A free NEC Article 430 practice test for the journeyman exam: 74 questions on Motors, Motor Circuits, and Controllers, each with the answer and the why behind it.
These 74 journeyman-exam practice questions cover NEC Article 430 across 74 code concepts, every one with the correct answer and a plain-English explanation of the rule behind it. They come from the same question bank the Loomi app trains you on — this is the free web sample, not a separate watered-down set.
Work straight down the sheet and answer before you peek: each question hides its answer behind Show answer & explanation. Questions tagged Code lookup are speed drills — race your codebook to the cited section. Printing this page gives you a clean paper worksheet with the answers left off.
Every motor calculation starts from the full-load current in Table 430.250/430.248 — not the nameplate. Branch-circuit conductors carry 125% of FLC (430.22); the branch OCPD is a table percentage of FLC, rounded up to the next standard size (430.52).
What is the full-load current of a 10 HP, 230-volt, three-phase induction motor? (NEC Table 430.250)
Correct: D — 28 A
Table 430.250 lists the full-load current of a 10 HP three-phase motor at 230 V as 28 A. The distractors are the FLC at other voltage columns — read the column for the motor's actual voltage.
Size conductors from the NEC's motor tables for normal motors, but use the nameplate current instead for low-speed, high-torque, multispeed, or torque motors.
When sizing branch-circuit conductors for a standard general-purpose motor, which current value should be used per 430.6(A)(1)?
Correct: B — The value from Table 430.247, 430.248, 430.249, or 430.250
Per 430.6(A)(1), conductor ampacity, switch ratings, and branch-circuit protection for general motor applications are based on the values in Table 430.247-430.250, not the nameplate current. Nameplate current and locked-rotor current apply to special cases like torque motors and overload protection, not general conductor sizing.
The nameplate code letter reflects locked-rotor kVA per hp under the worst-case condition the motor can actually start in — not just a single fixed rating.
You're checking a motor nameplate to decode the locked-rotor kVA per horsepower from its single letter marking. Which section contains the reference table that translates that letter into a kVA/hp range?
Correct: B — 430.7(B)
Table 430.7(B) lives at 430.7(B) and lists the locked-rotor indicating code letters with their kVA/hp ranges. 430.6(A)(1) instead governs using ampacity table values for conductor sizing, not code-letter decoding.
Motor terminal housings must be metal (or noncombustible nonmetal with internal bonding), sized per Table 430.12(B)/(C) for field wiring, and always provide a place to land the equipment grounding conductor.
A motor is installed in an ordinary (non-hazardous) location. Under what condition is a nonmetallic terminal housing permitted?
Correct: B — It is noncombustible and has an internal grounding means between the motor frame and the grounding connection
Per 430.12(A), nonmetallic housings are allowed outside hazardous (classified) locations only when substantial, noncombustible, and fitted with an internal grounding means between the motor frame and the equipment grounding connection. UV rating, motor horsepower, and GFCI protection are not the qualifying conditions in this section.
A continuous-duty motor over 1 hp needs one of four listed overload protection methods, most commonly a separate overload device sized off the nameplate current.
A 5 hp motor operates in a continuous-duty application. Per 430.32(A), which of the following is an approved method of overload protection?
Correct: C — A separate overload device responsive to motor current, sized per the motor nameplate full-load current
A separate overload device responsive to motor current and sized off the nameplate full-load current is one of the four permitted methods under 430.32(A)(1). Short-circuit protection alone does not satisfy overload protection requirements. A thermal protector must be approved to prevent dangerous overheating from overload and failure to start, not just sized to locked-rotor current. Embedded temperature detectors under 430.32(A)(4) apply only to motors larger than 1500 hp, not simply any motor over 1 hp.
Size the branch-circuit SCPD from the motor's full-load current using 430.52 — unless the drive is listed and marked "Suitable for Output Motor Conductor Protection," and never exceed a rating the manufacturer marks on the equipment.
A single motor is fed through a variable frequency drive that is NOT marked "Suitable for Output Motor Conductor Protection." How must the branch-circuit short-circuit and ground-fault protective device be sized?
Correct: D — From the motor's full-load current rating per 430.6, applied to 430.52(C)(1), (C)(3), (C)(5), or (C)(6)
Per 430.130(A)(1), absent the special listing/marking, protection rating and type are determined using the motor's full-load current rating from 430.6(A) or (B) applied through 430.52. Sizing from the drive's rated input current is only permitted when the equipment is listed and marked "Suitable for Output Motor Conductor Protection."
When an adjustable-speed drive can't keep the motor at nameplate current across its speed range, overtemperature protection is required in addition to normal conductor overload protection.
A motor is fed by an adjustable-speed drive and is not rated to operate at nameplate current across the full speed range the application requires. Per 430.126(A), what must be provided?
Correct: D — Overtemperature protection, in addition to the conductor protection already required by 430.32
430.126(A) requires overtemperature protection in addition to the conductor protection required in 430.32, because reduced-speed operation can overheat the motor even below its rated current. Conductor protection alone doesn't address this, and disconnect sizing or group protection are separate requirements not addressed by this section.
Size the motor branch-circuit protective device from Table 430.52(C)(1) as a percentage of full-load current, rounding up to the next standard rating, then raising it further only if starting current trips it.
What is the primary purpose of the motor branch-circuit short-circuit and ground-fault protective device sized under 430.52?
Correct: A — To protect the branch-circuit conductors and equipment from short circuits and ground faults while carrying starting current
430.52 governs the branch-circuit short-circuit and ground-fault protective device, which per 430.52(B) must be capable of carrying starting current while protecting against faults. Overload protection is a separate requirement (covered elsewhere in Article 430), not the function of this device.
A feeder OCPD for an all-motor group is sized at the largest single branch-circuit protective device rating plus the full-load currents of all other motors.
A feeder supplies three motors, each with its own branch-circuit short-circuit and ground-fault protective device sized under 430.52. Per 430.62(A), how is the feeder protective device rated?
