NEC Article 110.15 High-Leg Marking – Important points for Engineers

This article is about NEC Article 110.15 High-Leg Marking.

NEC Article 110.15 High-Leg Marking

If one phase winding of a 4-wire delta-connected system is grounded, the conductor or busbar with the higher voltage to ground should be clearly marked with an orange outer finish or other effective method at each connection point where the grounded conductor is present.

Electricians should test each phase of a 240/120-volt 3-phase, 4-wire delta system to determine where the high leg is located. The high leg should be clearly marked with the color orange or other similar effective means to prevent any problems due to the lack of standardization when both metered and nonmetered equipment are installed in the same installation.

Summary of NEC Article 110.15

1. On a 4-wire, delta-connected system with the midpoint of one phase winding grounded, the conductor or busbar with the higher phase voltage to ground needs to be durably and permanently marked by an outer finish that is orange in color or by other effective means.
2. This identification should be placed at each point on the system where a connection is made if the grounded conductor is also present.
3. The high leg is common on a 240/120-volt 3-phase, 4-wire delta system and is typically designated as “B phase.”
4. Electricians should always test each phase relative to ground with suitable equipment to determine exactly where the high leg is located in the system.