NEC 2026 Article 430: Motor Current and Conductor Basis
Source Metadata
- Code book: NEC 2026
- Sections filed: 430.6, 430.22, 430.250
- Why this matters: establishes when motor branch-conductor and motor branch short-circuit/ground-fault sizing must use NEC table full-load current instead of entered/nameplate current, and sets the 125% single-motor conductor rule.
- Image reference supplied with source:
4a13659f-fabe-11ef-875f-000d3a112b1a
430.6 Conductor Ampacity and Motor Rating Determination.
The size of conductors supplying equipment covered by this article shall be selected from the ampacity tables in 310.15 or shall be calculated in accordance with 310.14(B). Where flexible cord is used, the size of the conductor shall be selected in accordance with 400.5. The required conductor ampacity and motor ratings shall be determined in accordance with 430.6(A), 430.6(B), 430.6(C), and 430.6(D).
(A) General Motor Applications.
For general motor applications, current ratings shall be determined based on 430.6(A)(1) and 430.6(A)(2).
(1) Table Values.
Other than for motors built for low speeds (less than 1200 RPM), high torques, canned pumps, or multispeed motors, the values given in Table 430.247, Table 430.248, Table 430.249, and Table 430.250 shall be used instead of the actual current rating marked on the motor nameplate to determine the following:
(1) Ampacity of conductors
(2) Current ratings of switches
(3) Current ratings of branch-circuit short-circuit and ground-fault protection
Where a motor is marked in amperes, but not horsepower, the horsepower rating shall be assumed to be that corresponding to the value given in Table 430.247, Table 430.248, Table 430.249, and Table 430.250, interpolated if necessary.
Exception No. 1: Multispeed motors shall be in accordance with 430.22(B) and 430.52. Exception No. 2: For equipment that employs a shaded-pole or permanent-split capacitor-type fan or blower motor that is marked with the motor type and the marking on the equipment nameplate is not less than the current marked on the fan or blower motor nameplate, the full-load current marked on the nameplate of the appliance shall be used to determine the ampacity of branch-circuit conductors in addition to the current ratings of the following: (1) Disconnecting means (2) Motor controllers (3) Short-circuit and ground-fault protective devices (4) Separate overload protective devices Exception No. 3: For a listed motor-operated appliance that is marked with both motor horsepower and full-load current, the motor full-load current marked on the nameplate of the appliance shall be used instead of the horsepower rating on the appliance nameplate to determine the ampacity of branch-circuit conductors in addition to the current ratings of the following: (1) Disconnecting means (2) Motor controllers (3) Short-circuit and ground-fault protective devices (4) Separate overload protective devices
(2) Nameplate Values.
The motor nameplate current ratings shall be used to determine the values for the following:
(1) Separate motor overload protection
(2) For motors built for low speeds (less than 1200 RPM), high torques, canned pumps, or multispeed motors, the following:
a. Ampacity of conductors
b. Current ratings of switches
c. Current ratings of branch-circuit short-circuit and ground-fault protection
(3) Large motors exceeding the values in Article 430 Part XIV shall use the nameplate current rating for conductor sizing.
430.22 Single Motor.
Conductors that supply a single motor used in a continuous duty application shall have an ampacity of not less than 125 percent of the motor full-load current rating, as determined by 430.6(A)(1), or not less than specified in 430.22(A) through 430.22(G).
The requirement that a conductor have an ampacity of at least 125 percent of the motor full-load current (FLC) rating is based on the need to provide for a sustained running current that is greater than the rated full-load current and for protection of the conductors by the motor overload protective device set above the motor full-load current rating. The branch-circuit short-circuit and ground-fault protective device can be a fuse or a circuit breaker and must be capable of carrying the starting current of the motor without opening the circuit. Motor circuit conductors with an ampacity of 125 percent of the motor FLC are reasonably protected by motor overload protective devices set to operate at nearly the same current as the ampacity of the conductors. Motor circuit conductors are permitted to be protected by Article 430 in accordance with 240.4(G).
In general, every motor must be provided with overload protective devices intended to protect the motor windings, motor-control apparatus, and motor branch-circuit conductors against excessive heating due to motor overloads and failure to start. Overload is defined as the operation of equipment in excess of the normal full-load rating, which, when it persists for a sufficient length of time, causes damage or dangerous overheating. Overload in a motor includes a stalled rotor but does not include fault currents due to short circuits or ground faults.