Correct: B — Equal to the largest branch-circuit device rating among the three, plus the full-load currents of the other two motors
430.62(A) sets the feeder OCPD at the largest branch-circuit short-circuit/ground-fault device rating for any motor in the group, plus the full-load currents of the other motors in that group — not a simple sum of FLCs or of all the branch-circuit ratings, and not just 125% of one motor's FLC (that's a branch-circuit concept, not the feeder rule).
A motor feeder tap skips full feeder-size conductors only if it fits one of three length/ampacity/protection combos in 430.28.
An electrician installs a 10-ft feeder tap in a raceway, protected on the line side by an overcurrent device rated well above the tap conductor's ampacity. What limit applies to that line-side overcurrent device under 430.28(1)?
Correct: B — It cannot exceed 1000 percent of the tap conductor's ampacity
430.28(1) caps the line-side overcurrent device at 1000% of the tap conductor's ampacity for the 10-ft tap option. The one-third ampacity figure belongs to the 25-ft tap option in 430.28(2), the 125% FLC figure is a motor branch-circuit sizing rule, and matching feeder ampacity describes the third, no-length-limit tap option under 430.28(3).
A motor can skip individual overload protection only at 1 hp or less under 430.32 limits; above that, the motor's own overload device is required.
A small motor is connected to a general-purpose branch circuit with no individual overload protection installed. Under which condition is this acceptable?
Correct: A — The motor is rated 1 hp or less and complies with 430.32(B), 430.32(D), and 430.53(A)(1) and (A)(2)
430.42(A) permits omitting individual overload protection only for motors at or below the 1 hp threshold that meet the limiting conditions in 430.32(B), 430.32(D), and 430.53(A)(1)-(A)(2). Time delay (430.42(D)) and group-installation approval (430.42(B)) address different requirements and don't by themselves justify skipping overload protection, and cord-and-plug connection alone doesn't remove the horsepower limit.
An instantaneous-trip breaker (MCP) can protect a motor branch circuit only inside a listed combination controller, adjusted per Table 430.52(C)(1) or higher only under specific exceptions.
Under what condition does 430.52(C)(3) permit the use of an instantaneous-trip circuit breaker for motor branch-circuit protection?
Correct: A — It must be adjustable and part of a listed combination motor controller with coordinated overload and short-circuit/ground-fault protection
430.52(C)(3)(a) requires the instantaneous-trip breaker (MCP) to be adjustable and part of a listed combination motor controller that coordinates motor overload protection with the breaker's short-circuit and ground-fault protection — the MCP itself provides no overload protection. The 8 A full-load current option is only a special setting allowance under 430.52(C)(3)(b)(3), not a condition for using an MCP at all.
Control conductors only need short-circuit and ground-fault protection, and the motor branch-circuit protective device can often provide it — but the allowed rating depends on whether conductors stay inside the enclosure or leave it.
A motor control circuit's conductors run inside the motor control equipment enclosure only, and the designer wants to rely on the motor branch-circuit short-circuit and ground-fault protective device for their protection instead of adding separate overcurrent devices. Which section's table gives the maximum protective device rating permitted for conductors that stay within the enclosure?
Correct: D — 430.72(B)(2)
430.72(B)(2) hosts Table 430.72(B)(2), which gives Column B ratings for control conductors protected by the motor branch-circuit device and not extending beyond the enclosure. 430.72(B)(1) applies only when separate overcurrent protection is required because the branch-circuit device doesn't qualify under (B)(2), so it doesn't govern this enclosure-only scenario.
A control circuit transformer must be protected by one of five permitted methods in 430.72(C), unless opening the circuit itself would create a hazard.
A control circuit transformer supplies the control circuit for a fire pump motor. What does 430.72(C) require for overcurrent protection?
Correct: C — Overcurrent protection is permitted to be omitted because opening the circuit would create a hazard
430.72(C) states overcurrent protection shall be omitted where opening the control circuit would create a hazard, citing a fire pump motor's control circuit as the example. The 500% primary device and Part II of Article 725 are protection methods used when protection IS required, and 450.3 is the general transformer protection option under 430.72(C)(2) — none apply once the hazard exception takes over.
Treat every motor plus resistance load on a shared disconnect as one giant motor: add full-load currents for the rating, add locked-rotor currents for starting, then apply 115%.
Two motors and a resistance heater share a single disconnecting means and can operate simultaneously. How must the disconnect's rating be determined per 430.110(C)?
Correct: A — Treat the combined full-load and locked-rotor currents of all loads as if they were a single motor
430.110(C)(1) requires summing full-load currents and locked-rotor currents of every motor and resistance load, then treating that combined figure as a single motor for disconnect sizing. Sizing to just the largest motor, or skipping the locked-rotor sum, ignores the simultaneous-load requirement in 430.110(C).
One device can serve as both motor controller and disconnecting means only if it opens all ungrounded conductors, is overcurrent-protected, and is one of three approved types.
An electrician wants to use a single inverse time circuit breaker as both the motor controller and the disconnecting means. Which condition must also be satisfied for this to comply with 430.111?
Correct: A — The breaker must open all ungrounded conductors to the motor and be protected by an overcurrent device in each ungrounded conductor
Per 430.111(A), any device used as both controller and disconnecting means must open all ungrounded conductors to the motor and be protected by overcurrent devices in each ungrounded conductor. An inverse time breaker used this way must still be operable directly by hand per 430.111(B)(2), so power-operable-only fails that requirement. Autotransformer controllers are excluded from dual-role use entirely, and there's no NEC requirement tying the device's location to the motor terminal housing.
The motor itself needs a disconnect in sight from it and the driven machinery, unless the controller disconnect already sits in that sightline and is lockable.
Under 430.102(B)(1), where must the disconnecting means for a motor be located?
Correct: D — Within sight from the motor location and the driven machinery location
430.102(B)(1) requires the motor's disconnecting means to be located in sight from both the motor location and the driven machinery location. A distance-only rule (like '50 ft') or 'same room' without sightline doesn't satisfy the requirement, and sight from the overcurrent device isn't the standard used here.
