Available fault current label at commercial services
Service equipment at other than dwelling units, such as commercial buildings, must be field-marked with the available fault current and the date it was calculated, and the marking must be updated when a change alters that value.
What the code requires
110.24(A): At other than dwelling units, service equipment must carry a legible field marking that shows the available fault current. The marking must include the date the fault-current calculation was performed and be durable enough for the environment.
The calculation itself must be documented, and the people authorized to design, install, inspect, maintain or operate the system must be able to get it.
110.24(B): When a modification to the electrical system changes the available fault current at the service, the value must be verified or recalculated, and the field marking must be updated to match.
On the job
- A commercial service with no fault-current label, or with a label that lacks the calculation date, does not meet this rule.
- The serving utility usually supplies the fault-current figure. Keep the calculation on file, because it must be available to the inspector.
Exceptions that matter
- Industrial installations are exempt from the markings when their maintenance and supervision ensure the equipment is serviced only by qualified persons.
Related sections
- NEC 110.9
- NEC 110.10
- NEC 110.16: Arc-flash warning labels on commercial equipment
- NEC 110.21(B): Requirements for field-applied warning labels
- NEC 230.82
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CSLB #354550 · C-10 Electrical · Licensed since 1978 · $25,000 contractor's bond