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10.6 Motors Part I: Full-Load Current, Conductors and Overload Protection

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Alaska Journeyman Electrician Study Guide Exam

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1 Chapter 1: Alaska Certificates of Fitness, Law & Exam Logistics

1.1 The Alaska Certificate of Fitness System 1.2 Journeyman Eligibility: 8,000 Hours and How Alaska Counts Them 1.3 Trainee, Residential Wireman, Lineman, Provisional & Reciprocal Certificates 1.4 The Journeyman Examination: Format, Scheduling, Open-Book Rules & Retakes 1.5 Adopted Codes, Fees, Renewal, Inspection & Enforcement

2 Chapter 2: Using the 2020 NEC

2.1 Article 90: Purpose, Scope, Arrangement & Enforcement 2.2 Navigating the Code Book: Structure, Index & Tabbing Strategy 2.3 Article 100 Definitions You Must Know Cold 2.4 Electrical Theory for the Exam: Ohm's Law, Power & Three-Phase

3 Chapter 3: General Requirements — Article 110

3.1 Approval, Listing, Interrupting Rating & Terminations 3.2 Temperature Limitations of Terminations — 110.14(C) 3.3 Working Space, Access, Egress & Illumination — 110.26(A) through (D) 3.4 Dedicated Equipment Space, Guarding & Over-1000-Volt Installations

4 Chapter 4: Conductors and Ampacity — Article 310

4.1 Conductor Types, Insulation Markings & Table 310.16 4.2 Ambient Temperature Correction and Alaska's Cold 4.3 Adjustment for More Than Three Current-Carrying Conductors 4.4 Putting It Together: Full Conductor-Sizing Problems 4.5 Parallel Conductors, Dwelling Service Sizing & Conditions of Use

5 Chapter 5: Wiring Methods and Materials — NEC Chapter 3

5.1 Article 300 General Requirements and Underground Cover 5.2 Thermal Movement: Expansion Fittings and Table 352.44 5.3 Boxes and Enclosures: Box Fill and Pull Box Sizing 5.4 Cable Assemblies: NM, MC, AC, SE, UF and TC 5.5 Raceways: RMC, IMC, EMT, FMC, LFMC, PVC and ENT 5.6 Conduit Fill: Chapter 9 Tables and Annex C 5.7 Cable Trays, Wireways, Busways, Gutters and Surface Raceways

6 Chapter 6: Branch Circuits and Feeders

6.1 Branch-Circuit Ratings, Conductor Sizing & Multiwire Circuits 6.2 Required Outlets and Receptacle Spacing in Dwellings 6.3 GFCI Protection — Article 210.8 6.4 AFCI Protection and Receptacle Requirements 6.5 Feeders and Outside Branch Circuits — Articles 215 and 225 6.6 Grounded Conductor Identification, Switches & Panelboards

7 Chapter 7: Overcurrent Protection — Articles 240 and 242

7.1 Article 240 Fundamentals: Ratings, Locations & Conductor Protection 7.2 Feeder Tap Rules — 240.21(B) 7.3 Transformer Secondary Conductors — 240.21(C) 7.4 Fuses, Circuit Breakers, Series Ratings & Article 242 Surge Protection

8 Chapter 8: Services and Load Calculations

8.1 Service Conductors, Clearances and Service Equipment 8.2 Service Disconnects, the 2020 Rule Change, SPDs and Service GFPE 8.3 Article 220 Part II: General Lighting, Receptacles and Demand Factors 8.4 The Standard Dwelling Calculation — Article 220 Part III 8.5 Optional Dwelling and Multifamily Calculations 8.6 Commercial and Industrial Load Calculations 8.7 Neutral Load Calculations and Harmonics — 220.61

