120/240v single phase subpanel fed from 208y/120v three phase main breaker panel

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chris k baker

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I'm looking for suggestions on the best way to run a 60 amp 120/240 single phase subpanel from a 208y/120 three phase panel. Is a buck boost transformer needed, etc. Thanks for any help!
 
Are you looking for 240 volts that's why you need a transformer?

Welcome to the Forum. :)
 
LarryFine said:
Welcome to the forum.

For an automation system, I suggest a step-up, not a buck-boost.

I believe the line-to-neutral voltages will matter more.
Click to expand...

This.

Buck-boost transformers are ideal if you need straight 240V. But if you need 120/240V they are bad. When you use a normal buck-boost on a 208V system, one L-N voltage is 120V; the other leg ends up about 146V L-N.

If you fed a panel and could _guarantee_ that your 120V loads were on the 120V leg... (what is the likelihood that something gets changed 5 years down the road and a 120V device gets hit with 146V??)

If you want a 120/240V panel, use a step up transformer as @LarryFine suggests.

The other option worth considering is to feed the panel with 208V, and then use individual buck-boost transformers for the specific L-L loads which require 240V.

-Jonatahn
 
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