Figure 3-1. Ground-fault protection shall be provided with 277/480-V, three-phase, four-wire services

DOE-HDBK-1092-98

Utility

Service

equipment

1000 A or more OCPD

NEC 230-95

Shunt trip CB

0 to 1200 A setting

NEC 230-95 (a)

Clearing time

shall clear a fault

of 3000 A or more

Grounding

in 1 second

electrode

conductor

Ground fault sensor

To load

Z93 0403

NEC Section 230-95

Figure 3-1. Ground-fault protection shall be provided with 277/480-V, three-phase, four-wire services with

overcurrent protection devices of 1,000 A or more. A ground fault sensor (window) can be used to encircle

all service conductors, including the grounded conductor (neutral).

3-5