CSLB Trade — Electrical (C-10) — All Questions

A motor nameplate reads 28 A full-load, service factor 1.0, temperature rise not marked. What is the maximum overload rating under NEC 430.32(A)(1)?

• a.35 A
• b.28 A
• c.30.8 A
• d.32.2 A✓

Motors without a 1.15+ service factor or a 40C-or-less marked temperature rise are limited to 115% of nameplate FLA: 28 x 1.15 = 32.2 A. 125% (35 A) applies only to SF >=1.15 or <=40C-rise motors, and 30.8 A is 110%.2023 NEC §430.32

A feeder supplies two three-phase, 460 V motors: 20 HP (FLC 27 A) and 10 HP (FLC 14 A). Per NEC 430.24, what minimum feeder conductor ampacity is required?

• a.41 A
• b.47.75 A✓
• c.54 A
• d.51.25 A

NEC 430.24 requires 125% of the largest motor's FLC plus the sum of the others: (27 x 1.25) + 14 = 33.75 + 14 = 47.75 A. 41 A omits the 125% factor, 51.25 A applies 125% to both, and 54 A doubles the largest.2023 NEC §430.24

A motor disconnecting means must have an ampere rating at least 115% of the motor FLC. For a 15 HP, 460 V, three-phase motor (FLC 21 A), what is the minimum disconnect ampere rating?

• a.18.9 A
• b.21 A
• c.26.25 A
• d.24.15 A✓

NEC 430.110(A) requires the disconnecting means to be rated at least 115% of the FLC: 21 x 1.15 = 24.15 A. 21 A ignores the 115% factor, 26.25 A is 125%, and 18.9 A is 90%.2023 NEC §430.110

In a motor installation, what is the primary function of the motor controller?

• a.To protect conductors from overload only
• b.To provide short-circuit and ground-fault protection
• c.To start and stop the motor by connecting and disconnecting it from the power source✓
• d.To serve as the required disconnecting means for maintenance

NEC Article 430 Part VII defines the controller as the device that starts and stops the motor by making and breaking the motor-circuit current. Short-circuit protection, overload protection, and the disconnecting means are separate required elements, though one device can sometimes serve more than one role.2023 NEC §430.81

A motor control circuit tapped from the load side of the motor branch-circuit protection is generally protected against overcurrent according to which NEC provision?

• a.NEC 430.72 (motor control circuits)✓
• b.Table 430.52
• c.Article 240 only
• d.Article 450

NEC 430.72 and Table 430.72(B) govern overcurrent protection of motor control circuit conductors, including tapped control conductors. Table 430.52 covers motor branch-circuit (power) protection, Article 240 covers general circuits, and Article 450 covers transformers.2023 NEC §430.72

A single hermetic refrigerant motor-compressor has a rated-load current of 24 A. Per NEC 440.32, what minimum branch-circuit conductor ampacity is required?

• a.28.8 A
• b.24 A
• c.26 A
• d.30 A✓

NEC 440.32 requires conductors for a single motor-compressor to be sized at 125% of the rated-load current or branch-circuit selection current, whichever is larger: 24 x 1.25 = 30 A. 24 A omits the factor, 26 A is ~108%, and 28.8 A is 120%.2023 NEC §440.32

On an air-conditioning unit nameplate, what does the 'Minimum Circuit Ampacity (MCA)' value tell the installer?

• a.The minimum ampacity the branch-circuit conductors must have✓
• b.The locked-rotor current of the compressor
• c.The maximum fuse or breaker size allowed
• d.The full-load current of the condenser fan only

MCA is the minimum conductor ampacity required to supply the unit, already calculated by the manufacturer (125% of the largest motor plus other loads). The maximum overcurrent device is the separate MOCP/'Max Fuse' value; MCA is not a fan rating or locked-rotor value.2023 NEC §440.4

The 'Maximum Overcurrent Protective Device' (MOCP or 'Max Fuse/HACR Breaker') rating on an HVAC nameplate specifies what?