9 Chapter 9: Grounding and Bonding — Article 250

9.1 System Grounding, 250.24 and the Main Bonding Jumper 9.2 The Grounding Electrode System — 250.50 through 250.53 9.3 Grounding Electrode Conductor Sizing and Installation 9.4 Bonding: Services, Metal Piping, Structural Metal and Other Systems 9.5 Equipment Grounding Conductors: Types, Sizing and Continuity 9.6 Separately Derived Systems and Separate Buildings 9.7 Ground-Fault Protection of Equipment and Grounding of Specific Equipment

10 Chapter 10: Equipment for General Use — NEC Chapter 4

10.1 Flexible Cords, Cables and Fixture Wires 10.2 Switches, Receptacles and Industrial Control Panels 10.3 Luminaires, Lampholders and Recessed Installations 10.4 Appliances and Fixed Electric Space Heating 10.5 Deicing, Snow Melting, Pipeline and Vessel Heating 10.6 Motors Part I: Full-Load Current, Conductors and Overload Protection 10.7 Motors Part II: Short-Circuit Protection, Controllers, Disconnects and HVAC

11 Chapter 11: Transformers, Generators and Special Occupancies

11.1 Transformers — Article 450 11.2 Generators, Storage Batteries and Energy Storage Systems 11.3 Hazardous (Classified) Locations — Articles 500 through 506 11.4 Garages, Hangars, Fuel Dispensing, Bulk Storage and Spray Application 11.5 Health Care Facilities — Article 517 11.6 Agricultural Buildings, Manufactured Homes, RV Parks and Marinas 11.7 Assembly, Theaters, Carnivals, Temporary Installations and Pools

12 Chapter 12: Special Equipment, Special Conditions and Exam Strategy

12.1 Signs, Cranes, Elevators, Electric Vehicle Charging and Welders 12.2 Solar Photovoltaic, Interconnection and Stand-Alone Systems 12.3 Wind Electric Systems and Fire Pumps 12.4 Emergency, Legally Required Standby, Optional Standby and COPS 12.5 Class 1, 2 and 3 Circuits, Fire Alarm, Optical Fiber and Communications 12.6 Cold-Climate Practice in Alaska: Code Basis and Engineering Judgment 12.7 Exam-Day Strategy: Navigation, Calculation Workflow and Time Management

10.6 Motors Part I: Full-Load Current, Conductors and Overload Protection

Key Takeaways Explain This Topic AI

NEC 430.6(A)(1) requires motor branch-circuit conductor sizing and short-circuit ground-fault protection to be based on the full-load current values in Tables 430.247 through 430.250, not the motor nameplate current.

NEC 430.22 requires branch-circuit conductors supplying a single continuous-duty motor to have an ampacity of not less than 125 percent of the motor's full-load current rating from the tables.

NEC 430.24 requires conductors supplying several motors to be sized at 125 percent of the highest rated motor plus the sum of the full-load currents of the other motors plus other loads.

NEC 430.32(A)(1) sizes separate overload protection for a continuous-duty motor over 1 horsepower using the motor nameplate full-load amperes: 125 percent for a service factor of 1.15 or greater or a temperature rise of 40 degrees C or less, and 115 percent otherwise.

NEC 430.6(A)(2) requires separate motor overload protection to be based on the motor nameplate current rating, which is the one place in Article 430 where nameplate rather than table values are used.

Last updated: August 2026

The Rule That Organizes Article 430

Motor circuits use two different current values, and knowing which one applies where is most of the battle:

  • Purpose Current to use Section
  • Conductor sizing Table FLC from 430.247–430.250 430.6(A)(1)
  • Branch-circuit short-circuit and ground-fault protection Table FLC 430.6(A)(1)
  • Motor disconnect ampere rating Table FLC 430.6(A)(1), 430.110
  • Overload protection Nameplate FLA 430.6(A)(2)

The reason is design intent. The tables give conservative, standardized values so that conductors and short-circuit protection are sized generously and consistently. Overload protection is meant to track the actual motor, so it uses the actual nameplate.

