Al, here is a graphic to accompany the others explanations.

A high leg is an unavoidable and unused voltage point to the grounded conductor on a Delta configuration of transformer windings.

[Linked Image]

Concerning NM in Commercial buildings

Quote
334.10 Uses Permitted

Type NM, Type NMC, and Type NMS cables shall be permitted to be used in the following:

(1) One- and two-family dwellings.

(2) Multifamily dwellings permitted to be of Types III, IV, and V construction except as prohibited in 334.12.

(3) Other structures permitted to be of Types III, IV, and V construction except as prohibited in 334.12. Cables shall be concealed within walls, floors, or ceilings that provide a thermal barrier of material that has at least a 15-minute finish rating as identified in listings of fire-rated assemblies.

(4)Cable trays in structures permitted to be Types III, IV, or V where the cables are identified for the use.

FPN: See 310.10 for temperature limitation
of conductors.

So yes, NM can be used in commercial buildings if the prohibitions covered in 334.12 are taken into consideration.

Roger



[This message has been edited by Roger (edited 04-24-2006).]