480V service for single-tenant office, correct choice?

[LifeLongLearner]

Hi. I'm working on the design for a 19,000 SF, single-story, ground-up office building. It's for a single tenant, and there are no plans to have tenants. The HVAC is all electric, and I have to power a fire pump as well. There are also solar panels in the parking lot that I need to feed back through the meter. The calculated kVA is ~400kVA, which is a 500A, 480V service. Is there any reason to not go with 480V? If I did a 208V service, it would require a 1200A breaker.

 

[Knightryder12]

You would have to consider if you have enough room for step-down transformers in your electrical room or not. But other than that, no reason to not consider a 480V service.

 

[LifeLongLearner]

Thank you for the sanity check. I'm used to lighter commercial buildings, but this one feels like a tweener. Fortunately, the architect gave me a large mech/electrical room, so there's plenty of space for transformers.

 

[charlie b]

I would go with 480 myself. The floor is large enough to result in significant voltage drop in a 208V system from the electrical room to the edge of the floor. Will the architect give you a closet or two some distance from the main electrical room to put a transformer and a branch panel closer to the office loads?

 

[infinity]

The calculated kVA is ~400kVA, which is a 500A, 480V service. Is there any reason to not go with 480V?

Will the POCO actually provide 480 volts at only 400 kva?

 

[Knightryder12]

Will the POCO actually provide 480 volts at only 400 kva?

The utilities in FLA will do just about anything since the property owner now pays for all of the infrastructure to bring power to the building.

 

[Elect117]

I think 480V is generally a better option for empty buildings because it allows the occupancy to be more "industrial". I would go with 800A 480V personally. It also depends on the utility service planning guidelines but I would go largest switchgear before the maintenance switch and Arc Flash stuff kicks in.

For example, 277V lighting, 480V forklift chargers, motors, HVAC, etc. Typically smaller breakers and wire to do the same loads / motors.

The bigger cost comes in the form of kwh in large dry types. But that isn't necessarily the building owner's issue.

 

[infinity]

The utilities in FLA will do just about anything since the property owner now pays for all of the infrastructure to bring power to the building.

Right but there has to be a point where one system has less cost for the customer than the other system. I agree if money is no object go with 480 even if it ends up costing more upfront.

 

[AC\DC]

Right but there has to be a point where one system has less cost for the customer than the other system. I agree if money is no object go with 480 even if it ends up costing more upfront.

Does the power company really care what it cost a customer?

 

[infinity]

Does the power company really care what it cost a customer?

No but the customer may care if the designer comes up with a system that costs them more money then they need to spend.

 

[AC\DC]

No but the customer may care if the designer comes up with a system that costs them more money then they need to spend.

Oh yeah, I thought you were referring your statement to the power company

 

[LifeLongLearner]

I would go with 480 myself. The floor is large enough to result in significant voltage drop in a 208V system from the electrical room to the edge of the floor. Will the architect give you a closet or two some distance from the main electrical room to put a transformer and a branch panel closer to the office loads?

Yes, I think the architect would be accommodating to that, but the electrical room is rather centrally located. The furthest office is around 100' away.

 

[LifeLongLearner]

I think 480V is generally a better option for empty buildings because it allows the occupancy to be more "industrial". I would go with 800A 480V personally. It also depends on the utility service planning guidelines but I would go largest switchgear before the maintenance switch and Arc Flash stuff kicks in.

For example, 277V lighting, 480V forklift chargers, motors, HVAC, etc. Typically smaller breakers and wire to do the same loads / motors.

The bigger cost comes in the form of kwh in large dry types. But that isn't necessarily the building owner's issue.

I poorly phrased the title. I said tenant, but I should have said single occupant. The company occupying the building will own the building as well.

 

[don_resqcapt19]

With 480 volt service the transformer losses for the 480-208Y/120 transformer(s) will be paid by the building owner forever.

 

[Elect117]

I poorly phrased the title. I said tenant, but I should have said single occupant. The company occupying the building will own the building as well.

With 480 volt service the transformer losses for the 480-208Y/120 transformer(s) will be paid by the building owner forever.

It is a give and a take. You just need to balance that out. I think the introduction of 277V lighting helped sway it towards the 480V side but Don is 100% correct. You will pay for the load losses in the step down transformers. The upfront cost and space requirements might be less but long term your losses in kwh will catch up with utility billing.

Some commercial dry storage don't need more than a couple offices of receptacles so it is okay long term. They benefitted more from dock / forklift chargers being 480V.

But for an office building where everything is 120V recept. you might lose out on that benefit. At that point the only benefit is less voltage drop at 277 or 480V and HVAC.

 

[gadfly56]

With 480 volt service the transformer losses for the 480-208Y/120 transformer(s) will be paid by the building owner forever.

For a 19,000 square foot building, the fire pump may need to be 480V. The OP should check for any other mandatory loads and their voltage requirements.