430.6(A)(1) Table Values. Other than for motors built for low speeds or high torque, and for multispeed motors, the values given in Tables 430.247, 430.248, 430.249, and 430.250 shall be used to determine the ampacity of conductors or ampere ratings of switches, branch-circuit short-circuit and ground-fault protection, instead of the actual current rating marked on the motor nameplate. Exception No. 1 applies to multispeed motors; Exception No. 2 to listed motor-operated appliances; Exception No. 3 to torque motors.

430.6(A)(2) Nameplate Values. Separate motor overload protection shall be based on the motor nameplate current rating .

430.6(B) Torque Motors. For torque motors, the rated current shall be locked-rotor current, and this nameplate current shall be used to determine the ampacity of the branch-circuit conductors, the ampere rating of motor overload protection, and the ampere rating of motor branch-circuit short-circuit and ground-fault protection.

430.6(D) Ampacity and Motor Rating Determination — Wye-Start, Delta-Run. For a wye-start delta-run connected motor, the selection of branch-circuit conductors on the line side of the controller shall be based on the motor full-load current, and the conductors between the controller and the motor shall be permitted to be sized at 72 percent of the motor full-load current rating.

The Tables

  • Table Covers
  • 430.247 DC motors
  • 430.248 Single-phase AC motors
  • 430.249 Two-phase AC motors (four-wire)
  • 430.250 Three-phase AC motors

Selected values from Table 430.250 , three-phase, full-load current in amperes:

  • Horsepower 208 V 230 V 460 V
  • 1 4.6 4.2 2.1
  • 2 7.5 6.8 3.4
  • 3 10.6 9.6 4.8
  • 5 16.7 15.2 7.6
  • 7.5 24.2 22 11
  • 10 30.8 28 14
  • 15 46.2 42 21
  • 20 59.4 54 27
  • 25 74.8 68 34
  • 30 88 80 40
  • 40 114 104 52
  • 50 143 130 65
  • 75 211 192 96
  • 100 273 248 124

Selected values from Table 430.248 , single-phase:

  • Horsepower 115 V 230 V
  • 1/2 9.8 4.9
  • 3/4 13.8 6.9
  • 1 16 8
  • 1.5 20 10
  • 2 24 12
  • 3 34 17
  • 5 56 28
  • Conductor Sizing — Part II

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 (G).

(A) Direct-Current Motor-Rectifier Supplied. For DC motors operating from a rectified power supply, specific multipliers apply.

(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.

(E) Duty-Cycle Service. 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) .

(G) Conductors for Small Motors. Conductors for small motors shall not be smaller than 14 AWG, with exceptions permitting 18 AWG and 16 AWG under stated conditions.

430.24 Several Motors or a Motor(s) and Other Load(s). Conductors supplying several motors, or a motor and other loads, shall have an ampacity not less than the sum of each of the following:

  • 125 percent of the full-load current rating of the highest rated motor , as determined by 430.6(A);
  • Sum of the full-load current ratings of all the other motors in the group, as determined by 430.6(A);
  • 100 percent of the noncontinuous non-motor load ;

125 percent of the continuous non-motor load .

The 125 percent applies to only one motor — the highest rated. Where two or more motors of the same rating are the largest, only one is taken at 125 percent.

430.25 Multimotor and Combination-Load Equipment. The ampacity of the conductors supplying multimotor and combination-load equipment shall not be less than the minimum circuit ampacity marked on the equipment.

430.26 Feeder Demand Factor. Where reduced heating of the conductors results from motors operating on duty-cycle, intermittently, or from all motors not operating at one time, the authority having jurisdiction may grant permission for feeder conductors to have an ampacity less than specified in 430.24.

430.28 Feeder Taps. Feeder tap conductors shall have an ampacity not less than that required by Part II, shall terminate in a branch-circuit protective device, and shall meet one of three length and ampacity conditions: not over 10 feet long and having an ampacity at least one tenth of the feeder rating; not over 25 feet long with an ampacity at least one third of the feeder conductors; or the same ampacity as the feeder conductors.

