🌀How many amps does a motor draw?

✓ Tested & verified Updated: Aug 10, 2026 How we calculate this

Motor full-load current

Supply

Motor voltage

Motor size in horsepower

28 amps full load

for a 5 HP motor, from Table 430.248 rather than from the nameplate · conductors are sized for 35 A

Copper conductor at 125%: 8 AWG
Inverse-time breaker, ceiling 250%: 70 A (max 70)
Overload relay, 115–125% of nameplate: 32.2–35 A
Shaft rating in each unit: 3.73 kW · 5.07 metric HP (PS)

The table current is usually higher than the nameplate, and the code wants you to use the table.

A sizing aid from the published NEC tables, not a design — have it signed off by a licensed electrician against the code your inspector enforces. Calculations follow the US NEC; outside the US, follow your local electrical code.

Try also

How many amps does a motor draw?

The AmpSizer motor result for a 5 HP single-phase motor at 230 volts is 28 amps of full-load current, from NEC Table 430.248 — conductors sized for 35 A, which is 8 AWG copper, an inverse-time breaker up to 70 A, and an overload relay set between 32.2 and 35 A.

Three different multipliers on one circuit is what makes motors confusing. The conductor is 125% of the table current (430.22). The breaker may go to 250% (430.52), because it has to let the motor start. The overload relay is 115 to 125% of the nameplate (430.32), and it is the device that actually protects the motor.

So a breaker two or three times the conductor’s rating is not a mistake here. Overload protection and short-circuit protection are two separate jobs done by two separate devices.

Both code tables, with the conductor each motor needs at 125% of its table current, computed rather than retyped.

Single-phase motors, Table 430.248

Single-phase motors — NEC Table 430.248. These are the currents the code makes you size conductors and devices from, whatever the nameplate says (430.6(A)(1)).
Motor	115 V	208 V	230 V	Copper at 125 %, 230 V
1/6 HP	4.4 A	2.4 A	2.2 A	14 AWG
1/4 HP	5.8 A	3.2 A	2.9 A	14 AWG
1/3 HP	7.2 A	4 A	3.6 A	14 AWG
1/2 HP	9.8 A	5.4 A	4.9 A	14 AWG
3/4 HP	13.8 A	7.6 A	6.9 A	14 AWG
1 HP	16 A	8.8 A	8 A	14 AWG
1-1/2 HP	20 A	11 A	10 A	14 AWG
2 HP	24 A	13.2 A	12 A	14 AWG
3 HP	34 A	18.7 A	17 A	10 AWG
5 HP	56 A	30.8 A	28 A	8 AWG
7-1/2 HP	80 A	44 A	40 A	8 AWG
10 HP	100 A	55 A	50 A	6 AWG

Three-phase motors, Table 430.250

Three-phase squirrel-cage induction motors — NEC Table 430.250. These are the currents the code makes you size conductors and devices from, whatever the nameplate says (430.6(A)(1)).
Motor	208 V	230 V	460 V	Copper at 125 %, 230 V
1/2 HP	2.4 A	2.2 A	1.1 A	14 AWG
3/4 HP	3.5 A	3.2 A	1.6 A	14 AWG
1 HP	4.6 A	4.2 A	2.1 A	14 AWG
1-1/2 HP	6.6 A	6 A	3 A	14 AWG
2 HP	7.5 A	6.8 A	3.4 A	14 AWG
3 HP	10.6 A	9.6 A	4.8 A	14 AWG
5 HP	16.7 A	15.2 A	7.6 A	12 AWG
7-1/2 HP	24.2 A	22 A	11 A	10 AWG
10 HP	30.8 A	28 A	14 A	8 AWG
15 HP	46.2 A	42 A	21 A	6 AWG
20 HP	59.4 A	54 A	27 A	4 AWG
25 HP	74.8 A	68 A	34 A	4 AWG
30 HP	88 A	80 A	40 A	3 AWG
40 HP	114 A	104 A	52 A	1 AWG
50 HP	143 A	130 A	65 A	2/0 AWG
60 HP	169 A	154 A	77 A	3/0 AWG
75 HP	211 A	192 A	96 A	250 kcmil
100 HP	273 A	248 A	124 A	350 kcmil

Why three phase halves the wire

Compare the two tables at 5 HP: 28 amps single phase at 230 V, 15.2 amps three phase at the same voltage. Same work, 46% of the current, two conductor sizes smaller.

