with no neutral to the primary, which is highly likely

 

[hhsting]

Are there even any 277 loads? If not the design already uses the transformer I want and you don't have the objectionable current issue

Yes exterior swbd has 277V light loads, water heater load, space heater load, 480 to 120/208V transformer.

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[Wire-Smith]

What do they have (1) 20 amp 277 lighting circuit for LEDs, LOL. 277 Volt water heater? Or just lights, they could just use 480v lights. I don't know if you talk to the designer but it would only take a little rearranging and you wouldn't have any possible objectionable current. If they can eliminate the neutral loads on the service whether changing to other voltage equipment or using isolation transformer for the neutral loads.

 

[hhsting]

What do they have (1) 20 amp 277 lighting circuit for LEDs, LOL. 277 Volt water heater huh. I don't know if you talk to the designer but it would only take a little rearranging and you wouldn't have any possible objectionable current. If they can eliminate the neutral loads on the service whether changing to other voltage equipment or using isolation transformer for the neutral loads.

Lights include parking lot LED, office light LED, and high bay. Space and water heater I guess can be change to 208V or 120V.

They do have time clock 277V 20A(5), 277V exit wall lights 20A(3), 277V control panel 277V circuits 20(A)(1). Not sure can be change to 120V or 208V after transformer.

Now that leaves behind 480V three phase roof top units load but they are balanced.

Now in future anyone can just place new 277V load on the panel. I will ask them to place 480V to 480/277V isolation transformer after main breaker of exterior swbd. Is their any 480V to 480V/277V three phase 700kva iso xfmr?


Swbd #2 FP has no 277V load.

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[hhsting]

Lights include parking lot LED, office light LED, and high bay. Space and water heater I guess can be change to 208V or 120V.

They do have time clock 277V 20A(5), 277V exit wall lights 20A(3), 277V control panel 277V circuits 20(A)(1). Not sure can be change to 120V or 208V after transformer.

Now that leaves behind 480V three phase roof top units load but they are balanced.

Now in future anyone can just place new 277V load on the panel. I will ask them to place 480V to 480/277V isolation transformer after main breaker of exterior swbd.The secondary of xfmr would have to be grounded 250.30 GEC to bldg steel or water pipe ofcourse and need to comply per NEC 2014 Article 450.22. Would the grounding of the xfmr create objectionable current? Is their any 480V to 480V/277V three phase 700kva iso xfmr?


Swbd #2 FP has no 277V load.


Edit:


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[Wire-Smith]

Lights include parking lot LED, office light LED, and high bay. Space and water heater I guess can be change to 208V or 120V.

They do have time clock 277V 20A(5), 277V exit wall lights 20A(3), 277V control panel 277V circuits 20(A)(1). Not sure can be change to 120V or 208V after transformer.

Now that leaves behind 480V three phase roof top units load but they are balanced.

Now in future anyone can just place new 277V load on the panel. I will ask them to place 480V to 480/277V isolation transformer after main breaker of exterior swbd. Is their any 480V to 480V/277V three phase 700kva iso xfmr?


Swbd #2 FP has no 277V load.

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You can get a transformer for any possible setup. They may rather change to 480 equipment instead though

 

[hhsting]

You can get a transformer for any possible setup. They may rather change to 480 equipment instead though

In future anyone can just place new 277V load on the panel without knowing. Also, the secondary of xfmr would have to be grounded 250.30, bonding neutral to gnd and GEC to bldg steel or water pipe ofcourse and need to comply per NEC 2014 Article 450.22 over 112.5kva. Would the grounding of the xfmr create objectionable current?

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[Wire-Smith]

In future anyone can just place new 277V load on the panel without knowing. Also, the secondary of xfmr would have to be grounded 250.30, bonding neutral to gnd and GEC to bldg steel or water pipe ofcourse and need to comply per NEC 2014 Article 450.22 over 112.5kva. Would the grounding of the xfmr create objectionable current?

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Grounding the premises xfmr we are talking about will not create an opportunity for objectionable current.

They could put a warning label at the 480/277panelboards for objectionable current if any neutral loads are added to the service.

The premises xfmr grounding won't create objectionable current because there will only be one neutral to ground bond on the secondary. And the primary will have no neutral load.

 

[hhsting]

Grounding the premises xfmr we are talking about will not create an opportunity for objectionable current.

They could put a warning label at the 480/277panelboards for objectionable current if any neutral loads are added to the service.

The premises xfmr grounding won't create objectionable current because there will only be one neutral to ground bond on the secondary. And the primary will have no neutral load.

Well their is second xfmr dowmstream 480 to 208/120V three phase that will have neutral to bond at the transformer and GEC to bldg steel or underground water will not create objectionable current?

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[Wire-Smith]

Well theor is second xfmr dowmstream 480 to 208/120V three phase that will have neutral to bond at the transformer and GEC to bldg steel or underground water will not create objectionable current?

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Will not,

If there is only one neutral to ground connection on a system(isolation xfmr secondary) then there is no parallel path for the neutral current to divide upon

 

[hhsting]

Will not,

If there is only one neutral to ground connection on a system(isolation xfmr secondary) then there is no parallel path for the neutral current to divide upon

Great will just present both options see what they take.

On another separate note just for knowledge if you have one service and lets say that service feeds trough with four service disconnects all grouped in one location and all of them have neutral to ground bond, each disconnect has GEC to same common grounding electrodes then that scenario would not create objectionable current?

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[kwired]

Is it just one service though? I thought code states you can’t have 2 services for exception for special conditions?

Which a fire pump is one of those conditions.

Ok 230.72(B) fire pump service disconnect is allowed to be remote than normal service disco.

Sorry if someone addressed it already I have not read all the posts thoroughly, but read that section carefully, fire pump service disconnect is required to be remote from the normal service. That requirement is going to naturally introduce objectionable current paths in some situations. With good design practices there may be ways to minimize those paths, but if you have a lot of building steel or metallic piping chances are you won't totally eliminate them either.

 

[hhsting]

Which a fire pump is one of those conditions.



Sorry if someone addressed it already I have not read all the posts thoroughly, but read that section carefully, fire pump service disconnect is required to be remote from the normal service. That requirement is going to naturally introduce objectionable current paths in some situations. With good design practices there may be ways to minimize those paths, but if you have a lot of building steel or metallic piping chances are you won't totally eliminate them either.

Yes FP disco will be remote just convert 277V single phase load that cause neutral current to 120/208V after premise transformer bonded at one point and keep 480V three phase load.

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[Wire-Smith]

Great will just present both options see what they take.

On another separate note just for knowledge if you have one service and lets say that service feeds trough with four service disconnects all grouped in one location and all of them have neutral to ground bond, each disconnect has GEC to same common grounding electrodes then that scenario would not create objectionable current?

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Best to be bolted together and internal bonding(white wire)

Or Your GEC connecting them all will likely carry current, I would put danger labels if that's the case.

 

[hhsting]

Best to be bolted together and internal bonding(white wire)

Or Your GEC connecting them all will likely carry current, I would put danger labels if that's the case.

Nec 2014 Article 250.64(D)(2) does not mention bolting them together

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