Stepping up from 208/3 to 480/3?

[klubie]

We are in the process of having construction documents put together for a new 6,000 square foot Medical Office Building on our campus. We had planned on a 208V, 3-phase electrical service, however the x-ray machine we are planning to purchase is only available at 480V, 3-phase, wye distribution.

Is there a way for the electrician to provide a 208V, 3-phase service and then step up for that lone piece of equipment, or would it be more cost effective and make more sense to provide a 480V, 3-phase service, and then step down to 208V, 3-phase for the lower voltage requirements?

Please advise.

Thanks.
Klubie

 

[dpc]

I'd seriously consider a completely separate service for the X-ray machine and put it on its own transformer. X-ray machines can be a potent source of transients. I wouldn't recommend trying to step up the 208 V to 480 V. In theory it could be done, but you'd be setting yourself up for potential flicker problems and creating a blind alley for future expansion.

Most utilities limit the size of 208/120V systems so you'll want to check that. I tend to lean toward using 480 V if there is any question at all. It makes life a lot easier when that rooftop heat pump doubles in size during construction.

 

[klubie]

Should we consider trying to find a 208V, 3-phase x-ray machine?

 

[dpc]

They probably made it 480 V for a reason. You could ask, but that could actually make the transient problems even worse.

 

[jraef]

There are a lot of magnetics in X-ray machines and using a lower voltage will make those componentss bigger and heavier, which is likely another reason why they don't offer it.

You may want to check with your utility, they may be willing to provide you with a 2nd 480V drop very inexpensively.

JRaef.com
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[waross]

If you go for a dedicated service for the exray machine be sure to check the tarif carefully. With the intermitent nature of the load, you may incur ridiculous demand charges or punitive minimum billing.
Generally the system voltage is selected to match the greatest load.
If you are in Canada you may use 277/480 for most of your lighting circuits.
Another techique is to use 480 volts and install a dedicated dry type transformer near each lighting panel or group of panels. The saving in feeder costs helps defray the cost of the transformers.
And, if you have to you may use a step up transformer from 208 to 480. It may not be the best but many good designs are not perfect, but are compromises.
respectfully