• a.The disconnect switch rating only
• b.The smallest breaker that will start the unit
• c.The required conductor size
• d.The largest fuse or circuit breaker permitted to protect the branch circuit✓

The MOCP is the maximum size of fuse or HACR-rated breaker allowed for the unit's branch circuit; you may install this size or smaller, but not larger. MCA sets the conductor ampacity; the two values are used together per 440.4(B).2023 NEC §440.4

An A/C condensing unit has a compressor rated-load current of 18 A and a fan motor of 2 A. Using the 125%-of-largest-motor-plus-others method, what is the minimum circuit ampacity (MCA)?

• a.25 A
• b.27.5 A
• c.24.5 A✓
• d.20 A

MCA = 125% of the largest motor + sum of the other loads: (18 x 1.25) + 2 = 22.5 + 2 = 24.5 A. 20 A omits the 125% factor, 25 A applies 125% to the whole 20 A, and 27.5 A applies 125% to both loads.2023 NEC §440.33

For a hermetic motor-compressor with a rated-load current of 18 A, what is the maximum branch-circuit short-circuit/ground-fault protective device, based on the 175% value of NEC 440.22(A)?

• a.31.5 A✓
• b.40.5 A
• c.22.5 A
• d.27 A

NEC 440.22(A) sizes the protective device at not more than 175% of the rated-load (or branch-circuit selection) current: 18 x 1.75 = 31.5 A. 22.5 A is 125% (conductor factor), 27 A is 150%, and 40.5 A is 225% (the absolute maximum only where needed to start).2023 NEC §440.22

If a motor-compressor (rated-load 18 A) will not start on the 175% device, NEC 440.22(A) permits increasing the protection to a maximum of what value?

• a.300% = 54 A
• b.250% = 45 A
• c.225% = 40.5 A✓
• d.200% = 36 A

NEC 440.22(A) allows an increase up to 225% of the rated-load current where the 175% device will not carry starting current: 18 x 2.25 = 40.5 A. 200%, 250%, and 300% are not the permitted ceilings for hermetic-compressor branch-circuit protection.2023 NEC §440.22

A 30 kVA, three-phase transformer has a 480 V primary (primary current ~36 A). With primary-only protection and no supervised condition, what is the maximum primary overcurrent device using the 125% factor of Table 450.3(B)?

• a.45 A✓
• b.60 A
• c.36 A
• d.72 A

For a transformer with primary current of 9 A or more, Table 450.3(B) limits primary-only protection to 125%: 36 x 1.25 = 45 A (with the note allowing the next standard size where 125% does not correspond). 36 A omits the factor, 60 A is ~167%, and 72 A is 200%.2023 NEC §450.3

NEC 450.3(B) overcurrent protection percentages for transformers 1000 V or less are based on what?

• a.The available fault current
• b.The connected load kVA
• c.The secondary conductor ampacity
• d.The rated primary (and where applicable secondary) current of the transformer✓

Table 450.3(B) percentages (e.g., 125%, 167%, 250%, 300%) are applied to the transformer's rated primary or secondary current, not the load or fault current. This protects the transformer itself; separate rules protect the secondary conductors.2023 NEC §450.3

What is the rated primary current of a 25 kVA, single-phase transformer with a 240 V primary?

• a.60 A
• b.96 A
• c.104 A✓
• d.83 A

For a single-phase transformer, I = VA / V = 25,000 / 240 = 104 A. Using 208 V would give 120 A, 300 V gives 83 A, and 416 V gives 60 A; only the correct 240 V yields about 104 A.

A 45 kVA, three-phase transformer has a 208 V secondary. What is the rated secondary current?

• a.108 A
• b.150 A
• c.216 A
• d.125 A✓

For three-phase, I = VA / (1.732 x V) = 45,000 / (1.732 x 208) = 45,000 / 360 = about 125 A. Dividing by 208 alone (216 A) ignores the sqrt(3) factor, and the other values use wrong voltages.

Why must a motor circuit have both overload protection AND short-circuit/ground-fault protection?

