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#129481 - 03/30/05 06:19 PM 3 phase(240/120) delta bank
Redsy Offline

Registered: 03/28/01
Posts: 2138
Loc: Bucks County PA
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)?

#129482 - 03/30/05 07:10 PM Re: 3 phase(240/120) delta bank
Scott35 Offline

Broom Pusher and

Registered: 10/19/00
Posts: 2724
Loc: Anaheim, CA. USA

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!

#129483 - 04/02/05 06:19 PM Re: 3 phase(240/120) delta bank
Redsy Offline

Registered: 03/28/01
Posts: 2138
Loc: Bucks County PA
Thanks, Scott.
I thought I'd seen larger ones, then recently, I saw a smaller one. This explains it.

#129484 - 04/04/05 01:05 AM Re: 3 phase(240/120) delta bank
Bjarney Offline

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
(…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…


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


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