Master Electrician Practice
Chapter XI

Motors

Master Electrician Practice study guide with diagrams.

Motors

Learning Objectives

Upon completing this chapter, you will be able to:

Apply the general requirements for motor installations, including nameplate data, terminal housings, and motor disconnecting means.
Size motor branch-circuit conductors, short-circuit and ground-fault protection, and overload protection correctly for single and multiple motor applications.
Calculate feeder conductor and protection requirements for groups of motors per the 2026 NEC.
Identify the specific rules for motor controllers, control circuits, and adjustable-speed drive systems.
Navigate the NEC efficiently to locate motor-related requirements across Articles 430, 440, and 445.
Recognize common field inspection failures and exam traps related to motor installations.

1.1 Scope and General Requirements (Article 430)

Article 430 governs the installation of motors, motor circuits, and controllers. It is one of the most heavily tested articles on the Master exam because it integrates conductor sizing, protection, and control into a single system. The article is divided into parts that cover: general (Part I), motor circuit conductors (Part II), overload protection (Part III), branch-circuit short-circuit and ground-fault protection (Part IV), feeders (Part V), motor control circuits (Part VI), controllers (Part VII), and disconnecting means (Part IX).

Key general requirements:

Part-winding motors: Where a motor is arranged for part-winding starting, each motor winding must have its own branch-circuit short-circuit and ground-fault protective device, and its own disconnecting means. The combined rating of the devices must not exceed the rating permitted for a single motor.
Terminal housings: Motor terminal housings must be of metal or other approved material, and must be mounted so that they are not likely to work loose. For motors over 100 hp or for motors with larger than No. 1 AWG conductors, the terminal housing must be of substantial construction.
Marking: Each motor must have a nameplate showing the manufacturer's name, rated volts, full-load current, and other required data. The nameplate is the legal basis for all calculations — never guess from horsepower tables when a nameplate is available.

1.2 Motor Circuit Conductors (Part II)

1.2.1 Branch-Circuit Conductor Sizing — 430.22

Motor Branch Conductors — NEC 430.22 Master Depth Motor Branch Conductors — NEC 430.22 Master Depth: 125% FLC from Tables 430.247–430.250 460V 3-Phase Disconn. 430.109 Controller 430.83 MOTOR 25 hp STEP 1 — Find FLC Table 430.250: 25 hp @ 460V 3-phase → FLC = 34 A Never use nameplate amperes! STEP 2 — 125% of FLC 34 A × 1.25 = 42.5 A NEC 430.22(A) — branch circuit conductor ampacity ≥ 125% FLC STEP 3 — Select Conductor Table 310.16, 75°C column (per 110.14(C)) → 8 AWG Cu Rated 50 A ≥ 42.5 A ✓ ⚠ TRAP 1 Using nameplate amperes instead of Table FLC Nameplate = motor design data, not NEC ampacity basis ⚠ TRAP 2 125% after wire selection (wrong order) Calculate ampacity first, then select conductor ⚠ TRAP 3 Using 430.52 breaker logic for conductor sizing 430.52 = OCPD, not conductors! KEY CODE REFERENCES • 430.22(A): Branch circuit conductors ≥ 125% of motor FLC • Table 430.250: Motor FLC values (not nameplate) • Table 310.16: Conductor ampacity 75°C column per 110.14(C) • 110.14(C): Temperature limits termination ratings • 430.52: OCPD sizing (separate) inverse-time breaker: 250% FLC max — not conductor sizing • 430.6: FLC from tables, nameplate only for overload WHY 8 AWG NOT 10 AWG? 10 AWG 75°C = 35 A — too small 8 AWG 75°C = 50 A ≥ 42.5 A ✓ Next standard size above 42.5 A ✓ 8 AWG Cu @ 75°C → 50 A ampacity (Table 310.16) Master Electrician Practice — NEC 430.22 Motor Branch Conductors | Colorado DORA / PSI | 2026 NEC

Branch-circuit conductors supplying a single motor must have an ampacity of not less than 125% of the motor's full-load current (FLC) . The FLC is determined from Table 430.247 (direct-current motors), Table 430.248 (single-phase alternating-current motors), Table 430.250 (three-phase alternating-current motors), or the motor nameplate — whichever is applicable. For general motor applications, use the tables; for specific motors with a service factor of 1.15 or greater, or a temperature rise of 40°C or less, the nameplate current may be used for overload sizing but not for conductor sizing.