• a.Overload devices protect against sustained overcurrents from motor running conditions, while short-circuit/ground-fault devices clear high-magnitude faults✓
• b.Overloads clear faults faster than breakers
• c.They are the same device required in two locations
• d.Short-circuit devices also sense motor running overload

Overload devices (sized ~115-125% of FLA) protect the motor and conductors from sustained overloads but are too slow for faults; branch-circuit short-circuit/ground-fault devices (sized much higher per Table 430.52) clear high fault currents. NEC 430 requires both because each addresses a different hazard.2023 NEC §430.31

A 30 HP, 460 V, three-phase motor has an FLC of 40 A. What is the minimum ampere rating of the motor disconnecting means (115% of FLC)?

• a.44 A
• b.46 A✓
• c.50 A
• d.40 A

NEC 430.110(A) requires the disconnect to be at least 115% of FLC: 40 x 1.15 = 46 A. 40 A ignores the factor, 44 A is 110%, and 50 A is 125% (used for conductors, not the minimum disconnect).2023 NEC §430.110

Under NEC 430.102(B), where must the disconnecting means for a motor generally be located?

• a.In sight from the motor location and the driven machinery✓
• b.At least 50 ft from the motor
• c.At the service equipment only
• d.Anywhere in the building

NEC 430.102(B) requires a disconnecting means in sight from the motor and the driven machinery (with limited exceptions where a lockable disconnect elsewhere is permitted). 'In sight' means visible and not more than 50 ft away. Service-only or remote-only placement does not satisfy the rule.2023 NEC §430.102

Per NEC Table 430.248, what is the full-load current of a 3 HP, single-phase, 115 V motor?

• a.34 A✓
• b.56 A
• c.17 A
• d.24 A

Table 430.248 lists 34 A for a 3 HP, 115 V single-phase motor. 17 A is the same HP at 230 V, 24 A is a 2 HP 115 V motor, and 56 A is a 5 HP 115 V motor.2023 NEC Table 430.248

For the 3 HP, 115 V single-phase motor (FLC 34 A), what minimum branch-circuit conductor ampacity does NEC 430.22 require?

• a.46.75 A
• b.34 A
• c.38.25 A
• d.42.5 A✓

NEC 430.22 requires 125% of FLC for a single continuous-duty motor: 34 x 1.25 = 42.5 A. 34 A omits the factor, 38.25 A uses 112.5%, and 46.75 A uses 137.5%.2023 NEC §430.22

Using NEC Table 430.250, what is the full-load current of a 50 HP, 460 V, three-phase motor?

• a.77 A
• b.65 A✓
• c.96 A
• d.52 A

Table 430.250 lists 65 A for a 50 HP, 460 V three-phase motor. 52 A is 40 HP, 77 A is 60 HP, and 96 A is 75 HP at 460 V.2023 NEC Table 430.250

For the 50 HP, 460 V motor (FLC 65 A), what minimum branch-circuit conductor ampacity is required by NEC 430.22?

• a.81.25 A✓
• b.71.5 A
• c.74.75 A
• d.65 A

430.22 requires 125% of FLC: 65 x 1.25 = 81.25 A. 65 A omits the factor, 71.5 A is 110%, and 74.75 A is 115%.2023 NEC §430.22

For the 50 HP, 460 V motor (FLC 65 A), what is the maximum inverse-time circuit breaker per the 250% column of Table 430.52?

• a.195 A
• b.113.75 A
• c.520 A
• d.162.5 A✓

Inverse-time breaker: 250% of FLC = 65 x 2.50 = 162.5 A (then next-standard-size rule may apply). 113.75 A is 175% (dual-element fuse), 195 A is 300% (nontime-delay fuse), and 520 A is 800% (instantaneous trip).2023 NEC §430.52

For a continuous-duty three-phase motor rated more than 1 HP without integral overload protection, how many overload units are generally required?

• a.Two units for any motor
• b.None if a breaker is used
• c.One overload unit total
• d.One overload unit in each phase (three for a three-phase motor)✓

NEC 430.37 and Table 430.37 require an overload device in each ungrounded conductor - three units for a three-phase motor - so a loss of one phase or unbalanced overload is detected. A single unit is insufficient, and a branch-circuit breaker does not provide running overload protection.2023 NEC §430.37

A continuous-duty motor has a nameplate FLA of 62 A and a service factor of 1.15. What is the maximum overload device rating at 125% under NEC 430.32(A)(1)?