That is the practical reason workshop equipment is three phase wherever it is available, and the reason a rotary phase converter is a serious option for a single large machine in a single-phase building. The other reason is starting: a three-phase motor produces a rotating field from the supply itself and needs no capacitor, no centrifugal switch and no starting winding — which are the three parts that fail on single-phase motors.

Frequently asked questions

Do I use the nameplate amps or the table amps?

Table amps for conductors, switches and short-circuit protection — 430.6(A)(1) says so explicitly. Nameplate amps for the overload relay, per 430.32. The table figures are deliberately generous so that a circuit sized from them suits any motor of that rating, which is why the two numbers differ.

Why can a motor breaker be 250 percent of the wire rating?

Because the breaker is not protecting against overload — the overload relay does that. The breaker only has to clear a short circuit or a ground fault, and it has to be large enough not to trip on the inrush every time the motor starts. Splitting the two functions is the whole design of Article 430.

How do I convert horsepower to amps?

For code purposes you do not convert, you look up: Tables 430.248 and 430.250 give the current for each horsepower and voltage. If you want the arithmetic anyway, one horsepower is 746 watts of shaft output, and electrical input is that divided by efficiency and then by voltage and power factor — which is why the table exists.

What size wire for a 5 HP motor?

8 AWG copper for a 5 HP single-phase motor at 230 V: the table current is 28 A, conductors go at 125% which is 35 A, and 10 AWG is blocked by the 240.4(D) ceiling of 30 A. A 5 HP three-phase motor at 230 V is only 15.2 A and takes 12 AWG.

Is 5 HP the same as 5 PS on an imported motor?

No, and it is the unit trap of this whole subject. Mechanical horsepower — what a US nameplate means — is 745.7 W, so 5 HP is 3.73 kW. Metric horsepower, written PS or CV, is 735.5 W, so a 5 PS motor is 4.93 mechanical HP and 3.68 kW. The 1.4% usually disappears into the code table’s rounding, and at the boundary between two rows it does not. Switch this calculator to kilowatts and it shows both.

Does a VFD change the motor circuit sizing?

Yes, substantially. With a variable frequency drive the conductors to the drive are sized from the drive’s input rating rather than the motor table, the drive provides the overload function, and 430.122 governs. The inrush problem largely disappears, which is one of the reasons drives are fitted at all.

How we calculate this

Full-load current comes from NEC Table 430.248 for single-phase motors and Table 430.250 for three-phase squirrel-cage induction motors, which 430.6(A)(1) requires to be used in place of the nameplate current for sizing conductors, switches and short-circuit protection. Branch-circuit conductors are 125% of that current per 430.22. The inverse-time circuit breaker ceiling is 250% per Table 430.52, and the figure shown is the largest standard rating from 240.6(A) that does not exceed it — 430.52(C)(1) Exception No. 1 permits the next higher standard size where the calculated value falls between two ratings. The overload relay range is 115–125% of the nameplate current per 430.32(A)(1). Conductor selection then applies Table 310.16 ampacity and the small-conductor ceiling of 240.4(D) as elsewhere on this site.

Worked example

With Supply Single phase, Motor voltage 230 V, Motor size in horsepower 5 HP, this page works out 28 amps full load. for a 5 HP motor, from Table 430.248 rather than from the nameplate · conductors are sized for 35 A

Copper conductor at 125%8 AWG
Inverse-time breaker, ceiling 250%70 A (max 70 )
Overload relay, 115–125% of nameplate32.2 – 35 A
Shaft rating in each unit3.73 kW · 5.07 metric HP (PS)

Sources:

The three protective devices on a motor

Overload relay. Sized from the nameplate at 115–125%. Protects the motor from working too hard for too long. This is the one that trips when a fan seizes.

Inverse-time breaker or fuse. Up to 250% of the table current for a breaker. Protects the conductor and the installation from a short circuit, and lets the motor start.

Disconnecting means. Within sight of the motor, or lockable, per 430.102. Not a protective device but a requirement all the same, and the one most often missing on a retrofit.