Critical distinction: For conductor sizing, use the table FLC. For overload protection, use the nameplate full-load current. This is a classic exam trap — mixing these two values leads to incorrect answers.

1.2.2 Conductors for Multiple Motors — 430.24

Where two or more motors are supplied by a single branch circuit, the conductor ampacity must be the sum of 125% of the highest-rated motor FLC plus 100% of the FLC of all other motors on that circuit. This same rule applies to feeder conductors supplying multiple motors.

1.2.3 Motor and Other Loads — 430.25

Where a feeder supplies motor load(s) and other loads (lighting, heating, etc.), the conductor ampacity must be the sum of:

125% of the highest-rated motor FLC,
100% of the FLC of all other motors,
100% of the other loads, computed per Article 220.

1.2.4 Wye-Start, Delta-Run Motors — 430.22(C)

For wye-start, delta-run motors, the branch-circuit conductors must have an ampacity of not less than 125% of the motor's FLC. However, the controller and the overload devices must be selected based on the motor's full-load current, not the reduced starting current.

1.3 Overload Protection (Part III)

1.3.1 General Rule — 430.32

Each motor must be protected against overload by a separate overload device that is responsive to motor current. The device must be sized at:

Not more than 125% of the motor nameplate full-load current rating for motors with a marked service factor of 1.15 or greater, or with a marked temperature rise of 40°C or less.
Not more than 115% of the nameplate current for all other motors.

1.3.2 Permitted Increase — 430.32(C)

Where the specified overload device sizes do not correspond to standard sizes, the next higher standard size may be used. However, the next higher size must not exceed:

140% of the nameplate current for motors with service factor ≥ 1.15 or temperature rise ≤ 40°C,
130% for all other motors.

If the next higher standard size still exceeds these limits, a qualified person must determine that the motor is protected — this is a supervisory decision, squarely in the Master's domain.

1.3.3 Overload Relays and Other Devices — 430.36, 430.37

Overload relays and other devices must be selected to trip at the motor's rated current. Where separate overload relays are used, the setting must be based on the nameplate current. Dual-element fuses may be used for overload protection only where they are sized per 430.32 and are part of a listed combination motor controller.

1.4 Branch-Circuit Short-Circuit and Ground-Fault Protection (Part IV)

1.4.1 Rating or Setting — 430.52

Motor Branch Short-Circuit and Ground-Fault Protection — 430.52(C)(1) Master Depth Motor Branch Short-Circuit & Ground-Fault Protection NEC 430.52(C)(1) — Maximum Device Rating vs. Starting Current | 2026 NEC Supply 240V 3Ø SC/GF Device (Breaker/Fuse) M 25 HP 3Ø FLC = 34A per Table 430.250 (not nameplate) Table 430.52(C)(1) — Maximum Branch SC/GF Device Rating Device Type % of FLC Max Rating Code Reference Inverse-time Brkr 250% 85A 430.52(C)(1) row 1 Non-TD Fuse 300% 102A → 110A 430.52(C)(1) row 3 Time-Delay Fuse 175% 59.5A → 60A 430.52(C)(1) row 2 Calculations: 34A × 250% = 85A | 34A × 300% = 102A → next std 110A | 34A × 175% = 59.5A → next std 60A ✓ Next-standard-size rule (430.52(C)(1) Ex. 1): If starting current trips a lower device, you may go up to the next standard size — but NEVER exceed 400% for breaker (430.52(C)(1) Ex. 1). ⚠ TRAP: (1) FLC source is Table 430.250, not the nameplate. (2) SC/GF device does NOT protect the motor from overload — overload relays (430.32) do that. (3) 240.4(G) removes motor circuits from 240.4(B) conductor rules. Master Electrician Practice — NEC 430.52 Motor Branch Circuit Protection | Colorado DORA / PSI 2026

