Why not use the nameplate amps?

430.6(A)(1) requires the table values for conductor, switch and overcurrent sizing so that a replacement motor of the same horsepower fits the circuit. The nameplate current is used only for overload protection (430.32).

What breaker for a 10 hp 460 V motor?

FLC 14 A; inverse-time breaker up to 250 % = 35 A. A 35 A breaker is a standard size; if the motor will not start, 430.52(C)(1) Exception 2 allows up to 400 % for currents of 100 A or less.

The table has no 3 hp at 115 V single-phase; why?

Table 430.248 stops at 2 hp for 115 V (24 A); larger motors are not built for 115 V. The page prints “not listed” rather than a made-up figure.

Motor FLA calculator

Full-load current · Table 430.25014.0ATABLE VALUE10 hp, 460 V three-phase induction; use this table value, not the nameplate, for conductors and OCPD (430.6(A)(1)) · NEC 2017, identical to 2011

Phase

Horsepower

Voltage

Motor type (Table 430.52)

Branch-circuit conductors, minimum ampacity430.22: 125 % of the table FLC: 17.5 A
Inverse-time breaker, max 250 %Table 430.52; next standard size 35 A permitted by 430.52(C)(1) Ex. 1 where the value does not match a standard rating: 35.0 A
Dual-element time-delay fuse, max 175 %next standard 25 A: 24.5 A
Nontime-delay fuse, max 300 %: 42.0 A
Instantaneous-trip breaker, max 1100 %listed combination starters only: 154 A

Overload protection (430.32) uses the nameplate current, not the table; typically 115 % or 125 % by service factor and temperature rise. Multi-motor circuits, Design B exceptions and the 430.52(C)(1) exceptions are the electrician’s call.

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Motor branch circuits are sized from the NEC tables, not the nameplate: 430.6(A)(1) sends you to Table 430.248 for single-phase and 430.250 for three-phase motors. Pick the horsepower and voltage and read the full-load current, the conductor ampacity at 125 % (430.22), and the maximum overcurrent device by type from Table 430.52. Overload protection is the exception: it uses the nameplate (430.32).

Worked examples

10 hp three-phase at 460 V: Table 430.250: 14 A. Conductors 17.5 A (12 AWG at 75 °C carries 25 A). Inverse-time breaker up to 250 % = 35 A; dual-element fuse up to 175 % = 24.5 A, next standard 25 A. Open this run
1 hp single-phase at 115 V: Table 430.248: 16 A. Conductors 20 A (12 AWG); breaker up to 40 A, dual-element fuse up to 28 A, next standard 30 A. Open this run
25 hp three-phase at 208 V: 74.8 A. Conductors 93.5 A (3 AWG at 75 °C, 100 A); breaker up to 187 A, so a 175 A device, or 200 A by the 430.52(C)(1) Exception 1 next-size rule. Open this run
5 hp single-phase at 230 V: 28 A. Conductors 35 A (8 AWG at 75 °C, 50 A; 10 AWG is 35 A but 240.4(D) matters only for the OCPD); breaker up to 70 A. Open this run

How it is worked out

FLC is read from Table 430.248 (single-phase, 1/6 to 10 hp at 115, 200, 208, 230 V) or Table 430.250 (three-phase induction, ½ to 500 hp at 115 to 2300 V). Where the table prints a dash the page says so rather than interpolating.

Conductors: ampacity ≥ 1.25 × FLC (430.22). Branch-circuit short-circuit and ground-fault protection: ≤ FLC × the Table 430.52 percentage for the device type (nontime-delay fuse 300 %, dual-element fuse 175 %, instantaneous-trip breaker 800 % or 1100 % for Design B, inverse-time breaker 250 %), with the next standard size permitted by 430.52(C)(1) Exception 1 where the product is not a standard rating.