Worked Example — Single Motor Conductors

A 460-volt, three-phase, 30 horsepower continuous-duty motor with a nameplate FLA of 38 amperes and a service factor of 1.15. Table 430.250, 30 hp at 460 V ......... FLC = 40 A

  • Conductor ampacity, 430.22 ............ 40 x 1.25 = 50 A
  • Table 310.16, 75 C copper ............. 8 AWG = 50 A -> acceptable

Notice that the nameplate 38 amperes is not used for the conductor. The table FLC of 40 amperes is.

Worked Example — Several Motors

A feeder supplies three 460-volt three-phase motors: 30 hp (FLC 40 A), 10 hp (FLC 14 A), and 5 hp (FLC 7.6 A), plus 12 amperes of continuous lighting load. 125% of largest motor ......... 40 x 1.25 = 50.0 A

  • Other motors at 100% .......... 14 + 7.6 = 21.6 A
  • 125% of continuous other load . 12 x 1.25 = 15.0 A
  • ------
  • Minimum feeder ampacity .................... 86.6 A
  • Overload Protection — Part III

Overload protection guards against sustained operating current above rating — a jammed conveyor, a failed bearing, a motor running in a hot enclosure. It is not short-circuit protection.

430.31 General. Part III specifies overload devices intended to protect motors, motor-control apparatus, and motor branch-circuit conductors against excessive heating due to motor overloads and failure to start. Overload is not intended to protect against short-circuit or ground-fault currents.

430.32(A) Continuous-Duty Motors — More Than 1 Horsepower. Each continuous-duty motor rated more than 1 horsepower shall be protected against overload by one of the following means:

(A)(1) Separate Overload Device. A separate overload device that is responsive to motor current. This device shall be selected to trip or shall be rated at no more than the following percent of the motor nameplate full-load current rating :

  • Motor characteristic Percent of nameplate FLA
  • Motors with a marked service factor 1.15 or greater 125 percent
  • Motors with a marked temperature rise 40 degrees C or less 125 percent
  • All other motors 115 percent

(A)(2) Thermal Protector. A thermal protector integral with the motor, approved for use with the motor it protects, that will prevent dangerous overheating due to overload and failure to start.

(A)(3) Integral with Motor. A protective device integral with a motor that will protect the motor against damage due to failure to start.

(A)(4) Larger Than 1500 Horsepower. A protective device integral with the motor that is responsive to motor temperature.

430.32(B) Continuous-Duty Motors — 1 Horsepower or Less, Not Permanently Installed. Shall be permitted to be protected by the branch-circuit short-circuit and ground-fault protective device where the motor is manually started and within sight from the controller.

430.32(C) Selection of Overload Relay. Where the sensing element or setting or sizing of the overload device selected in accordance with 430.32(A)(1) and (B)(1) is not sufficient to start the motor or to carry the load , higher size sensing elements or incremental settings or sizing shall be permitted, provided the trip current of the overload device does not exceed the following percentage of motor nameplate full-load current rating:

  • Motor characteristic Maximum percent
  • Service factor 1.15 or greater 140 percent
  • Temperature rise 40 degrees C or less 140 percent
  • All other motors 130 percent

430.36 Fuses — In Which Conductor. Where fuses are used for motor overload protection, a fuse shall be inserted in each ungrounded conductor and also in the grounded conductor if the supply system is 3-wire, 3-phase AC with one conductor grounded.

430.37 Devices Other Than Fuses — In Which Conductor and Table 430.37 specify the number and location of overload units for each system type — for example, a three-phase AC motor requires three overload units, one in each phase.

Worked Example — Overload Sizing

A continuous-duty motor has a nameplate FLA of 28 amperes and a marked service factor of 1.15. What is the maximum initial overload device rating, and what is the maximum after adjustment under 430.32(C)? Initial, 430.32(A)(1) ........ 28 x 1.25 = 35.0 A

Maximum adjusted, 430.32(C) .. 28 x 1.40 = 39.2 A

Note that both use the nameplate 28 amperes , not a table value. That is the one place in Article 430 where nameplate governs, and questions are written specifically to test whether you know it.