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#91618 - 01/25/05 12:14 PM High Leg Practice  
Ragu  Offline
Junior Member
Joined: Jun 2001
Posts: 7
Elkton, Md USA
I have a delta-delta xmfr feeding a 240V panel. 2 phases to X4 (neutral) provide 120V, the 3rd phase, or Hi leg will not produce 120V to X4.

My question is around acceptable practice. Can the neutral (X4) be run to the panel and the 3rd phase marked as "Hi Leg do not use for 120V single phase". I've seen this done but I'm wondering
1-Is this a code violation?
2-Is this "good" practice? Or should 120V just not be fed from this panel. Don't run the neutral (X4) to the panel and therefore no mistake can be made?

Thanks


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#91619 - 01/25/05 01:36 PM Re: High Leg Practice  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,069
Estero,Fl,usa
110.15 High-Leg Marking.
On a 4-wire, delta-connected system where the midpoint of one phase winding is grounded to supply lighting and similar loads, the conductor or busbar having the higher phase voltage to ground shall be durably and permanently marked by an outer finish that is orange in color or by other effective means. Such identification shall be placed at each point on the system where a connection is made if the grounded conductor is also present.


Greg Fretwell

#91620 - 01/25/05 01:57 PM Re: High Leg Practice  
Anonymous
Unregistered

See also 408.3 (E) High leg on B phase.
See 250.24 (B) Grounded conductor required to be brought to service equipment.
See 250.20 (B) System required to be grounded.


#91621 - 01/25/05 07:59 PM Re: High Leg Practice  
Bjarney  Offline
Moderator
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
 
Buried on the IEEE C57.12 transformer standards are two variations for tapped-delta secondary terminal designations. If the highleg is across from grounded terminal X2, it is labeled X6. If the highleg is across from grounded terminal X3, it is labeled X4.

[Linked Image]

If 120V is needed {say for controls} it would be grounded to form a separately derived system, although not a “:neutral” for the unsymmetrical phase-to-ground voltages. If the corresponding delta-tap terminal is grounded, highleg marking is in order for your and others’ safety.


#91622 - 01/25/05 11:34 PM Re: High Leg Practice  
Nick  Offline
Member
Joined: Aug 2001
Posts: 599
Riverside, CA
All marking requirements aside, from a design stand point the most fool proof way is to not bring the high leg phase to your 120V panels. Feed three phase loads from separate 3 phase panels with no neutral taken to them. Feed 120V panels single phase + N. No high leg. I did a church once that was designed this way and it worked out well.



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