Transformer and CB sizing

P

Pflat

Member
Location
California
Occupation
Greenhouse horticulturist
Have a Project we are sourcing a transformer for.

We have a 208/120v 200amp 3phase panel to work from for primary.

We are trying to run 15 dehumidifier appliances that are 277v and draw 9amps each. Dehums will start at most 3 at same time, but will often all be running at same time. All 15 appliances on their own circuits, so 5 per phase equally balanced.

Electrician suggested a 480/277 panel (that we have already on site available to use) for secondary distribution to the dehumidifier appliance circuits, and a transformer between the 208/120 feed panel (primary) and the 480panel (secondary).. panel and transformer will only ever be used for these dehumidifier appliances, no other equipment will be added.

Can you recommend a transformer for this application, and availability? And breaker size on the 208 panel to feed primary?

Thank you
 
You need a step-up transformer with a 208V delta primary (ignore the 120V neutral) and a 480Y/277 secondary.
How big is the main breaker in the panel you are using?
 
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The subpanel we have available to draw from is 200 amps 3phase 208/120v, with some other circuits on it. If not possible off this panel to run 15, we would consider running less.

Amperage is off data plate. I am thinking I should connect one to a generator I have that will run 277 and measure it.

The help is very much appreciated
 
If the 9 amps is data plate, then I would go with a 30 KVA because they will draw less than that and probably there's an extra 25% built in anyway. A 30 KVA has a primary current of 83 amps. What kind of panel is the 208 panel? I would just try a 100 amp breaker. It may trip on startup from inrush now and then, and if that bothers you I would probably use a subfeed lug kit (or feed through lugs) to a 100A disconnect with RK5 fuses. For the 45 KVA, it would depend on what kind of panel you have. If you have a simple stab on panel I think your options will be limited to get over 100 amp sub feed option. You may have to just tap the mains.
 
30kVA would be fine for running them all. But hopefully there is a control system involved that will stagger start these after a power failure, otherwise you will need a much larger transformer to restart all of those at the same time, and that may run you into problems with the size of the 208V circuit for it.
 
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