Fault Current: Available Fault Current, Interrupting Ratings, SCCR, Series Ratings and the 110.24 Label
"Fault Current" is its own bullet under *Services, Service Equipment & SDS* on the PSI outline. The knowledge items come almost entirely from 110.9, 110.10, 110.24, 240.83, 240.85, 240.86 and 230.95; the calculation items are the transformer "infinite bus" short-circuit calculation. Every number below was read from the 2026 text (viewer pages in the source pack) except the engineering formulas, which are standard practice and are marked as such.
NFPA 70 National Electrical Code, 2026 edition · Reviewed 2026-09-19
"Fault Current" is its own bullet under Services, Service Equipment & SDS on the PSI outline. The knowledge items come almost entirely from 110.9, 110.10, 110.24, 240.83, 240.85, 240.86 and 230.95; the calculation items are the transformer "infinite bus" short-circuit calculation. Every number below was read from the 2026 text (viewer pages in the source pack) except the engineering formulas, which are standard practice and are marked as such.
1. Three words the questions turn on
| Term | Where | What it means |
|---|---|---|
| Available fault current | Article 100 | The largest current capable of being delivered at a point on the system under a short-circuit condition (the utility and transformer set it; conductors reduce it). |
| Interrupting rating | Article 100 / 110.9 | The highest current at rated voltage that a device intended to interrupt current (fuse, circuit breaker) is identified to interrupt. Also called AIC/AIR. |
| Short-circuit current rating (SCCR) | Article 100 / 110.10 | The fault current that equipment not intended to interrupt (panelboards, MCCs, industrial control panels, disconnect switches, HVAC units) can withstand without extensive damage. |
110.9 — equipment intended to interrupt current at fault levels shall have an interrupting rating at nominal circuit voltage not less than the available fault current at its line terminals. Equipment intended to interrupt current at other than fault levels (a snap switch, a contactor) needs an interrupting rating for the current it must interrupt.
110.10 — the overcurrent devices, the total impedance, the equipment SCCR and other characteristics of the circuit shall be selected and coordinated so the protective devices clear a fault without extensive damage to the circuit's electrical equipment. Listed equipment applied within its listing is considered to comply.
Exam trap: a panelboard does not have an interrupting rating — it has an SCCR; the breakers inside it have interrupting ratings. A 10 kA-rated breaker in a 22 kA panelboard at a point with 18 kA available violates 110.9 (the breaker), no
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