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MASTER NEC 2023

Master Electrician Practice Test 22 – Panelboards, Switchboards & Switches

This is Master Electrician Practice Test 22 — Panelboards, Switchboards & Switches, covering NEC Article 408 (panelboards and switchboards), the overcurrent device location rules in Article 240, and switch rules from Article 404. The test has 25 multiple-choice questions on panelboard overcurrent protection, circuit directories, back-fed breakers, where overcurrent devices may and may not be located, and switch ratings for general and motor loads. Pass score is 70%. Every question includes a full NEC 2023 explanation so you can trace each answer back to the exact code section.

TOPICS COVERED

Panelboards & Switches

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Frequently Asked Questions

Yes — completely free with no signup required. All answers include detailed explanations.

Requirements vary by state but typically include 4–8 years of documented electrical work experience plus a valid Journeyman license.

Advanced NEC code interpretation, load calculations, service entrance design, motor controls, generator systems, and electrical system design.

The Master exam focuses more on design, calculations, and planning rather than installation details. Load calculation and service sizing questions are weighted heavily.

Before You Start

25 questions — multiple choice
45 minutes to finish (timer starts when you begin)
Pass score is 70% — you need at least 18 correct answers
Full NEC 2023 explanation shown for every question after you submit

Topics in This Test

Maximum number of overcurrent devices — as designed, rated, and listed; no 42-device limit since 2008 (NEC 408.54)
Overcurrent protection for a panelboard cannot exceed the panelboard's own rating (NEC 408.36)
Grounded conductors must each land on their own terminal (NEC 408.41)
Back-fed breakers used as a main need an additional fastener (NEC 408.36(D))
Unused panelboard openings must be closed with identified closures (NEC 408.7)
Panelboard circuit directories must be specific and legible (NEC 408.4(A))
Feeder-supplied panelboard marking — source of supply (NEC 408.4(B))
Overcurrent devices not near easily ignitible material, like closets (NEC 240.24(D))
Overcurrent devices not permitted in bathrooms or shower rooms (NEC 240.24(E))
Overcurrent devices not permitted over stairway steps (NEC 240.24(F))
Maximum height for a breaker operating handle — 6 ft 7 in (NEC 240.24)
Switches and breakers must not disconnect the grounded conductor (NEC 404.2(B))
Grounded conductor required at switch locations for electronic switches (NEC 404.2(C))
Exception — a switch controlling only a receptacle load (NEC 404.2(C))
AC-DC general-use snap switch — inductive load limited to 50% of rating (NEC 404.14)
AC-DC snap switch for motor control — rated at least 2x motor FLC (NEC 404.14)
General-use AC snap switch permitted for small stationary motors (NEC 430.109)
Horsepower-rated switch generally required for motor disconnects (NEC 430.109)
Panelboards must be dead-front construction
Switchboard vs. panelboard — general distinction
High leg on the B phase (NEC 408.3(E)(1))
Interrupting rating vs. available fault current (NEC 110.9, 240.86)
Panelboards may not be installed face-up (NEC 408.43)
Airspace behind cabinets in damp locations — 1/4 in. (NEC 312.2)
Next-size-up OCPD for feeder conductors, checked against the panelboard rating (NEC 240.4(B), 408.36)

Tip: Most of Article 240's location rules exist to keep a breaker panel somewhere a person can actually reach it in a hurry, and away from water, fire hazards, and blind spots. If you understand the "why," the specific list of prohibited spots is easy to remember.

Questions

45 min

Time

70%

Pass

Timer starts immediately. Progress is auto-saved.

Master Electrician Practice Test 22 – Panelboards, Switchboards & Switches — Question List

Question 1: Under NEC 408.54, what is the maximum number of overcurrent devices permitted in a panelboard?

