How Many Amps Does a 15 HP single-phase Motor Draw at 120V?

A 15 HP single-phase motor at 120V draws approximately 129.07 amps during normal operation (85% efficiency, PF 0.85). This HP and voltage combination is outside NEC Table 430.248, so there is no code-authoritative LRA multiplier for branch-circuit sizing; refer to the motor nameplate for both running current and startup characteristics.

15 HP single-phase motor at 120V

129.07 Amps running

Calculated running current at the motor terminals at the assumed 85% efficiency and PF 0.85. This is a conversion from the nameplate horsepower using those assumptions, not a measured value; a real meter reading depends on the motor's actual nameplate efficiency, loading, temperature, and motor design.

NEC Table 430.248 FLCoff-table (see nameplate)

Electrical input (HP × 746 ÷ efficiency)13,164.71 W

Try: 15HP at 120V 10HP at 120V 20HP at 120V 7.5HP at 120V

Volts

Motor Type

Running Amps (meter)

129.07

NEC Table 430.248 FLC (code sizing)

off-table

Use the running amps for metering and energy calculations. For branch-circuit sizing, AC motors use the NEC Table 430.248 / 430.250 full-load current under NEC 430.6(A)(1); DC motors use the motor nameplate full-load current under NEC 430.6(A)(3), with Table 430.247 as the reference. Three-phase current is shown per line on a balanced circuit.

Formula (single-phase)

I_(A) = (HP × 746) ÷ (V × Eff × PF)

(15 × 746) ÷ (120 × 0.85 × 0.85) = 11,190 ÷ 86.7 = 129.07 A

Convert HP to watts: 15 × 746 = 11,190W
Denominator: 120 × 0.85 × 0.85 = 86.7
Result: 11,190 ÷ 86.7 = 129.07 amps

NEC Reference Values

This section lists the Code reference numbers a motor branch circuit is sized from. Final conductor, breaker, disconnect, and overload selection is an install decision a licensed electrician makes against the motor nameplate, the actual install conditions, and the applicable NEC articles, not a decision a conversion page can make for you.

Off-Table: No Code-Anchored Sizing

This combination is off-table because 15 HP is not a listed horsepower rating in NEC Table 430.248. The table lists discrete HP values (for three-phase: 1/2, 3/4, 1, 1½, 2, 3, 5, 7½, 10, 15, 20, 25, 30, 40, 50, 60, 75, 100, and on up), and 15 HP falls between listed values. 120V itself is a standard single-phase voltage in the table.

Per NEC 430.6(A)(1) Exception, when a motor rating falls between listed HP values, the next higher listed HP is used for sizing.

Because there is no table FLC to anchor the NEC 430.22 conductor and 430.52(C)(1) OCP math, this page deliberately does not show branch-circuit sizing values for this variant. Multiplying the 129.07 A calculated running current by 125% or 250% would produce numbers that look authoritative but are not what the code requires.

What to do instead:

Pull the motor nameplate FLC and have a licensed electrician apply the 430.22 (conductor) and 430.52(C)(1) (OCP) rules against that number. NEC 430.6(A)(1) Exception permits using the next-higher listed HP where the motor rating is between table values; your inspector may also accept nameplate-based sizing for unusual HP ratings.

Operating Cost

Motor mechanical output is 11,190 W (15 HP × 746). Electrical input at the terminals is higher because no motor is 100% efficient: 11,190 ÷ 0.85 = 13,164.71 W. At $0.17/kWh, running cost is $2.24/hour or $537.12/month at 8 hours/day. Full breakdown at 13,164.71 W.

Amps by Motor Efficiency (single-phase)

Motor efficiency directly affects amp draw. A more efficient motor draws less current for the same HP output. Values below are the calculated single-phase running current at 120V and PF 0.85:

Efficiency	Amps at 120V	Watts Consumed	Waste Heat
75%	146.27 A	14,920 W	3,730 W
80%	137.13 A	13,987.5 W	2,797.5 W
85%	129.07 A	13,164.71 W	1,974.71 W
90%	121.9 A	12,433.33 W	1,243.33 W
95%	115.48 A	11,778.95 W	588.95 W

Other HP Values at 120V (single-phase)

Running current is the calculated single-phase draw at 85% efficiency and 0.85 PF (a conversion from HP under those assumptions, not a measured value). NEC Table FLC is the value from NEC Table 430.248 used for branch-circuit conductor and OCP sizing under NEC 430.6(A)(1). LRA is estimated at 5-7× the NEC table FLC; rows outside the table show n/a because there is no code-authoritative LRA basis for that HP/voltage/phase combination. Row links open each result page in single-phase mode.