The motor controller disconnect must be in sight from the controller, with narrow exceptions for over-1000-volt circuits and valve actuator motor assemblies.
Under 430.102(A), where must the disconnecting means for a motor controller normally be located?
Correct: C — In sight from the motor controller
430.102(A) requires the disconnecting means to be located in sight from the motor controller. A distance-only rule, a same-room rule, or a lockable-anywhere rule are not what the section states; the lockable-out-of-sight option only applies under the specific over-1000-volt or VAM exceptions.
Every motor disconnecting means between the feeder/branch circuit and the motor must be one of the listed device types in 430.109(A) unless a specific exception in 430.109(B)–(G) applies.
Under the general rule of 430.109(A), which of the following is a listed device type permitted as a motor disconnecting means?
Correct: B — A listed molded case switch
430.109(A)(3) lists a listed molded case switch as an approved type. A general-use snap switch is not on the 430.109(A) list, an unmarked manual motor controller is excluded by 430.109(A)(6) (it must carry the 'Suitable as Motor Disconnect' marking), and fuse assemblies are not a disconnect type under this section.
Stationary motor frames must be grounded if fed by metal wiring, wet, hazardous-classified, or over 150V to ground; portable motor frames must be grounded or guarded only above 150V to ground.
A stationary motor is fed by nonmetallic wiring, is in a dry indoor location, is not in a hazardous location, and operates at 120 volts to ground. Does its frame need to be grounded under 430.242?
Correct: B — No, none of the triggering conditions apply
Per 430.242, grounding is required only if fed by metal-enclosed wiring, in an unguarded wet location, in a hazardous (classified) location, or over 150V to ground. None of these apply here, so the frame can instead be permanently insulated from ground — grounding is not mandatory.
Feeder ampacity for several motors equals 125% of the largest motor's FLC plus the sum of all other motor FLCs plus the non-motor loads (100% noncontinuous, 125% continuous).
A feeder supplies three motors of different full-load currents and no other loads. Per 430.24, how should the conductor ampacity be determined?
Correct: B — 125% of the full-load current of the highest-rated motor plus 100% of the full-load currents of the other motors
Under 430.24, only the highest-rated motor's full-load current is multiplied by 125%; every other motor in the group is added at 100% of its full-load current. Applying 125% to every motor, or to the whole sum, overstates the required ampacity, and swapping which motor gets the 125% factor reverses the rule.
Every motor needs its own controller unless it fits one of three group exceptions — same machine, shared overcurrent protection, or same room within sight.
Under 430.87, what is required for each motor unless a specific exception applies?
Correct: C — An individual motor controller
430.87 states each motor shall be provided with an individual motor controller. Shared overcurrent protection under 430.53(A) and a shared room are conditions that permit a single controller to serve a group — they are not requirements imposed on every motor. A branch-circuit disconnecting means may serve as the controller, but the base rule is about the controller itself, not a separate disconnect requirement.
Small motors rated 6 A or less can share one 20 A (120V) or 15 A branch circuit without individual branch-circuit protection, if controller ratings and overload protection are still met.
An electrician wants to place four small motors on one nominal 120-volt branch circuit protected at 20 amperes, relying on 430.53(A). Which condition must ALL four motors meet?
Correct: D — Each motor is rated not more than 1 hp and its full-load current does not exceed 6 amperes
430.53(A) requires every motor on the shared circuit to be rated not over 1 hp with a full-load rating not exceeding 6 amperes each — the limit applies to each motor individually, not just the largest one, and there's no 2 hp allowance under this exception.
Part X supplements — not replaces — Parts I through IX of Article 430, and the 1000-volt threshold decides whether Part X or Part XI governs a drive.
A 480V adjustable-speed drive feeds a single motor. The drive has a bypass contactor that allows the motor to run across-the-line if the drive faults out. Which section specifies the overload protection requirements that must still be provided for the motor when it's running through the bypass circuit?
Correct: A — 430.124(B)
430.124(B) Bypass Circuits specifically requires overload protection per Part III when a bypass device is used to run the motor across-the-line. 430.124(A) instead addresses overload protection already included in the power conversion equipment (no bypass involved), 430.126(B) covers overtemperature protection (not overload) for multiple motors, and 430.122(C) covers conductor sizing for the bypass device, not overload protection.
Output conductors from an adjustable-speed drive to the motor need at least 125% of motor full-load current, unless the drive is listed for output conductor protection with a marked minimum size.
A power conversion unit supplying a motor is listed and marked 'Suitable for Output Motor Conductor Protection.' How must the output conductor ampacity be determined?
Correct: A — Use whichever is larger: 125% of motor full-load current, or the ampacity of the minimum conductor size marked on the equipment
Per 430.122(B), when the power conversion equipment is listed and marked 'Suitable for Output Motor Conductor Protection,' the output conductor ampacity must be the larger of 125% of motor FLC or the marked minimum conductor size ampacity — not one or the other alone, and not simply the default 125% rule that applies to unlisted equipment.
Multiple motors (or motors plus other loads) can share one branch circuit only if every controller, overload device, and the circuit protection itself meet listing and sizing rules in 430.53(C)(1) through (C)(5).
Under 430.53(C), what must be true of each motor before several motors can be grouped onto a single branch circuit?
Correct: D — Each motor must have individual overload protection
430.53(C) permits grouping motors of any size (or motors with other loads) on one branch circuit specifically because each motor still carries individual overload protection. Requiring matched horsepower, omitting overload protection, or sharing overload protection across motors all contradict that core condition.
A grounded control circuit must be wired so a remote ground fault can't start the motor or defeat a shutdown device.
A remote motor control circuit has one conductor grounded. Per 430.74, the circuit's electrical arrangement must ensure that a ground fault remote from the controller will do what?
Correct: B — Neither start the motor nor bypass shutdown devices
430.74 requires that a ground fault in a grounded control circuit, occurring remote from the motor controller, will not start the motor and will not bypass manually operated or automatic safety shutdown devices. There is no NEC requirement in this section for a timed overload trip, automatic transfer to a backup controller, or an audible alarm — those are plausible-sounding but not what 430.74 mandates.