The branch-circuit short-circuit and ground-fault protective device (SCGFP) must be capable of carrying the motor's starting current and must be sized per Table 430.52. The table provides maximum percentages of motor FLC for different types of protective devices:

Motor TypeNontime-Delay FuseDual-Element (Time-Delay) FuseInstantaneous Trip BreakerInverse-Time Breaker
AC polyphase (squirrel cage, etc.)300%175%800%250%
Wound-rotor300%175%800%250%
DC (constant speed)150%150%250%150%

Note: These percentages apply to the table FLC, not the nameplate current.

1.4.2 Next Higher Standard Size — 430.52(C)(1) Ex. 1

Where the calculated value does not correspond to a standard fuse or breaker size, the next higher standard size is permitted. However, the next higher size must not exceed 400% for nontime-delay fuses and instantaneous trip breakers, or 225% for time-delay fuses and inverse-time breakers. If the required protection exceeds these caps, the next lower standard size must be used.

1.4.3 Motor and Motor-Control Apparatus — 430.53

A single branch circuit may supply a motor and other motor-control apparatus where:

The branch-circuit SCGFP does not exceed the rating permitted for the smallest motor on the circuit, or
The group installation is protected by a listed combination motor controller, or
The branch circuit supplies a motor and a motor controller where the controller is within sight of the motor.

1.5 Feeder Protection and Sizing (Part V)

1.5.1 Feeder Conductors — 430.24 (reviewed above)

Feeder conductors must have an ampacity sufficient to carry the sum of 125% of the largest motor FLC plus 100% of all other motors and loads.

1.5.2 Feeder Short-Circuit and Ground-Fault Protection — 430.62

Multi-Motor Feeder SC/GF — NEC 430.62 Master Depth Multi-Motor Feeder Short-Circuit & Ground-Fault Protection NEC 430.62(A) — Feeder SC/GF device = largest branch device + FLC of all other motors Motor M1 — 10 hp FLC = 14 A (Table 430.248) Inverse-time breaker 250% per 430.52(C)(1) Motor M2 — 7.5 hp FLC = 11 A (Table 430.248) Inverse-time breaker 250% per 430.52(C)(1) Motor M3 — 5 hp FLC = 7.6 A (Table 430.248) Inverse-time breaker 250% per 430.52(C)(1) Branch devices: M1: 35 A | M2: 30 A | M3: 20 A NEC 430.62(A) Calculation Step 1 — Largest branch device: M1: 14 A × 250% = 35 A Step 2 — Add FLC of others: 35 A + 11 A + 7.6 A = 53.6 A Step 3 — Standard size per 240.6(A): Feeder breaker = 60 A Step 4 — Cross-check conductors: NEC 430.24: 125% × 14 + 11 + 7.6 = 17.5 + 11 + 7.6 = 36.1 A → Use Table 310.16, 60°C col. → 8 AWG Cu at 40 A ≥ 36.1 A ✓ ✓ 60 A feeder breaker protects 8 AWG conductors (40 A ≥ 36.1 A) FEEDER 60 A Inverse-time 60 A Conductors: 8 AWG Cu @ 60°C 40 A ≥ 36.1 A ✓ Feeder loads M1: 14 A M2: 11 A M3: 7.6 A Total: 32.6 A ⚠ COMMON TRAPS ✗ Summing nameplate currents ✗ Applying 250% to every motor ✗ Using branch device for feeder Use FLC table values, not nameplate ⚠ NEC Reference Chain 430.62(A) → 430.52(C)(1) 430.24 → Table 430.248 240.6(A) → Table 310.16 430.63: 60A also protects feeder Master Electrician Practice — NEC 430.62 Multi-Motor Feeder SC/GF | Colorado DORA / PSI | 2026 NEC

