Continuous = 3 h or more at full load. OCPD ≥ non-continuous + 1.25 × continuous · NEC 210.20(A)/215.3 · CEC 8-104.
NEC Table 430.250 / CEC Table 44 stop at 575 V - there is no standard FLC table for medium-voltage motors. Enter the motor's full-load current below (from the nameplate or manufacturer data).NEC Table 430.250 / CEC Table 44 are three-phase/single-phase AC tables - no FLC table exists for a DC motor at any voltage. Enter the motor's full-load current below (from the nameplate or manufacturer data).
Allow increase for hard starting430.52(C)(1) Ex.2 ceilings if motor won't start on the base setting
Supervised location (> 1000 V only)Qualified-persons access · Table 450.3(A)
NEC 690.8(A)(1)(a)(1)/690.9(B)(1): max circuit current = 125% × ΣIsc, then the OCPD ≥ 125% of THAT (both 125% steps apply). CEC 64-206(b): OCPD ≥ 125% × Isc, capped by 64-214(2) above.
NEC 706.30(A)(1): max current = nameplate rated current - use the GREATER of charge/discharge if they differ. NEC 706.31(B): OCPD ≥ 125% of that. CEC gives no percentage formula for ESS/battery OCPD sizing (Rule 64-806 requires a current-limiting OCPD where available battery short-circuit current exceeds equipment ratings, but sets no percentage) - this tool uses NEC's 125% as the closest defensible basis under CEC too, flagged explicitly below.
NEC 690.8(A)(1)(b): max circuit current = sum of parallel DC-to-DC converter continuous output current ratings. OCPD ≥ 125% of that (690.9(B)(1)).
3Conductor (Protection Check)
4Device & System Protection
Device type
Fuse
Circuit breakerBoth on compares fuse and breaker
Prefer time-delay / dual-elementRides motor & transformer inrush
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Disclaimer and reference standards
Engineering aid - verify before use. Results are not a stamped design.
The engineer of record is responsible for the final selection, and no warranty is expressed
or implied.
Standard ratings: NEC 240.6(A) / CEC Table 13.
Motor branch-circuit protection: NEC 430.52 / CEC Rule 28-200 and Table 29.
Transformer protection: NEC 450.3 / CEC Rules 26-250, 26-252 and 26-254.
Conductor protection: NEC 240.4, including the 240.4(D) small-conductor limits.
PV source/output circuits (DC): NEC 690.8(A)(1)(a)(1) and 690.9(B)(1) (max circuit
current = 125% × ΣIsc; OCPD ≥ 125% of that max current, rounded up per 240.4(B) - the two
125% steps compound) / CEC 64-206(a)-(b) and 64-214(2),(5) (OCPD ≥ 125% of rated
short-circuit current, but not more than the LESSER of the conductor ampacity or the module
nameplate maximum OCPD - a ceiling, not a floor - with the next higher standard rating
permitted where that value doesn't correspond to one).
DC-to-DC converter circuits: NEC 690.8(A)(1)(b) (max circuit current = sum of
parallel converter continuous output current ratings) and 690.9(B)(1) (OCPD ≥ 125% of that).
Energy storage systems / batteries (DC): NEC 706.30(A)(1) (max current = nameplate
rated current, or the greater of separate charge/discharge ratings) and 706.31(B) (OCPD ≥
125% of that) / CEC Rule 64-806 (a current-limiting OCPD is required in each battery circuit
where the battery's available short-circuit current exceeds the short-circuit rating of other
equipment in that circuit - CEC sets no percentage formula for this sizing; this tool uses
NEC's 125% as the closest defensible basis under CEC and flags it explicitly).
DC-rated devices: NEC 706.31(C) and CEC 64-058(3) require that OCPDs used in any DC
portion of an energy storage or renewable energy power system be listed/marked for DC use,
with the appropriate DC voltage, current and interrupting ratings - an AC-rated device is not
a substitute; DC has no current zero crossing to help the arc self-extinguish.
Device selection: the Authority Having Jurisdiction and the adopted edition of the
NEC/CEC govern. Confirm device ratings, interrupting capacity, voltage rating and
coordination against the manufacturer's published time-current curves, selectivity tables
and UL/CSA listings.