• a.71.3 A
• b.62 A
• c.86.8 A
• d.77.5 A✓

125% of nameplate FLA for an SF >=1.15 motor: 62 x 1.25 = 77.5 A. 62 A omits the factor, 71.3 A is 115%, and 86.8 A is 140% (the higher trip ceiling of 430.32(C), used only when the 125% device won't allow starting).2023 NEC §430.32

If the 125% overload device will not allow a 62 A (SF 1.15) motor to start, NEC 430.32(C) permits increasing the overload trip setting to a maximum of what value?

• a.86.8 A (140%)✓
• b.80.6 A (130%)
• c.77.5 A (125%)
• d.83.7 A (135%)

NEC 430.32(C) allows the overload trip to be increased to a maximum of 140% of nameplate FLA (for SF >=1.15 motors) when the sized device won't let the motor start: 62 x 1.40 = 86.8 A. 130% and 135% are not the code ceiling, and 125% is the initial value.2023 NEC §430.32

Per NEC Table 430.248, what is the full-load current of a 2 HP, single-phase, 230 V motor?

• a.17 A
• b.10 A
• c.12 A✓
• d.24 A

Table 430.248 lists 12 A for a 2 HP, 230 V single-phase motor. 24 A is the same HP at 115 V, 10 A is a 1.5 HP 230 V motor, and 17 A is a 3 HP 230 V motor.2023 NEC Table 430.248

Using NEC Table 430.250, what is the full-load current of a 100 HP, 460 V, three-phase motor?

• a.124 A✓
• b.248 A
• c.156 A
• d.96 A

Table 430.250 lists 124 A for a 100 HP, 460 V three-phase motor. 156 A is 125 HP, 96 A is 75 HP, and 248 A is a 100 HP motor at 230 V.2023 NEC Table 430.250

For a 100 HP, 460 V motor (FLC 124 A), what minimum branch-circuit conductor ampacity does NEC 430.22 require?

• a.174.6 A
• b.136.4 A
• c.124 A
• d.155 A✓

430.22 requires 125% of FLC: 124 x 1.25 = 155 A. 124 A omits the factor, 136.4 A is 110%, and 174.6 A is about 141%.2023 NEC §430.22

For the 100 HP, 460 V motor (FLC 124 A), what is the maximum dual-element (time-delay) fuse per Table 430.52 (175%)?

• a.217 A✓
• b.310 A
• c.155 A
• d.372 A

Dual-element time-delay fuse: 175% of FLC = 124 x 1.75 = 217 A. 310 A is 250% (inverse-time breaker), 372 A is 300% (nontime-delay fuse), and 155 A is 125% (conductor factor).2023 NEC §430.52

In a typical motor branch circuit, which sequence correctly lists the components from the supply toward the motor?

• a.Motor, overload, controller, disconnect, fuse
• b.Overload, motor, controller, disconnect
• c.Controller, motor, fuse, disconnect
• d.Branch-circuit short-circuit/ground-fault device, disconnecting means, controller, overload device, motor✓

Article 430 arranges the motor circuit as: branch-circuit short-circuit/ground-fault protection, then the disconnecting means, then the controller, then the overload device, then the motor. The other sequences misplace the protective and control elements.2023 NEC §430.1

An HVAC nameplate lists MCA = 27.5 A and MOCP = 45 A. What is the minimum ampacity the branch-circuit conductors must have?

• a.45 A
• b.22 A
• c.35 A
• d.27.5 A✓

Conductors must have an ampacity at least equal to the MCA (27.5 A); the MOCP (45 A) is the maximum overcurrent device, not the conductor ampacity. Sizing conductors to 45 A would be oversized/incorrect, and 22 A is below the required MCA.2023 NEC §440.4

A rooftop A/C unit has one compressor at 30 A rated-load and a condenser fan at 1.5 A. What is the minimum circuit ampacity (MCA), using 125% of the largest motor plus other loads?

• a.40.5 A
• b.31.5 A
• c.39 A✓
• d.37.5 A

MCA = (30 x 1.25) + 1.5 = 37.5 + 1.5 = 39 A. 37.5 A forgets the fan, 31.5 A applies 125% to a wrong base, and 40.5 A applies 125% to both loads.2023 NEC §440.33

An HVAC nameplate specifies 'Maximum Fuse or HACR Breaker.' What does HACR indicate?