The feeder SCGFP must be sized at not greater than the largest branch-circuit SCGFP for any motor on the feeder, plus the sum of the FLCs of all other motors on the feeder. This is a two-step calculation:

66.Identify the largest branch-circuit SCGFP (per 430.52).
67.Add the FLC of all other motors.

The result is the maximum feeder protection rating. If this does not correspond to a standard size, the next lower standard size must be used — note the contrast with branch circuits where the next higher is permitted.

1.5.3 Motor Feeder Taps — 430.28

Motor feeder taps are permitted where the tap conductors have an ampacity of at least one-third of the feeder overcurrent device rating, are not longer than 25 ft, and terminate in a single overcurrent device or a motor controller with overload protection.

1.6 Motor Control Circuits (Part VI)

1.6.1 Overcurrent Protection — 430.72

Motor control circuits (e.g., push-button stations, relay coils) must be protected against overcurrent. Where the control circuit is tapped from the motor branch circuit, the protection must not exceed the branch-circuit SCGFP rating. For control circuits supplied from a separate source, the protection must be sized per Table 430.72(B) , which provides maximum ratings based on conductor ampacity.

1.6.2 Control Circuit Transformers — 430.72(C)(4)

Where a control circuit transformer supplies only the motor controller, the transformer must be protected by an overcurrent device rated at not more than 500% of the transformer's rated primary current. This is a common field inspection point.

1.7 Controllers and Disconnecting Means (Parts VII and IX)

1.7.1 Controller Requirements — 430.81 through 430.91

Each motor must have a controller capable of starting and stopping the motor and interrupting the stalled-rotor current. The controller must have a horsepower rating not less than the motor's horsepower rating at the applied voltage. For motors over 100 hp, the controller must be marked with the motor's horsepower and voltage.

Exception: A controller with a lower horsepower rating may be used where the controller is part of a listed combination motor controller, or where the motor is a resistance-type or impedance-type motor and the controller is suitable.

1.7.2 Disconnecting Means — 430.102 through 430.110

Location: A disconnecting means must be located in sight from the motor and the driven machinery. "In sight" means within 50 ft and visible.
Type: The disconnecting means must be a motor-circuit switch, molded-case circuit breaker, or other approved means. For motors over 100 hp, the disconnecting means must be a motor-circuit switch or circuit breaker.
Rating: The disconnecting means must have an ampere rating of at least 115% of the motor FLC (430.110). For a group of motors, the rating must be at least 115% of the sum of all motor FLCs.

1.8 Adjustable-Speed Drive Systems — 430.120 through 430.130

The 2026 NEC includes expanded requirements for adjustable-speed drive (ASD) systems, also known as variable-frequency drives (VFDs).

Conductors: The branch-circuit conductors supplying an ASD must be sized at 125% of the rated input current of the ASD (not the motor FLC). The ASD nameplate input current is the governing value.
Overload protection: The ASD must provide motor overload protection per 430.32, unless the drive is listed for the specific motor and the motor is marked accordingly.
SCGFP: The branch-circuit SCGFP must be sized per the ASD manufacturer's instructions and the drive's listed rating, not per Table 430.52.
Disconnecting means: The disconnecting means must be rated for the ASD input current and must be capable of interrupting the rated current of the drive.

Master-level note: When supervising VFD installations, verify that the drive's input current rating, not the motor nameplate, is used for conductor and protection sizing. This is a frequent source of undersizing.

1.9 Air-Conditioning and Refrigeration Equipment (Article 440)

Article 440 applies to hermetic refrigerant motor-compressors and their associated equipment. These are treated as a special class of motor because the compressor is sealed and the nameplate current (RLA — rated load amperes) is the governing value.

