Several Motors on One Branch Circuit Calculator
Check whether a group of motors can share one branch circuit under NEC Article 430, and size the single short-circuit and ground-fault device. The tool pulls each motor's full-load current from Table 430.250 or 430.248, sizes each branch device with Table 430.52, then evaluates the three 430.53 methods: the (A) small-motor allowance, the (B) smallest-motor device, and the (C) group-installation device.
How to use this calculator
- Set the circuit phase and voltage. Every motor on the shared circuit uses that same system.
- Choose the motor type and the branch device family. Table 430.52 sets each motor's device percentage.
- Add each motor by horsepower, with a quantity for identical motors. The tool reads full-load current from Table 430.250 (three-phase) or Table 430.248 (single-phase), not the nameplate.
- Add any non-motor load in amperes if the circuit also serves other loads.
- Read the maximum group device (430.53(C)), whether the small-motor allowance (430.53(A)) applies, and the smallest-motor device (430.53(B)).
NEC reference
This calculator follows NEC 2020 430.53 (Several Motors or Loads on One Branch Circuit). Full-load current is taken from Table 430.248 (single-phase) or Table 430.250 (three-phase) per 430.6(A)(1), and each motor's branch device from Table 430.52 with the 430.52(C)(1) next-higher-standard allowance. 430.53(A) permits several motors of 1 hp or less drawing 6 A or less on a 15 A or 20 A circuit; 430.53(B) sizes a single device to the smallest motor; 430.53(C) sizes a single group device to the highest-rated motor's device plus the other loads, taken as a maximum. These values are stable across the 2017, 2020, and 2023 editions, except that the 2020 edition raised the low-voltage threshold in 430.53(A) from 600 V to 1000 V.
Results are for reference only. Verify against the applicable adopted edition of the NEC and consult a licensed electrician for code compliance.
The three ways to share a branch circuit
A motor branch circuit normally serves one motor, because the short-circuit and ground-fault device has to ride through that motor's starting inrush without opening. NEC 430.53 is the exception that lets more than one motor, or one or more motors plus other loads, sit on a single branch circuit. It gives three separate paths, and the device rule is different for each.
- 430.53(A) Not Over 1 Horsepower. Several motors, each 1 hp or smaller and drawing 6 A or less, are permitted on a nominal 120V circuit at not over 20 A, or a circuit of 1000V or less at not over 15 A, with individual overload protection.
- 430.53(B) If Smallest Rated Motor Protected. A single device sized to the smallest motor, allowed only where it can be shown the device will not open under the most severe normal service.
- 430.53(C) Other Group Installations. A single device sized to the highest-rated motor's branch device plus the full-load currents of the other loads, with controllers and overload devices listed for group installation.
Worked example: 10, 15, and 25 HP at 460V
- Full-load currents from Table 430.250: 14 A, 21 A, and 34 A.
- The highest-rated motor is 25 HP. Its inverse-time breaker per Table 430.52 (250 percent, rounded up) is 34 x 2.5 = 85 A, rounded to 90 A.
- 430.53(C) ceiling: 90 A + the other motors 14 + 21 = 90 + 35 = 125 A.
- 125 A is a standard 240.6(A) rating, so the single group breaker is 125 A maximum.
- None of these motors is 1 hp or smaller, so the 430.53(A) small-motor allowance does not apply. Sized to the smallest motor, 430.53(B) would allow only 35 A.
Why the small-motor test reads the full-load current
The 430.53(A) allowance has two limits that both have to pass: 1 hp or smaller, and a full-load current of 6 A or less. Horsepower alone is not enough. A 1 hp motor at 115V single-phase draws 16 A from Table 430.248, so it clears the horsepower limit but fails the current limit and cannot use the small-motor allowance. Because the calculator reads each current from the table, it catches that case instead of trusting the nameplate horsepower.
Frequently asked questions
Can you put several motors on one branch circuit?
Yes, under NEC 430.53. Two or more motors, or motors plus other loads, may share a branch circuit under 430.53(A), (B), or (C), each with its own device rule, and each motor still needs individual overload protection under 430.32.
What is the 430.53(A) small-motor rule?
Several motors, each 1 hp or smaller and 6 A or less, may share a nominal 120V circuit at up to 20 A, or a circuit of 1000V or less at up to 15 A. The 2020 edition raised that voltage threshold from 600V to 1000V.
How is the 430.53(C) group device sized?
The single device is no larger than the highest-rated motor's 430.52 branch device plus the sum of the other motors' and loads' full-load currents. It is a maximum, so a non-standard result rounds down to the next 240.6(A) rating, and it requires group-listed equipment.
Does this size the wire too?
No. It sizes the shared device and the method only. The common conductor and the 430.53(D) tap to each motor are separate; use the Multi-Motor Feeder, Wire Ampacity, or Wire Size calculators for the conductor.
Related calculators
- Multi-Motor Feeder Calculator: the 430.24 conductor and 430.62(A) device for a feeder that supplies several motor branch circuits.
- Motor Breaker Sizing Calculator: the branch-circuit device and conductor for a single motor.
- Motor Overload Protection Calculator: the running-overload relay each motor needs under 430.32.
- Motor Full-Load Current Calculator: the Table 430.248/430.250 full-load current lookup.
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