• a.The breaker must be a GFCI type
• b.The circuit breaker is rated/listed for heating, air-conditioning, and refrigeration group-motor applications✓
• c.The breaker must be rated for 100% continuous duty
• d.Only fuses may be used, not breakers

HACR-rated breakers are listed for heating, air-conditioning, and refrigeration equipment with group motor-compressor loads. The nameplate permits either a fuse or an HACR breaker up to the marked value; it does not mandate GFCI or fuses-only.2023 NEC §440.22

What is the rated secondary current of a 75 kVA, three-phase transformer with a 208 V secondary?

• a.360 A
• b.208 A✓
• c.125 A
• d.180 A

Three-phase current: I = 75,000 / (1.732 x 208) = 75,000 / 360 = about 208 A. Dividing by 208 V alone (360 A) omits sqrt(3), and the other values use wrong kVA or voltage.

For the 75 kVA transformer with a 208 A secondary, what is the maximum secondary overcurrent protective device using the 125% value of Table 450.3(B)?

• a.260 A✓
• b.208 A
• c.416 A
• d.347 A

Table 450.3(B) allows secondary protection at 125% of rated secondary current (currents >=9 A): 208 x 1.25 = 260 A. 208 A omits the factor, 347 A is about 167%, and 416 A is 200%.2023 NEC §450.3

NEC 450.9 requires that transformer ventilation openings be arranged so that they:

• a.Are always fitted with fans
• b.Are sealed to keep out dust
• c.Are not blocked by walls or obstructions, allowing required airflow to dissipate heat✓
• d.Face downward only

NEC 450.9 requires ventilation so transformers can dissipate full-load losses without exceeding temperature ratings; openings must not be blocked by walls or obstructions. Forced ventilation is not always required, and sealing openings would defeat cooling.2023 NEC §450.9

A feeder supplies three 460 V, three-phase motors: 25 HP (34 A), 15 HP (21 A), and 10 HP (14 A). Per NEC 430.24, what minimum feeder ampacity is required?

• a.84 A
• b.69 A
• c.77.5 A✓
• d.86.25 A

430.24 requires 125% of the largest FLC plus the sum of the rest: (34 x 1.25) + 21 + 14 = 42.5 + 35 = 77.5 A. 69 A omits the 125% factor, 86.25 A applies 125% to all, and 84 A doubles wrongly.2023 NEC §430.24

Per NEC 430.62, the maximum feeder overcurrent device for several motors equals the largest branch-circuit protective device rating plus the sum of the other motors' FLCs. If the largest motor's branch device is 90 A and the other motors' FLCs total 35 A, what is the maximum feeder device?

• a.125 A✓
• b.160 A
• c.215 A
• d.90 A

430.62(A): 90 A (largest branch device) + 35 A (sum of other FLCs) = 125 A maximum. 215 A wrongly adds all device ratings, 90 A ignores the other motors, and 160 A uses the wrong sum.2023 NEC §430.62

The equipment grounding conductor for a motor branch circuit is sized based on what, per NEC 250.122?

• a.The motor horsepower
• b.The conductor insulation temperature
• c.The rating of the branch-circuit short-circuit/ground-fault protective device✓
• d.The full-load current only

NEC 250.122 sizes the equipment grounding conductor from Table 250.122 using the rating of the overcurrent device (the branch-circuit short-circuit/ground-fault device) ahead of the equipment. Horsepower, FLC alone, and insulation rating do not directly set the EGC size.2023 NEC §250.122

Per NEC Table 430.250, what is the full-load current of a 7.5 HP, 230 V, three-phase motor?

• a.11 A
• b.15.2 A
• c.22 A✓
• d.28 A

Table 430.250 lists 22 A for a 7.5 HP, 230 V three-phase motor. 15.2 A is 5 HP, 28 A is 10 HP at 230 V, and 11 A is 7.5 HP at 460 V.2023 NEC Table 430.250

For the 7.5 HP, 230 V motor (FLC 22 A), what minimum branch-circuit conductor ampacity is required by NEC 430.22?