Branch-circuit conductors: Sized at 125% of the RLA (440.32).
SCGFP: Sized per 440.22, with maximums of 175% for time-delay fuses and 225% for inverse-time breakers of the RLA, with the next higher standard size permitted.
Overload protection: Must protect the compressor against overload per 440.52, using the RLA and the manufacturer's specified maximum overcurrent protection (MOP).

1.10 Generators (Article 445)

Generators are separately derived systems and must comply with Article 445 as well as the grounding requirements of Article 250.

Conductors: Generator conductors must be sized at 115% of the generator's rated output current (445.13).
Overcurrent protection: Generators must be protected against overcurrent per 445.18. Where the generator is a separately derived system, the neutral must be grounded per 250.30.
Disconnecting means: A disconnecting means must be provided for all ungrounded conductors, per 445.18(B).

1.11 Code Navigation — Where to Find It

TopicLocation
Motor general requirementsArticle 430, Part I
Motor circuit conductors430.22, 430.24, 430.25
Motor FLC tablesTables 430.247, 430.248, 430.250
Overload protection430.32, 430.36
Branch-circuit SCGFP430.52, Table 430.52
Feeder conductors and protection430.24, 430.62
Motor control circuits430.71–430.74
Controllers430.81–430.91
Disconnecting means430.102–430.110
Adjustable-speed drives430.120–430.130
Hermetic compressors (A/C)Article 440
GeneratorsArticle 445
Grounding of separately derived systems250.30
Standard fuse/breaker sizes240.6

1.12 Inspection and Supervision Points

As a Master electrician, you are responsible for the final sign-off. Verify the following on every motor installation:

112.Conductor ampacity — Confirm that branch-circuit conductors are sized at 125% of the table FLC, not the nameplate current.
113.Overload protection — Verify that overloads are sized per the nameplate current, not the table FLC.
114.SCGFP — Check that the branch-circuit fuse or breaker does not exceed Table 430.52 percentages, and that the next-higher-size exception was applied correctly.
115.Feeder protection — Confirm the feeder SCGFP is not greater than the largest branch-circuit device plus the sum of other motor FLCs, and that the next lower standard size was used when necessary.
116.Disconnecting means — Ensure the disconnect is in sight of the motor, is rated at least 115% of the motor FLC, and is capable of interrupting the motor's locked-rotor current.
117.Controller rating — Verify the controller horsepower rating matches or exceeds the motor rating.
118.VFD installations — Confirm conductors and protection are based on the drive's input current rating, not the motor FLC.
119.Grounding — For separately derived systems (generators, transformers supplying motor control circuits), verify the neutral is grounded per 250.30.

1.13 Common Exam Traps

Using nameplate current for conductor sizing — Always use Table 430.248 or 430.250 for conductors.
Using table FLC for overloads — Always use nameplate current for overloads.
Applying the next-higher rule to feeders — Feeders use the next lower standard size; branch circuits use the next higher.
Forgetting the 125% factor for the largest motor — This applies to both branch circuits and feeders.
Confusing RLA with FLC — For hermetic compressors, use RLA per Article 440, not the general motor tables.
Oversizing VFD protection — Table 430.52 does not apply to ASD input circuits; use the drive's listed rating.
Ignoring the 50-ft "in sight" rule — A disconnect beyond 50 ft from the motor is not "in sight."

Summary

Motor installations require a systematic approach: identify the motor type, determine the correct FLC source (table vs. nameplate), size conductors at 125%, protect against overload per nameplate, and coordinate branch-circuit and feeder SCGFP per Article 430. The Master electrician must also supervise VFD systems, hermetic compressors, and generator installations, all of which have distinct rules. Mastery of the tables and the exceptions — especially the next-higher versus next-lower rules — is essential for both the exam and real-world code compliance.

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