42, not counting the main
30, when more than 10% of the devices are rated 30 A or less
The number for which the panelboard is designed, rated, and listed
Unlimited, as long as there is room in the enclosure

NEC Reference: NEC 408.54

Question 2: NEC 408.36 requires the overcurrent device protecting a panelboard to have a rating:

Not greater than the panelboard's own rating
At least double the panelboard's rating
Exactly half the panelboard's rating
There is no relationship between the two ratings

NEC Reference: NEC 408.36

Question 3: NEC 408.41 requires each grounded (neutral) conductor terminating in a panelboard to:

Have its own individual terminal, not shared with another conductor
Share a terminal with the equipment grounding conductor
Share a terminal with any other neutral in the panel
Be left unterminated for future use

NEC Reference: NEC 408.41

Question 4: A plug-in circuit breaker is installed back-fed and used as the main disconnect for a panelboard (common in some solar interconnections). What does NEC 408.36(D) require?

An additional fastener that takes more than a simple pull to release
Nothing extra — a standard plug-in breaker is always sufficient
A second, redundant panelboard installed nearby
A prohibition on ever back-feeding any breaker

NEC Reference: NEC 408.36(D)

Question 5: A panelboard has two open breaker slots with no breakers installed. What does NEC 408.7 require for those unused openings?

They must be closed with identified closures
They may be left open indefinitely
They must be covered with duct tape only
The entire panelboard must be replaced

NEC Reference: NEC 408.7

Question 6: Which of the following circuit directory entries satisfies NEC 408.4(A)?

"Kitchen receptacles"
"Bill's office"
"Circuit"
Leaving the entry blank

NEC Reference: NEC 408.4(A)

Question 7: In a commercial building, a panelboard is supplied by a feeder. What field marking does NEC 408.4(B) require on that panelboard?

The name of the installing electrical contractor
The identification and location of the device or equipment where its power supply originates
The available fault current at the utility transformer only
The date of the last inspection

NEC Reference: NEC 408.4(B)

Question 8: NEC 240.24(D) prohibits overcurrent devices from being located in the vicinity of which of the following?

Easily ignitible material, such as a clothes closet
Concrete block walls
Metal framing
Ceramic tile

NEC Reference: NEC 240.24(D)

Question 9: Under NEC 240.24(E), overcurrent devices (other than supplementary protection) are generally prohibited from being located in:

Bathrooms and shower/locker rooms with showering facilities
Kitchens
Garages
Living rooms

NEC Reference: NEC 240.24(E)

Question 10: NEC 240.24(F) prohibits overcurrent devices from being located:

Directly over the steps of a stairway
In a mechanical room
In a hallway
In an attached garage

NEC Reference: NEC 240.24(F)

Question 11: What is the maximum height above the floor at which the operating handle of the highest circuit breaker in a panelboard may be mounted, per NEC 240.24?

5 ft
6 ft
6 ft 7 in
8 ft

NEC Reference: NEC 240.24

Question 12: NEC 404.2(B) prohibits a switch or circuit breaker from doing what to the grounded (neutral) conductor?

Disconnect it
Ground it a second time
Increase its size
Color it green

NEC Reference: NEC 404.2(B)

Question 13: Why does NEC 404.2(C) generally require a grounded conductor to be present at a switch location, even though switches never carry the neutral through their contacts?

To power the standby electronics in devices like dimmers and occupancy sensors
To let the switch disconnect the neutral safely
Because every switch box must always be grounded twice
It is a purely cosmetic labeling requirement

NEC Reference: NEC 404.2(C)

Question 14: Under the exceptions in NEC 404.2(C), a grounded conductor is not required to be extended to a switch box that:

Controls only a receptacle load
Is located in a kitchen
Is rated over 20A
Is installed outdoors

NEC Reference: NEC 404.2(C)

Question 15: An AC-DC general-use snap switch is used to control an inductive load. NEC 404.14 limits that load to what percentage of the switch's ampere rating?