• a.22 A
• b.25.3 A
• c.27.5 A✓
• d.24.2 A

125% of FLC: 22 x 1.25 = 27.5 A. 22 A omits the factor, 24.2 A is 110%, and 25.3 A is 115%.2023 NEC §430.22

For the 7.5 HP, 230 V motor (FLC 22 A), what is the maximum nontime-delay fuse per Table 430.52 (300%)?

• a.38.5 A
• b.55 A
• c.66 A✓
• d.176 A

Nontime-delay fuse: 300% of FLC = 22 x 3.00 = 66 A. 55 A is 250% (inverse-time breaker), 38.5 A is 175% (dual-element fuse), and 176 A is 800% (instantaneous trip).2023 NEC §430.52

When the Table 430.52 percentage produces a value that does not correspond to a standard fuse or breaker size, NEC 430.52(C)(1) Exception No. 1 permits you to:

• a.Ignore the table and use conductor ampacity
• b.Round down to the next lower standard size
• c.Double the value
• d.Use the next higher standard size of protective device✓

430.52(C)(1) Exception No. 1 allows using the next higher standard size when the calculated maximum does not match a standard rating, so the motor can start. Rounding down could cause nuisance tripping; doubling or ignoring the table is not permitted.2023 NEC §430.52

Per NEC Table 430.248, what is the full-load current of a 1 HP, single-phase, 115 V motor?

• a.16 A✓
• b.9.8 A
• c.20 A
• d.13.8 A

Table 430.248 lists 16 A for a 1 HP, 115 V single-phase motor. 9.8 A is 1/2 HP, 13.8 A is 3/4 HP, and 20 A is 1.5 HP at 115 V.2023 NEC Table 430.248

A small single-phase motor has a nameplate FLA of 14 A, service factor 1.0, no marked temperature rise. What is the maximum overload device rating under NEC 430.32(A)(1)?

• a.14 A
• b.17.5 A
• c.16.1 A✓
• d.15.4 A

Without a 1.15+ SF or <=40C rise marking, overload is limited to 115% of nameplate: 14 x 1.15 = 16.1 A. 125% (17.5 A) applies only to qualifying motors, 15.4 A is 110%, and 14 A applies no factor.2023 NEC §430.32

NEC 430.75 requires that motor control circuits be arranged so that:

• a.Control circuits need no overcurrent protection
• b.Control circuits are always 24 V
• c.The control circuit is disconnected from all sources of supply when the disconnecting means is open✓
• d.Control conductors are the same size as power conductors

NEC 430.75 requires the disconnecting means to open the motor control circuit from all sources when placed in the off position (with limited exceptions), so a technician is not exposed to energized controls. Control voltage level, conductor size parity, and 'no protection' are not the rule.2023 NEC §430.75

A 15 kVA, single-phase transformer has a 480 V primary. What is the rated primary current?

• a.36 A
• b.62.5 A
• c.72 A
• d.31.25 A✓

Single-phase: I = 15,000 / 480 = 31.25 A. Using 240 V would give 62.5 A, and the other values use incorrect voltages or the sqrt(3) factor that does not apply to single-phase.

For the 15 kVA, 480 V single-phase transformer (primary current 31.25 A), what is the maximum primary-only overcurrent device using the 125% factor of Table 450.3(B)?

• a.31.25 A
• b.39.1 A✓
• c.62.5 A
• d.46.9 A

Primary current >=9 A limits primary-only protection to 125%: 31.25 x 1.25 = 39.1 A (next standard size up permitted where needed). 31.25 A omits the factor, 46.9 A is 150%, and 62.5 A is 200%.2023 NEC §450.3

Which of the following is NOT required to be marked on a motor nameplate by NEC 430.7?

• a.Rated full-load amperes
• b.Rated frequency and number of phases
• c.The branch-circuit conductor size to be installed✓
• d.Rated voltage and horsepower (or kW)

NEC 430.7 requires the manufacturer, voltage, HP/kW, FLA, frequency, phases, speed, and similar data on the nameplate, but not the field branch-circuit conductor size - that is the installer's design calculation. All other listed items are required nameplate markings.2023 NEC §430.7