bbaumer

Is there a "rule of thumb" for say building size for commercial or educational type occupancies where it probably makes sense to go to a 480/277V service instead of a 208/120V service?

Not looking for a detailed analysis just looking for a guideline that says "air conditioned office buildings greater than X square feet are worth it to go to 480/277V".

The thinking is the savings on copper, # breakers, number of lighting circuits, I2R losses, bus sizes etc. more than offset the cost of the dry transformer and higher voltage rating of equipment.

eg You probably would not feed a small 2,500 SF office building with 480V but you probably would a 50,000 SF building.

Anyone consider this before?

thanks,
bbaumer

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BryanMD

You've pretty well nailed the parameters of why to use 480,
and then step down as needed.

The only 'rules of thumb' I'm aware of is "is 480 available?".
If so, then do so... even on the smaller jobs.

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macmikeman

On small jobs the offset of the wire size for feeders may not pay for the cost of the step down transformer(s), and the higher rated distribution equipment.

480sparky

That's generally determined by the windings in the POCO transformer. If it's a new building, you may get your choice since the tranny's not set yet.

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JohnJ0906

Seems to me, this would usually be something an engineer would figure out working with the customer, as far as availability, cost considerations, exactly what equipment and lighting is desired.

In addition to the things others have mentioned, the equipment, lighting, and other loads are a consideration as well.

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randomkiller

Sometimes I think it's just a matter of what the design engineer is most familiar with and what he likes. We do some small places with 480 services, that have very large a/c loads because of the IT racks and need power.

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micromind

Around here, a 200 amp service of either voltage needs a simple meter-main. Anything larger, the POCO requires a switchgear with an underground pull section. They don't do overheads of more than 200 amps. The cost of switchgear can easily offset the cost of a transformer.

Rob