HP	Running Amps (calculated)	NEC Table 430.248 FLC	LRA Estimate (5-7× FLC)
1/8 HP	1.08 A	off-table	n/a
1/6 HP	1.43 A	4.4 A	22-30.8 A
1/4 HP	2.15 A	5.8 A	29-40.6 A
1/3 HP	2.87 A	7.2 A	36-50.4 A
1/2 HP	4.3 A	9.8 A	49-68.6 A
3/4 HP	6.45 A	13.8 A	69-96.6 A
1 HP	8.6 A	16 A	80-112 A
1.5 HP	12.91 A	20 A	100-140 A
2 HP	17.21 A	24 A	120-168 A
3 HP	25.81 A	34 A	170-238 A
5 HP	43.02 A	56 A	280-392 A
7.5 HP	64.53 A	80 A	400-560 A
10 HP	86.04 A	100 A	500-700 A
15 HP	129.07 A	off-table	n/a
20 HP	172.09 A	off-table	n/a
25 HP	215.11 A	off-table	n/a
30 HP	258.13 A	off-table	n/a
40 HP	344.18 A	off-table	n/a
50 HP	430.22 A	off-table	n/a
75 HP	645.33 A	off-table	n/a

Same HP, Other Voltages (single-phase)

speed 15 HP at 208V = 74.46A speed 15 HP at 220V = 70.4A speed 15 HP at 230V = 67.34A speed 15 HP at 240V = 64.53A speed 15 HP at 400V = 38.72A speed 15 HP at 480V = 32.27A

Related Calculations

bolt 13,165W electrical input to amps at 120V payments 13,165W running cost

Frequently Asked Questions

How many amps does a 15 HP single-phase motor draw at 120V?expand_more

At the terminals, a 15 HP single-phase motor at 120V draws about 129.07 amps at 85% efficiency and 0.85 power factor. This specific HP and voltage combination is outside NEC Table 430.248, so NEC branch-circuit sizing must come from the motor nameplate and a licensed electrician, not from the calculated value above.

What is locked rotor amps for a 15 HP single-phase motor?expand_more

Locked-rotor startup current is typically 5-7 times the NEC table full-load current. Because this HP/voltage combination is not listed in NEC Table 430.248, there is no code-authoritative starting number for the multiplier; refer to the motor nameplate NEMA code letter for the actual LRA value.

What branch-circuit context does a 15 HP single-phase motor at 120V typically sit in?expand_more

At 120V single-phase, this is in US residential-receptacle territory (NEMA 5-15 or 5-20), but motor branch circuits are not general-purpose outlets. Motor conductors and OCP are sized per NEC 430.22 and 430.52(C)(1) against the NEC Table 430.248 FLC, with the 240.4(G) exemption from the small-conductor rule. Whether this specific motor sits on a shared receptacle, a dedicated 15/20A circuit, or a motor-rated disconnect is an install decision your electrician makes from the nameplate, startup current, and duty cycle, not from a calculated amp figure.

How does NEC 430.22 size conductors for a 15 HP single-phase motor?expand_more

NEC 430.22 sizes branch-circuit conductors at 125% of the table full-load current, but this HP/voltage combination is not listed in NEC Table 430.248. The correct input for the 430.22 formula here is the motor nameplate FLC, applied by a licensed electrician.

What is power factor for motors?expand_more

Motors typically run at PF 0.80-0.85 at full load. At no load, PF drops to 0.30-0.40. Low PF means the wire and breaker carry extra reactive current that does no useful mechanical work, which is why NEC motor sizing uses table FLC (which already accounts for typical PF) rather than a simple watts/volts calculation.

This calculator provides estimates for reference purposes only. Always consult a licensed electrician and verify compliance with the National Electrical Code (NEC) and local electrical codes before performing any electrical work.