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Joined: Mar 2001
Posts: 2,056
Redsy Offline OP
Does this configuration have one transformer larger or smaller than the other two (due to the high-leg not being utilized for 120 volt loads)?

Joined: Oct 2000
Posts: 2,721
Broom Pusher and

The 4 Wire Delta has a center Pot, which is sized according to the expected 120 VAC 1Ø 2 Wire (or combined 120/240 VAC 1Ø 3 Wire loads).

Larger center Transformers where more 1Ø 120 VAC needed, smaller where less is needed.


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Joined: Mar 2001
Posts: 2,056
Redsy Offline OP
Thanks, Scott.
I thought I'd seen larger ones, then recently, I saw a smaller one. This explains it.

Joined: Apr 2002
Posts: 2,527
(…under construction…)

Truth is, four-wire delta banks can have any size transformers, including one “zero-size” pot—that being only two transformers—a/k/a an “open delta” bank. See IEEE std C57.105-1978 §6/§8 or odds’n’sods from EPE overhead standards linked at (~1MB) for some sizing guidelines (that are not necessarily NEC-based.) A ‘shorthand’ sketch of delta and open-delta secondary interconnection…

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[This message has been edited by Bjarney (edited 04-04-2005).]

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