The figures behind it

NEC Tables 430.248 and 430.250: Full-load currents, 2017 text verbatim, cross-checked with the 2011 NECA-IBEW reproduction: identical. Synchronous-motor columns and the 90 / 80 % power-factor multipliers are in the data but not exposed in the picker. Source
NEC 430.22 and Table 430.52: 125 % conductor rule and the maximum OCPD percentages by motor and device type, 2017 text; standard ratings from 240.6(A). Source
Edition note: No open 2020 or 2023 copy was reachable; the 2011 and 2017 values match and “unchanged in 2023” is inferred. Source

Table 430.248: single-phase motor full-load current

Amperes, single-phase AC motors. The following values of full-load currents are for motors running at usual speeds and motors with normal torque characteristics. The voltages listed are rated motor voltages. The currents listed shall be permitted for system voltage ranges of 110 to 120 and 220 to 240 volts.

hp	115 V	200 V	208 V	230 V
1/6	4.4	2.5	2.4	2.2
1/4	5.8	3.3	3.2	2.9
1/3	7.2	4.1	4	3.6
1/2	9.8	5.6	5.4	4.9
3/4	13.8	7.9	7.6	6.9
1	16	9.2	8.8	8
1-1/2	20	11.5	11	10
2	24	13.8	13.2	12
3	34	19.6	18.7	17
5	56	32.2	30.8	28
7-1/2	80	46	44	40
10	100	57.5	55	50

Source: NEC 2017 (NFPA 70-2017) Tables 430.248, 430.250, 430.52; identical to 2011. Use these values, not the nameplate, for conductors, switches and short-circuit protection (430.6(A)(1)).

Table 430.250: three-phase motor full-load current

Amperes, induction-type squirrel cage and wound rotor, then synchronous at unity power factor. The following values of full-load currents are typical for motors running at speeds usual for belted motors and motors with normal torque characteristics. The voltages listed are rated motor voltages. The currents listed shall be permitted for system voltage ranges of 110 to 120, 220 to 240, 440 to 480, and 550 to 600 volts.

hp	115 V	200 V	208 V	230 V	460 V	575 V	2300 V	Sync. 230 V	Sync. 460 V	Sync. 575 V	Sync. 2300 V
1/2	4.4	2.5	2.4	2.2	1.1	0.9	—	—	—	—	—
3/4	6.4	3.7	3.5	3.2	1.6	1.3	—	—	—	—	—
1	8.4	4.8	4.6	4.2	2.1	1.7	—	—	—	—	—
1-1/2	12	6.9	6.6	6	3	2.4	—	—	—	—	—
2	13.6	7.8	7.5	6.8	3.4	2.7	—	—	—	—	—
3	—	11	10.6	9.6	4.8	3.9	—	—	—	—	—
5	—	17.5	16.7	15.2	7.6	6.1	—	—	—	—	—
7-1/2	—	25.3	24.2	22	11	9	—	—	—	—	—
10	—	32.2	30.8	28	14	11	—	—	—	—	—
15	—	48.3	46.2	42	21	17	—	—	—	—	—
20	—	62.1	59.4	54	27	22	—	—	—	—	—
25	—	78.2	74.8	68	34	27	—	53	26	21	—
30	—	92	88	80	40	32	—	63	32	26	—
40	—	120	114	104	52	41	—	83	41	33	—
50	—	150	143	130	65	52	—	104	52	42	—
60	—	177	169	154	77	62	16	123	61	49	12
75	—	221	211	192	96	77	20	155	78	62	15
100	—	285	273	248	124	99	26	202	101	81	20
125	—	359	343	312	156	125	31	253	126	101	25
150	—	414	396	360	180	144	37	302	151	121	30
200	—	552	528	480	240	192	49	400	201	161	40
250	—	—	—	—	302	242	60	—	—	—	—
300	—	—	—	—	361	289	72	—	—	—	—
350	—	—	—	—	414	336	83	—	—	—	—
400	—	—	—	—	477	382	95	—	—	—	—
450	—	—	—	—	515	412	103	—	—	—	—
500	—	—	—	—	590	472	118	—	—	—	—

For 90 and 80 percent power factor, the [synchronous] figures shall be multiplied by 1.1 and 1.25, respectively. A dash means the table lists no value. Source: NEC 2017 (NFPA 70-2017) Tables 430.248, 430.250, 430.52; identical to 2011.

Questions people ask

Why not use the nameplate amps?: 430.6(A)(1) requires the table values for conductor, switch and overcurrent sizing so that a replacement motor of the same horsepower fits the circuit. The nameplate current is used only for overload protection (430.32).
What breaker for a 10 hp 460 V motor?: FLC 14 A; inverse-time breaker up to 250 % = 35 A. A 35 A breaker is a standard size; if the motor will not start, 430.52(C)(1) Exception 2 allows up to 400 % for currents of 100 A or less.
The table has no 3 hp at 115 V single-phase; why?: Table 430.248 stops at 2 hp for 115 V (24 A); larger motors are not built for 115 V. The page prints “not listed” rather than a made-up figure.

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