A control transformer mounted inside the motor controller enclosure must tap the load side of the disconnecting means, so opening the disconnect kills it too.
A motor control circuit uses a control transformer to step down voltage, and the transformer is mounted inside the motor controller's own enclosure. Which section specifies which side of the controller's disconnecting means this transformer must be connected to?
Correct: A — 430.75(B)
430.75(B) specifically governs a control transformer located inside the motor controller enclosure, requiring it to be connected to the load side of the disconnecting means. 430.72(C)(2) instead addresses overcurrent protection sizing for control circuit transformers generally, not disconnect-side placement, and doesn't apply when the transformer sits inside the controller enclosure itself.
Motor control circuits must be fully disconnected from every power source when the disconnect is open, whether that takes one device or several.
A wye-delta reduced-voltage motor controller enclosure has a control transformer feeding the motor control circuit. The panel has two separate disconnects — one for the motor/controller power and one for the control circuit — mounted immediately adjacent to each other as required. A designer wants to know which section actually requires that these two disconnects be located immediately adjacent to each other (absent the multi-conductor exception).
Correct: D — 430.75(A)
430.75(A) is the disconnection rule that requires separate motor and motor-control-circuit disconnects to be located immediately adjacent to each other (with the 12-conductor exception). 430.74 covers electrical arrangement of control circuits, not disconnect location, and 430.72(A) is general overcurrent protection — neither addresses disconnect placement.
Vertical sections of a motor control center are for terminating conductors only — busbars must be barrier-protected from anything just passing through, and gutter space follows Table 312.6.
An electrician wants to route feeder conductors horizontally through a vertical section of a motor control center on their way to a different section, without terminating anything there. What does 430.97(A) require?
Correct: C — The conductors must be isolated from the busbars by a barrier
430.97(A) permits conductors to travel horizontally through a vertical section only where they are isolated from the busbars by a barrier — it doesn't ban pass-through wiring, and it doesn't require relabeling as control wiring or termination in that section.
MCC buses run A, B, C front-to-back, top-to-bottom, or left-to-right, with B always the high leg on 4-wire delta systems.
Viewed from the front of a motor control center, what is the standard phase arrangement on the horizontal common power and vertical buses?
Correct: C — A, B, C from front to back, top to bottom, or left to right
Per 430.97(B), the standard phase arrangement is A, B, C from front to back, top to bottom, or left to right as viewed from the front of the MCC. C, B, A is only permitted for rear-mounted units on a shared vertical bus, not as the general standard, and a fixed order is required rather than being left to the manufacturer.
An MCC used as service equipment needs one main disconnect for all ungrounded service conductors, plus a main bonding jumper sized per 250.28(D) if a grounded conductor is present.
A motor control center is being installed as service equipment for a facility. Per 430.95, how must the ungrounded service conductors be disconnected?
Correct: C — By a single main disconnecting means for all ungrounded service conductors
430.95 requires a single main disconnecting means to disconnect all ungrounded service conductors when an MCC is used as service equipment. The 'up to six disconnects' rule applies to services generally under Article 230, not to this MCC-specific requirement; a disconnect per section and using the bonding jumper as a disconnect are not what this section describes.
A motor controller enclosure can't double as a junction box or raceway for other circuits, and its terminals need the minimum bending space set by Table 430.10(B).
You're installing a combination motor controller with disconnect and need to know the minimum wire-bending space required at the terminals for the conductor lugs being used. Which section provides this data?
Correct: C — 430.10(B)
430.10(B) hosts Table 430.10(B), the minimum wire-bending space table for enclosed motor controller terminals. 430.12(B) covers dimensions and space for wire-to-wire connections inside motor terminal housings, not controller enclosures, and 430.9(C) covers terminal torque requirements, not bending space.
Every motor controller needs manufacturer, voltage, current or hp rating, and SCCR — but SCCR marking has several valid exceptions.
A contractor is installing a combination motor controller for a 15 hp, 480V motor and needs to mark it with its short-circuit current rating along with the manufacturer's name, voltage, and current rating. Which section covers this marking requirement?
Correct: D — 430.8
430.8 requires motor controllers to be marked with the manufacturer's name, voltage, current or horsepower rating, and short-circuit current rating. 430.7 governs marking on motors themselves (not controllers), 430.9 covers controller terminal markings/torque, and 430.6 addresses conductor ampacity and motor rating determination, not controller nameplate marking.
A motor disconnecting means must be rated at least 115% of the motor's full-load current, or 115% of nameplate current for a torque motor.
Per 430.110(A), what is the minimum current rating required for a motor disconnecting means rated 1000 volts or less?
Correct: A — 115% of the motor full-load current rating
430.110(A) sets the minimum disconnect current rating at 115% of the motor's full-load current rating. The 125% figure is a common motor branch-circuit conductor and overload factor elsewhere in Article 430, and 100% or 80% would leave no margin, which the disconnect rule doesn't allow.
A motor fed from more than one source needs a disconnect for each source next to the equipment, plus warning signs cross-referencing the other disconnects.
A machine shop has a motor that can be powered either from the utility service or from an on-site standby generator, switched over as needed. A journeyman needs to identify the code requirement for disconnecting means at the equipment when a motor can receive power from either of these two separate sources. Which section governs this installation?
Correct: B — 430.113
430.113 specifically addresses motors receiving energy from more than one source, requiring a disconnecting means from each source immediately adjacent to the equipment (or a lockable controller disconnect per 110.25) plus warning signage. 430.112 by contrast covers the opposite case — multiple motors/loads served by a single disconnecting means — so it doesn't apply here.
A motor disconnect must open all ungrounded conductors together, show its position plainly, and never be able to close by itself.
Which statement correctly describes how a motor disconnecting means must operate per 430.103?