For maximum ratings of short-circuit and ground-fault protective devices, see Table 430.52(C)(1). For conditions under which providing automatic opening of a motor circuit due to an overload could be undesirable, see 430.44.
(A) Direct-Current (dc) Motor-Rectifier Supplied.
For dc motors operating from a rectified power supply, the conductor ampacity on the input of the rectifier shall not be less than 125 percent of the rated input current to the rectifier. For dc motors operating from a rectified single-phase power supply, the conductors between the field wiring output terminals of the rectifier and the motor shall have an ampacity of not less than the following percentages of the motor full-load current rating: (1) Where a rectifier bridge of the single-phase, half-wave type is used, 190 percent.
(2) Where a rectifier bridge of the single-phase, full-wave type is used, 150 percent.
(B) Multispeed Motor.
For a multispeed motor, the selection of branch-circuit conductors on the line side of the controller shall be based on the highest of the full-load current ratings shown on the motor nameplate. The ampacity of the branch-circuit conductors between the controller and the motor shall not be less than 125 percent of the current rating of the winding(s) that the conductors energize.
(C) Wye-Start, Delta-Run Motor.
For a wye-start, delta-run connected motor, the ampacity of the branch-circuit conductors on the line side of the controller shall not be less than 125 percent of the motor full-load current as determined by 430.6(A)(1). The ampacity of the conductors between the controller and the motor shall not be less than 72 percent of the motor full-load current rating as determined by 430.6(A)(1).
Informational Note: The individual motor circuit conductors of a wye-start, delta-run connected motor carry 58 percent of the rated load current. The multiplier of 72 percent is obtained by multiplying 58 percent by 1.25.
(D) Part-Winding Motor.
For a part-winding connected motor, the ampacity of the branch-circuit conductors on the line side of the controller shall not be less than 125 percent of the motor full-load current as determined by 430.6(A)(1). The ampacity of the conductors between the controller and the motor shall not be less than 62.5 percent of the motor full-load current rating as determined by 430.6(A)(1).
Informational Note: The multiplier of 62.5 percent is obtained by multiplying 50 percent by 1.25.
(E) Other Than Continuous Duty.
Conductors for a motor used in a short-time, intermittent, periodic, or varying duty application shall have an ampacity of not less than the percentage of the motor nameplate current rating shown in Table 430.22(E), unless the authority having jurisdiction grants special permission for conductors of lower ampacity.
Most motor applications are continuous duty. For motors that are not continuous duty, the motor nameplate currents, and Table 430.22(E) are used to determine the branch-circuit ampacity. Branch-circuit conductors for a motor with a rated horsepower used for 5-minute short-time duty service periods are permitted to be sized smaller than for the same motor with a 60-minute rating, due to the cooling intervals between operating periods. For example, a 5-minute rated motor will run for 5 minutes and then be off for 55 minutes.
See also the definitions of the terms continuous duty, intermittent duty, periodic duty, short-time duty, and varying duty in Article 100.
(F) Separate Terminal Enclosure.
The conductors between a stationary motor rated 1 hp or less and the separate terminal enclosure permitted in 430.245(B) shall be permitted to be smaller than 14 AWG but not smaller than 18 AWG, provided they have an ampacity as specified in 430.22.
(G) Conductors for Small Motors.
Conductors for small motors shall not be smaller than 14 AWG unless otherwise permitted in 430.22(G)(1) or 430.22(G)(2).
(1) 18 AWG Copper.
18 AWG individual copper conductors installed in a cabinet or enclosure, copper conductors that are part of a jacketed multiconductor cable assembly, or copper conductors in a flexible cord shall be permitted, under either of the following sets of conditions: (1) The circuit supplies a motor with a full-load current rating, as determined by 430.6(A)(1), of greater than 3.5 amperes, and less than or equal to 5 amperes, and all the following conditions are met: a. The circuit is protected in accordance with 430.52.
b. The circuit is provided with maximum Class 10 or Class 10A overload protection in accordance with 430.32.
c. Overcurrent protection is provided in accordance with 240.4(D)(1)(2).
