Q. Where should the high-leg conductor from a 120/240V, 3-phase, 4-wire delta-connected system be landed? My utility requires it to be in the right hand or “C” phase position at the meter.



A. The NEC requirements are as follows:

Panelboards. Since 1975, panelboards supplied by a 3-phase, 4-wire delta-connected system must have the high-leg conductor (208V) terminate to the “B” (center) phase of a panelboard [408.3(E)] (Fig.1 at right).

An exception to 408.3(E) permits the high-leg conductor to terminate to the “C” phase when the meter is located in the same section of a switchboard or panelboard.

Disconnects. The NEC doesn't specify the termination location for the high-leg conductor in switch equipment (Switches — Art. 404), but the generally accepted practice is to terminate this conductor to the “B” phase.

Warning: When replacing equipment in existing facilities that contain a high-leg conductor, care must be taken to ensure that the high-leg conductor is replaced in the original location. Prior to 1975, the high-leg conductor was required to terminate on the “C” phase. Failure to re-terminate the high-leg in accordance with the existing installation can result in 120V circuits inadvertently connected to the 208V high-leg, which can have disastrous results.

Identification. On a 3-phase, 4-wire delta-connected system, where the midpoint of one phase winding is grounded, the conductor with the higher phase voltage-to-ground (208V) must be durably and permanently marked by an orange outer finish or another effective means. Such identification must be placed at each point on the system where a connection is made if the grounded neutral conductor is present (110.15, 215.8, and 230.56) (Fig. 2 above).

The high-leg conductor is also called the wild-leg, stinger-leg, or bastard-leg.

Utility equipment: As I understand it, the ANSI standard for meter equipment requires the high-leg conductor (208V-to-neutral) to terminate on the “C” (right) phase of the meter enclosure. This is because the demand meter needs 120V, which it gets from the “B” phase.