Correct: A — It must open all ungrounded supply conductors, and no pole can be operated independently
430.103 requires the disconnecting means to open all ungrounded supply conductors, with no pole operable independently. There's no allowance for sequential or single-conductor opening, and 430.105 actually requires the grounded-conductor pole (if present) to open simultaneously with the others, not first.
Every motor needs its own disconnect unless it fits one of three group exceptions in 430.112: single machine, shared branch-circuit protection under 430.53(A), or same room in sight of the disconnect.
Under 430.112, which situation permits a single disconnecting means to serve more than one motor?
Correct: C — The motors drive several parts of a single machine, such as a crane or hoist
430.112(1) permits one disconnect for motors driving several parts of a single machine or piece of apparatus, like cranes, hoists, or metal- and woodworking machines. Being in the same building but different rooms doesn't qualify — the 'single room, in sight' condition in 430.112(3) requires one room. Motor horsepower rating isn't a listed condition, and separate branch-circuit protection on each motor doesn't meet the shared-protection condition in 430.112(2), which requires one set of branch-circuit protective devices under 430.53(A).
Small stationary motors don't need a dedicated disconnect switch — the breaker, a general-use switch, or a listed manual controller can legally do the job.
A stationary motor rated at 15 hp needs a disconnecting means. Which option is permitted under 430.109(B)?
Correct: C — The branch-circuit overcurrent device serving the motor
Per 430.109(B), stationary motors of 18 hp or less can use the branch-circuit overcurrent device itself as the disconnecting means. The general-use switch, ac-dc snap switch, and listed manual controller options in 430.109(C) only apply at 2 hp or less, not 15 hp.
General-use switches, isolating switches, and cord-and-plug sets can serve as the motor disconnect — but only under the specific conditions each 430.109 exception spells out.
A stationary AC motor rated 125 hp needs a disconnecting means. Which option is explicitly permitted by 430.109(E)?
Correct: B — A general-use or isolating switch marked 'Do not operate under load'
430.109(E) permits a general-use or isolating switch for stationary motors rated more than 40 hp dc or 100 hp ac, but only when it is plainly marked 'Do not operate under load.' An unmarked general-use switch doesn't satisfy the exception, the plug-and-receptacle option belongs to cord-and-plug-connected motors under 430.109(F), and the 150 percent fuse/breaker condition is part of the autotransformer controller exception in 430.109(D), not this one.
A feeder supplying several motors must have an ampacity of at least 125% of the highest-rated motor's full-load current plus the sum of the full-load currents of all the other motors (430.24).
A feeder supplies 3 three-phase motors — 10, 25 and 50 HP at 460 V. What minimum feeder conductor ampacity does NEC 430.24 require?
Correct: D — 129.25 A
Full-load currents (Table 430.250): 14, 34, 65 A. 430.24: 125% of the largest (65 A) plus the rest — 1.25 × 65 + 48 = 129.25 A. Distractors skip the 125%, apply it to all motors, or to the wrong motor.
Bond the raceway or cable armor to a terminal housing junction box, which can sit up to 6 ft from the motor if flexible wiring methods with stranded leads connect the two.
A motor is wired with rigid metal conduit, and the junction box for the motor terminals is located 5 ft from the motor. Stranded leads run between the box and the motor within the conduit. Is this separation permitted?
Correct: B — Yes, because the raceway is bonded to both the motor and the box and the separation is within the 6 ft limit
Per 430.245(B), the junction box may be separated from the motor by not more than 1.8 m (6 ft) when stranded leads run through rigid metal conduit (among other listed flexible methods), with the raceway connected to both the motor and the box. Rigid metal conduit is explicitly permitted, and solid conductors are not allowed under this separation rule — leads must be stranded.
Exposed live parts at 50V or more must be guarded by enclosure or by location — height, room access, or platform — and if guarded only by location, attendants need insulating mats.
A 480-volt stationary motor without any commutator/brush assembly has exposed live terminals inside its terminal box, located in a general production area accessible to all plant employees, not elevated and not in a qualified-persons-only room. Which section specifies the acceptable methods (enclosure, location, or elevation) for guarding these live parts against accidental contact?
Correct: D — 430.232
430.232 lists the permitted guarding methods (qualified-persons-only room, elevated balcony/gallery/platform, or 2.5 m/8 ft elevation) for exposed live parts of motors/controllers at 50V or more. 430.233 only applies once 430.232's location-based guarding is used and an attendant needs access, addressing insulating mats/platforms rather than the guarding methods themselves.
Every motor nameplate must show manufacturer, volts, full-load current, speed, and time rating — plus horsepower, code letter, and protection markings once size or features trigger them.
A 25 hp, 460V polyphase wound-rotor induction motor is being nameplated at the factory. In addition to the standard markings, the technician needs to confirm what secondary-side electrical values must also appear on the nameplate. Which section lists this requirement?
Correct: C — 430.7(A)
430.7(A) item (10) requires wound-rotor induction motors to be marked with secondary volts and full-load current in addition to the primary nameplate data; 430.7(B) only covers locked-rotor code letters, not secondary voltage/current, and 430.9(A) covers controller/terminal markings, not motor nameplate content.
Motor and controller terminals must be clearly marked, wired with copper unless otherwise identified, and torqued to at least 0.8 N·m (7 lb-in) on small control-circuit screw terminals.
A screw-type pressure terminal on a control circuit device is being landed with a 14 AWG copper conductor. The terminal carries no torque marking. What minimum torque applies per 430.9(C)?
Correct: D — 0.8 N·m (7 lb-in)
430.9(C) sets a minimum torque of 0.8 N·m (7 lb-in) for screw-type pressure terminals used with 14 AWG or smaller copper conductors, unless the terminal itself is identified for a different value. There is no separate table referenced in this section, and a minimum does apply — it isn't optional.
Factory-wired multimotor equipment needs one nameplate with volts, phase, minimum circuit ampacity, and max protective device rating — figured with every simultaneous load counted.
