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Discussion of Delta 3ph services. Open, Closed, etc

Discussion of Delta 3ph services. Open, Closed, etc

Discussion of Delta 3ph services. Open, Closed, etc

(OP)
I cannot seem to get a straight answer from most electricians and I think this is mostly out of their scope of expertise and I am not an EE so hoping to get something from the horses mouth.  

When discussing Delta connections, some have indicated you may or may not have a high leg.  I have NEVER seen a Delta system without a high leg.  I am trying to gather some connection drawings of the different Deltas to better understand this.  Per my understanding, the open delta uses on 2 transformers and 2 legs of input power to triangulate the 3 phase but still creates a high leg to the neutral reference.  This load will largely be unbalanced so is only good for small installations.  Closed delta uses 3 cans.  I can see no way with either to eliminate the high leg while still offering A and B to neutral loading.  

Can someone clarify this is laymen terms for me...??

RE: Discussion of Delta 3ph services. Open, Closed, etc

Any delta with a center tap neutral will have a high leg.  Any delta with a corner ground will not have a high leg.  Any ungrounded delta will not have a high leg.

RE: Discussion of Delta 3ph services. Open, Closed, etc

(OP)
Would you have any drawings or references on the different connections?  I will assume the center tapped delta is most common in building installations where L-N loads are common and the corner ground delta might be used on dedicated installs like pumps?   

RE: Discussion of Delta 3ph services. Open, Closed, etc

Corner grounding is extremely rare, at least in the US.  The center-tapped (wild-leg) delta is used mostly for small pump installations where the predominant load is three-phase with a small amount of 120 V. load.  Both configurations are best avoided if possible.  The open-delta center-tapped approach is sometimes used where there is a small amount of three-phase load (small motors) and more single-phase load (or where only V-phase primary is available.  

When three-phase power is needed to a building, best options are 208/120V or 480/277V.  

 

David Castor
www.cvoes.com

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