Ground-fault protection on large commercial services
Solidly grounded wye services over 150 V to ground and not over 1,000 V phase-to-phase, typically 480Y/277 V, need ground-fault protection of equipment on each service disconnect rated 1,000 A or more, tested when first installed.
What the code requires
Ground-fault protection of equipment (GFPE) is required on solidly grounded wye services of more than 150 V to ground but not over 1,000 V phase-to-phase, for each service disconnect rated 1,000 A or more. In practice that means 480Y/277 V services. A 208Y/120 V service does not trigger it, because it is not over 150 V to ground.
A disconnect's rating is the largest fuse that can be installed, or the highest continuous trip setting the breaker is rated for or can be adjusted to.
The protection must open all ungrounded conductors. The maximum setting is 1,200 A, with a maximum time delay of 1 second for ground-fault currents of 3,000 A or more. With a switch and fuses, the fuses must clear any current above the switch's interrupting capacity before the ground-fault protection opens the switch.
The system must be performance tested when first installed, by qualified persons using primary current injection per the equipment instructions, with a written record available to your inspector.
On the job
- No primary-injection test record at final inspection is a common holdup.
- Splitting a service into two to six smaller disconnects, each under 1,000 A, can avoid the requirement.
- The rule looks at the largest fuse that fits or the highest setting the breaker allows, not just the setting used.
Exceptions that matter
- Not required for a continuous industrial process where a nonorderly shutdown would add hazards.
Related sections
- NEC 215.10
- NEC 230.71: How many service disconnects are allowed
- NEC 240.13
- NEC 517.17
- NEC 695.6
Where this comes from
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Kyle Robert Anderson KBC Electric · CSLB #1073066 · C-10 Electrical · Licensed since 2021