A factory-wired piece of multimotor equipment must have a visible nameplate showing all of the following EXCEPT:
Correct: C — The individual full-load current of each motor inside the equipment
Per 430.7(D)(1), the nameplate must show manufacturer's name, voltage, frequency, phases, minimum supply conductor ampacity, and maximum protective device rating — a single combined ampacity and protective device figure, not a per-motor breakdown of individual full-load currents.
The disconnect for a motor controller over 1000V must match or exceed the circuit voltage, be lockable, and be rated at least 100% of the motor's (or drive's) full-load current — no sizing margin required, but no shortfall allowed either.
A high-voltage motor has a full-load current rating of 40 A. What is the minimum current rating required for its disconnecting means under 430.208?
Correct: D — 40 A
430.208 sets the minimum disconnect current rating at not less than 100 percent of the motor's full-load current rating — no additional 125% continuous-duty margin or 80% derating applies to this specific requirement, and the disconnect rating is independent of the short-circuit protective device rating.
Over-1000V motor circuits need a breaker or fuses that clear faults, disconnect safely without arc hazard, and don't auto-reclose unless faults are transient and safe.
A 2400-volt synchronous motor circuit is being protected with fuses installed in each ungrounded conductor to clear short-circuit and ground-fault current. Which section specifies the requirements for arranging these fuses so they cannot be serviced while energized and must be used with (or serve as) a suitable disconnecting means?
Correct: B — 430.206(C)(1)
430.206(C)(1) lists the two acceptable forms of fault-current protection for high-voltage motor circuits — a circuit breaker or fuses in each ungrounded conductor — and spells out the fuse servicing/disconnect requirements. 430.206(B)(1) instead covers the type of overload device permitted, a different protection function.
Over 1000V motors need thermal or current-sensing overload protection sized under engineering supervision, and it must trip all ungrounded conductors together without unsafe auto-restart.
When the overload interrupting device operates on a high-voltage motor circuit, what is required?
Correct: B — All ungrounded conductors must be disconnected simultaneously
430.206(B)(3) requires the overload interrupting device to simultaneously disconnect all ungrounded conductors, preventing single-phasing. Opening only one conductor, staggering the openings, or involving the neutral doesn't meet this requirement.
A motor of 1 hp or less that starts automatically needs overload protection by one of four permitted methods — separate device, integral thermal/electronic protector, failure-to-start protection, or sufficient winding impedance.
Which of the following is NOT one of the permitted overload protection methods for an automatically started motor of 1 hp or less under 430.32(B)?
Correct: C — Sizing the branch-circuit short-circuit protective device at 250% of full-load current
430.32(B) lists exactly four methods: a separate overload device, a thermal protector or electronic protection, a device integral with the motor protecting against failure-to-start damage, and impedance protection. Branch-circuit short-circuit protection sizing is a separate topic (430 Part IV) and is not one of the four overload options here.
Branch-circuit conductors for a single continuous-duty motor need an ampacity of at least 125% of the motor's full-load current rating from 430.6(A)(1).
A single motor operates in a continuous duty application. Per 430.22, what minimum ampacity must its branch-circuit conductors have?
Correct: A — 125% of the motor full-load current rating
430.22 requires conductors supplying a single continuous-duty motor to have an ampacity of not less than 125% of the motor full-load current rating from 430.6(A)(1). Sizing at 100% ignores the required margin, and the service-factor and 80% figures aren't the basis this rule uses.
A tap to one motor in a group installation skips its own branch-circuit protection only if the tap's length and ampacity fit one of 430.53(D)'s two size-for-length trade-offs.
A tap conductor runs from a group installation's branch circuit directly to a single motor's overload device, 22 ft away, with no individual branch-circuit protective device. Which condition must it meet under 430.53(D)(1)?
Correct: A — Ampacity not less than one-third the branch-circuit conductor ampacity
430.53(D)(1) allows the tap to be sized at not less than one-third the branch-circuit conductor ampacity (never below 430.22) as long as it's 25 ft or less and physically protected. The one-tenth ampacity option and the 10 ft length belong to the separate 430.53(D)(2) path for taps ending at a listed manual controller or protective device. Requiring full branch-circuit ampacity would defeat the point of the tap exception.
Motor conductors default to a 14 AWG minimum, but 18 AWG and 16 AWG copper are allowed for small motors when overload class and overcurrent protection meet strict amperage-tied conditions.
A technician is installing 18 AWG copper conductors inside a control cabinet to supply a 4-amp full-load-current motor, protected per 430.52 with Class 10 overload protection. Which section permits using conductors smaller than 14 AWG for this small motor circuit?
Correct: A — 430.22(G)(1)
430.22(G)(1) specifically permits 18 AWG copper conductors for motors with FLC greater than 3.5A up to 5A under the listed protection conditions. 430.22(G)(2) covers 16 AWG conductors for a different FLC range (5.5-8A), and 430.22(F) applies only to conductors between a stationary motor and a separate terminal enclosure, not general small-motor branch circuits.
One branch-circuit protective device can serve several motors only if it's sized to 430.52 for the smallest motor, each motor has its own overload protection, and it won't nuisance-trip under normal service.
Per 430.53(B), when two or more motors are supplied by a single branch-circuit short-circuit and ground-fault protective device, that device must be sized based on which motor?
Correct: B — The smallest rated motor in the group
430.53(B)(1) requires the shared protective device to be selected not to exceed what 430.52 allows for the smallest rated motor supplied by the circuit — sizing to the largest motor or an average current would let the device pass fault current too large to protect the smaller motor's conductors.
Separately excited dc motors, series motors, and converters that can overspeed from the dc end need a speed-limiting device unless inherent design or a qualified operator already limits speed.
Per 430.89, which of the following machines is required to have a speed-limiting device or other speed-limiting means?
Correct: B — A series motor
430.89 lists separately excited dc motors, series motors, and motor-generators/converters that can overspeed from the dc end as requiring speed-limiting means. A series motor is explicitly named. The other machine types listed are not among the three categories 430.89 addresses.
Line-side conductors are always sized at 125% of motor full-load current; motor-side conductors get a reduced percentage because they only carry part of the winding current.