(2) The circuit supplies a motor with a full-load current rating, as determined by 430.6(A)(1), of 3.5 amperes or less, and all the following conditions are met: a. The circuit is protected in accordance with 430.52.
b. The circuit is provided with maximum Class 20 overload protection in accordance with 430.32.
c. Overcurrent protection is provided in accordance with 240.4(D)(1)(2).
(2) 16 AWG Copper.
16 AWG individual copper conductors installed in a cabinet or enclosure, copper conductors that are part of a jacketed multiconductor cable assembly, or copper conductors in a flexible cord shall be permitted under either of the following sets of conditions: (1) The circuit supplies a motor with a full-load current rating, as determined by 430.6(A)(1), of greater than 5.5 amperes, and less than or equal to 8 amperes, and all the following conditions are met: a. The circuit is protected in accordance with 430.52.
b. The circuit is provided with maximum Class 10 or Class 10A overload protection in accordance with 430.32.
c. Overcurrent protection is provided in accordance with 240.4(D)(1)(2).
(2) The circuit supplies a motor with a full-load current rating, as determined by 430.6(A)(1), of 5.5 amperes or less, and all the following conditions are met: a. The circuit is protected in accordance with 430.52.
b. The circuit is provided with maximum Class 20 overload protection in accordance with 430.32.
c. Overcurrent protection is provided in accordance with 240.4(D)(1)(2).
(H) Design BE and CE Motors.
Conductors that supply a single Design BE or CE motor used in a continuous duty application shall have an ampacity of not less than 125 percent of the motor full-load current rating, as determined by 430.6(A)(1). Conductors that supply a single Design BE or CE motor used in an application other than continuous duty shall have an ampacity per 430.22(E).
The sizing of any thermoplastic insulated or thermoset insulated copper or aluminum conductors with a temperature rating of 90°C (194°F) or less supplying a single Design BE or CE motor shall additionally limit the temperature of the conductors to a value not exceeding the insulation damage temperature of the conductors when locked-rotor current equal to that in Table 430.251(C) for the corresponding motor horsepower and voltage rating is drawn for a time duration of 5 seconds with the conductors initially at their rated maximum operating temperature. The temperature is limited in this manner under any of the following conditions: (1) The motor rating is less than or equal to 2 horsepower or greater than or equal to 125 horsepower.
(2) The motor locked-rotor current is reduced relative to that associated with full voltage, across-the line starting by any of the following means:
a. The motor is started with an adjustable speed drive.
b. The motor is started with a reduced voltage motor controller.
c. Starting on wye connection and running on delta connection is utilized.
(3) The allowable current computed with the following formula is greater than or equal to the locked-rotor current in Table 430.251(C) for the corresponding motor horsepower and voltage rating: [430.22(H)]
code book image: 4a13659f-fabe-11ef-875f-000d3a112b1a where: I = allowable short-circuit current (amperes) A = conductor area in circular mils as determined per Chapter 9 Table 8 t = time duration of 5 seconds c = 0.0297 for copper conductors or 0.0125 for aluminum conductors T 1 = rated maximum operating temperature of the conductor (°C) T 2 = maximum short-circuit temperature of the conductor, 150°C for thermoplastic insulated conductors or 200°C for thermoset insulated conductors k = 234 for copper conductors or 228 for aluminum conductors Fc = conductor short circuit factor which has a numerical value found in Table 430.22(H).
Formula image supplied with source material in thread context; file only the image reference ID here unless a local asset is later added.
430.250 Three-Phase ac Motors.
Table 430.250 shall provide values of full-load currents typical for motors running at speeds usual for belted motors and motors with normal torque characteristics. The voltages listed shall be rated motor voltages. The currents listed shall be permitted for system voltage ranges of 110 volts to 120 volts, 220 volts to 240 volts, 440 volts to 480 volts, and 550 volts to 600 volts.
Implementation Impact
- Branch conductor auto-sizing should use 430.6(A)(1) table values first for general motor applications, then apply 430.22 where applicable.
- Branch motor short-circuit and ground-fault auto-sizing should use the same 430.6(A)(1) table basis.
- Separate overload protection remains a nameplate-current case per 430.6(A)(2).