Which statement correctly describes conductor sizing for a wye-start, delta-run connected motor?
Correct: B — Line-side conductors are sized at 125% of full-load current; motor-side conductors are sized at 72%
Per 430.22(C), branch-circuit conductors on the line side of the controller must have an ampacity of at least 125% of motor full-load current, while conductors between the controller and motor need only 72% because they carry just the 58% winding current (58% × 1.25 = 72%). Sizing both sides the same at 125%, swapping which side gets which percentage, or using the raw 58% figure instead of the adjusted 72% are all incorrect readings of the rule.
Article 430 is the master article for motors — conductors, protection, overload, control circuits, controllers, and control centers — but special equipment sends you elsewhere.
An electrician is sizing conductors and overload protection for a rooftop air-conditioning unit's compressor motor. Which article applies instead of Article 430?
Correct: D — Article 440
Per 430.1, air-conditioning and refrigerating equipment is directed to Article 440, not the general motor article. Part X of 430 covers adjustable-speed drives and Part XI covers motors over 1000 volts nominal — neither applies just because the load is a compressor motor.
With a bypass device, size the drive's supply conductors at 125% of the larger of the drive's rated input current or the motor's full-load current.
An adjustable-speed drive system includes a bypass device. Per 430.122(C), how must the supply conductor ampacity be determined?
Correct: A — The larger of 125% of the drive's rated input current or 125% of the motor full-load current
430.122(C) requires comparing 125% of the drive's rated input current with 125% of the motor full-load current (per 430.6) and using whichever is larger. Using only the drive's input current ignores the bypass path, summing the two overstates the load, and using 100% of FLC skips the required 125% factor.
A motor always needs overload protection — the drive can provide it, but a bypass circuit or multi-motor setup needs its own Part III protection.
A rooftop AHU is fed by an adjustable-speed drive whose nameplate states that motor overload protection is built into the power conversion equipment. The installer wants to confirm whether a separate overload relay must still be installed ahead of the motor. Which section governs whether additional overload protection is required in this case?
Correct: C — 430.124(A)
430.124(A) directly addresses power conversion equipment marked as including motor overload protection, waiving the need for a separate device. 430.126(A) instead covers overtemperature protection (a different protective function), and 430.124(C) applies only to multiple-motor installations, not this single marked-drive scenario.
Overload devices can't auto-restart a motor if that restart could hurt someone, but they can trip an alarm instead of an instant shutdown when stopping the motor is the more dangerous option.
A facility wants to install a motor overload device that automatically restarts the motor after it trips on overload. Under 430.43, when is this NOT permitted?
Correct: A — When automatic restarting of the motor could result in injury to persons
430.43 prohibits an automatic-restarting overload device whenever restarting the motor could injure a person, regardless of approval status otherwise. Approval for use with the motor is a separate, necessary condition, not itself a bar to installation. Continuous-process operation and alarm connections relate to 430.44's orderly-shutdown alternative, not the restart prohibition in 430.43.
An autotransformer starter must have off, running, and starting positions, and it can't rest anywhere that bypasses overload protection.
According to 430.82(B), which positions must an autotransformer starter provide?
Correct: A — Off, running, and at least one starting position
430.82(B) requires an autotransformer starter to have an off position, a running position, and at least one starting position. Options that drop the starting position or the off position don't meet this three-position requirement.
A manufacturer's overload relay table or equipment marking is a hard ceiling on branch-circuit short-circuit and ground-fault protection — it wins even when 430.52's percentage tables allow a bigger device.
A motor controller's overload relay table specifies a maximum branch-circuit short-circuit and ground-fault protective device rating that is lower than the value permitted by the standard percentage-of-full-load-current table. What is the electrician required to do?
Correct: C — Not exceed the rating shown in the overload relay table
Per 430.52(C)(2), where a maximum protective device rating is shown in a manufacturer's overload relay table or otherwise marked on the equipment, that value shall not be exceeded even if the percentage-based tables would allow a higher rating. Using the percentage table value, a higher value, or an averaged value all ignore the marked limit.
Part IV devices protect motor branch-circuit conductors, controllers, and motors against short circuits and ground faults only — not against overload, and not above 1000 volts.
A single 10 hp, 480V, three-phase motor's branch circuit needs short-circuit and ground-fault protection sized before the motor is even installed. Which section covers the general scope of the devices used for this protection under Part IV of Article 430?
Correct: C — 430.51
430.51 states the purpose of Part IV — protecting motor branch-circuit conductors, control apparatus, and motors against short circuits and ground faults — and notably excludes GFCI/GFPE devices under 210.8, 230.95, and 590.6. 430.52 covers actual rating/setting calculations, not the scope statement, so it's the closer but wrong distractor.
An ampere-rated inverse time circuit breaker or a molded case switch can serve as the motor controller for any motor — no horsepower rating needed.
A 5 hp, 480V three-phase motor branch circuit uses an inverse time circuit breaker as the motor controller, and that same breaker is also being relied on to provide the motor's overload protection. Which section requires this dual-use breaker to also meet the article's overload-protection provisions?
Correct: B — 430.83(A)(2)
430.83(A)(2) permits an inverse time circuit breaker as a controller for all motors, and specifically states that when it doubles as overload protection it must meet the article's overload provisions. 430.83(A)(3) covers molded case switches, not breakers, and 430.82 governs general controller design (starting/stopping duty), not the breaker-as-overload-device rule.
AC adjustable-voltage drive motors size conductors from the nameplate max operating current (or 150% of Table 430.249/430.250 if none is marked); valve actuator motor assemblies always size from nameplate full-load current.
An AC adjustable voltage, variable torque drive motor has a maximum operating current clearly marked on its control nameplate. How should conductor ampacity be determined per 430.6(C)?
Correct: A — Use the marked maximum operating current from the nameplate
Per 430.6(C), when the maximum operating current is marked on the motor or control nameplate, that value governs conductor ampacity. The 150 percent of Table 430.249/430.250 method is only a fallback used when no such marking exists, and the full-load-current method belongs to valve actuator motor assemblies under 430.6(D), not adjustable-voltage drives.
A motor controller can double as the overload device only if it has the right number of overload units per Table 430.37 and they're active in running position (and starting position too, for DC motors).
A 5 hp, 480V ac motor on continuous duty has separate overload relays sized per Table 430.37, but the electrician wants to skip a dedicated overload relay and instead use the motor controller itself as the overload device. Which section permits this and sets the condition that the overload units be operative in the running position for an ac motor?
Correct: B — 430.39
430.39 specifically allows a motor controller to double as the overload device, conditioned on the number of overload units matching Table 430.37 and being operative in the running position (ac) or starting and running (dc). 430.40 covers overload relay ratings/settings, not using the controller itself as the device, and 430.38 addresses how many conductors an overload device must open, not the controller-as-overload permission.
A motor controller only has to switch enough conductors to start and stop the motor — it must open all ungrounded conductors only when it's also doing disconnect duty.
A 15 hp, 480V three-phase motor has its controller mounted separately from a disconnecting means that is located within sight of the motor. An inspector asks whether the controller itself is required to open every ungrounded conductor to the motor. Which section answers whether the controller must open all conductors?
Correct: B — 430.84
430.84 states the motor controller is not required to open all conductors to the motor, unless it also serves as the disconnecting means. 430.75 governs disconnection of control circuits, not the controller's conductor-opening duty, and 430.87 addresses how many motors one controller may serve — neither answers this question.
A motor controller's horsepower rating at the application voltage must be at least equal to the motor's horsepower rating.
An electrician is selecting a manual motor starter (not an inverse time circuit breaker or molded case switch) to control a 10 HP, 480V three-phase motor. Which section specifies the minimum horsepower rating the controller must have?
Correct: D — 430.83(A)(1)
430.83(A)(1) requires motor controllers (other than inverse time circuit breakers and molded case switches) to carry a horsepower rating at the application voltage not lower than the motor's horsepower. 430.83(A)(2) instead addresses circuit breakers used as controllers, and 430.81(A) covers general-use switches for stationary motors of 1/8 HP or less, neither of which sets this rating requirement.
Never install a motor controller where available fault current exceeds its short-circuit current rating (SCCR).
Per 430.83(F), what determines whether a motor controller is permitted at a given location?
Correct: C — The available fault current at that location must not exceed the controller's short-circuit current rating
430.83(F) prohibits installing a motor controller where available fault current exceeds its short-circuit current rating (SCCR). Horsepower matching, the 125% full-load current factor, and sight-disconnect rules are real 430 requirements but are governed by other subsections, not the SCCR limit in 430.83(F).
A straight-rated controller just needs a rating ≥ the circuit's line-to-line voltage; a slash-rated controller needs the circuit solidly grounded, with both its line-to-ground and line-to-line voltages fitting the two label values.
A shop is wiring a motor controller that will be installed on an ungrounded 480-volt, 3-phase delta system where no conductor is referenced to ground. The controller nameplate shows a single voltage rating rather than two values separated by a slash. Which section governs whether this straight-rated controller may be applied on this circuit?
Correct: B — 430.83(E)
430.83(E) is the Voltage Rating provision distinguishing straight-rated controllers (permitted if nominal voltage between any two conductors doesn't exceed the rating) from slash-rated controllers (which require a solidly grounded system). 430.83(A) covers General ratings tied to horsepower/breaker/switch selection, not voltage rating rules, so it doesn't answer this scenario.
Conductors to separately mounted power accelerating and dynamic braking resistors are sized from Table 430.29 using motor full-load current, not the ampacity tables you'd use for regular branch-circuit conductors.
A DC motor controller connects to a separately mounted dynamic braking resistor. Per 430.29, what value is the starting point for sizing the connecting conductors using Table 430.29?
Correct: B — The motor's full-load current
430.29 states that conductors connecting the motor controller to separately mounted power accelerating and dynamic braking resistors must have an ampacity not less than the value calculated from Table 430.29 using motor full-load current. The resistor wattage-based figure, the horsepower-to-amperes conversion, and the protective device rating are not the basis this section specifies.
Size the rectifier's input conductors at 125% of rated input current, then size the DC output conductors at 150% or 190% of motor full-load current depending on bridge type.
A DC motor is supplied through a single-phase, full-wave rectifier bridge. Per 430.22(A), how must the conductors between the rectifier's output terminals and the motor be sized?
Correct: D — Not less than 150% of the motor full-load current rating
430.22(A) requires output conductors on a full-wave rectifier-supplied DC motor to have an ampacity of at least 150% of motor full-load current. The 190% figure applies only to half-wave bridges, and the 125% figures describe the input side of the rectifier, not the motor-side output conductors.
A dedicated controller isn't always required — small motors can use the branch-circuit disconnect (≤18 hp, stationary) or a plug/cord connector (≤13 hp, portable) instead.
A stationary clock motor rated at 1/12 hp runs continuously and cannot be damaged by overload or failure to start. What can serve as its motor controller?
Correct: D — The branch-circuit disconnecting means
Per 430.81(A), a stationary motor of 1/8 hp or less that is normally left running and cannot be damaged by overload or failure to start may use the branch-circuit disconnecting means as its controller. The plug/receptacle and cord connector options apply to portable motors under 430.81(B), not stationary ones.
When a feeder serves motors plus other loads, size the protective device for the other loads' full rating plus the largest allowed motor-branch-circuit protection value.
A feeder supplies one 25 hp, 460V, 3-phase motor plus a 30A continuous non-motor load such as lighting. Which section establishes the required rating of the feeder overcurrent protective device by combining the motor's branch-circuit rating with the other load?
Correct: A — 430.63
430.63 covers feeders supplying a motor load plus other (non-motor) load(s), setting the device rating at the sum of the other load(s) plus the motor's permitted rating per 430.52/430.62. 430.62 only addresses feeders serving motor loads alone, with no other load added in.
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