25%
50%
80%
100%

NEC Reference: NEC 404.14

Question 16: When an AC-DC general-use snap switch is used for motor control duty, NEC 404.14 requires its ampere rating to be:

At least equal to the motor's FLC
At least 125% of the motor's FLC
At least twice (200%) the motor's FLC
At least five times the motor's FLC

NEC Reference: NEC 404.14

Question 17: Under NEC 430.109, a stationary motor rated 2 hp or less and 300V or less may use a general-use AC snap switch as its disconnect, provided:

The motor's FLC does not exceed 80% of the switch's ampere rating
The motor is three-phase only
The switch is rated for at least 600V
The motor is located outdoors

NEC Reference: NEC 430.109

Question 18: For most motor circuits outside the narrow small-motor exception, NEC 430.109 requires the disconnecting means to be:

A listed motor-circuit switch rated in horsepower
Any ordinary light switch
No disconnect at all
A doorbell transformer switch

NEC Reference: NEC 430.109

Question 19: Panelboards are generally required to be constructed with:

Dead-front construction, with no live parts exposed to the front
Exposed live busbars for easy testing
No enclosure of any kind
Clear plastic covers over energized parts, with no restriction on touching them

NEC Reference: NEC Article 408

Question 20: What generally distinguishes a switchboard from a panelboard?

A switchboard is typically larger and freestanding; a panelboard is enclosed in a wall-mounted cabinet
They are legally identical terms with no distinction
A panelboard is always larger than a switchboard
Only switchboards require any overcurrent protection

NEC Reference: NEC Article 408

Question 21: On a 3-phase, 4-wire delta-connected panelboard, which busbar position must the high leg (the phase with the higher voltage to ground) occupy under NEC 408.3(E)(1)?

Phase A
Phase B
Phase C
Any phase, as long as it is marked orange

NEC Reference: NEC 408.3(E)(1)

Question 22: A panelboard is installed where the available fault current is 22,000 A. The branch breakers are rated 10,000 A interrupting, and there is no listed series combination rating. Does this comply?

Yes — the panelboard's main breaker protects the branch breakers automatically
Yes — interrupting rating only matters for service equipment
No — the interrupting rating must be at least the available fault current (110.9) unless a listed series combination per 240.86 is used
Yes — as long as the branch breakers are 20 A or less

NEC Reference: NEC 110.9, 240.86

Question 23: NEC 408.43 prohibits panelboards from being installed:

In the face-up position
With the top of the enclosure more than 6 ft 7 in. above the floor
In an attached garage
On a concrete wall without spacers

NEC Reference: NEC 408.43

Question 24: A surface-mounted panelboard cabinet is installed on a wall in a damp location. What minimum airspace between the enclosure and the wall does NEC 312.2 require?

1/16 in.
1/8 in.
1/4 in.
1/2 in.

NEC Reference: NEC 312.2

Question 25: Feeder conductors with an ampacity of 130 A supply a panelboard rated 200 A. The calculated load is 120 A, and the feeder does not supply a multioutlet branch circuit for cord-and-plug loads. What is the largest feeder OCPD permitted?

125 A
130 A
150 A
200 A

NEC Reference: NEC 240.4(B), 408.36

Key NEC References for This Test

Article	What It Covers
Art. 220	Load Calculations — optional and standard methods for multifamily
Art. 230	Services — service design, sizing, multiple disconnects
Art. 430	Motors — complete branch circuit design (conductor + OCPD + overload + disconnect)
Art. 445	Generators — standby systems, transfer switches
Art. 450	Transformers — sizing, primary/secondary OCPD, installation
Art. 706	Energy Storage Systems — battery/solar storage (major NEC 2026 expansion)

Study Tip: Practice transformer kVA calculations daily. Know the formula: I = kVA × 1000 ÷ (V × 1.732) for three-phase. This comes up on almost every master exam.

Master Electrician Practice Test 22 – Panelboards, Switchboards & Switches

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Key NEC References for This Test

Master Electrician Practice Test 22 – Panelboards, Switchboards & Switches

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Master Electrician Practice Test 22 – Panelboards, Switchboards & Switches — Question List

Question 1: Under NEC 408.54, what is the maximum number of overcurrent devices permitted in a panelboard?

Question 2: NEC 408.36 requires the overcurrent device protecting a panelboard to have a rating:

Question 3: NEC 408.41 requires each grounded (neutral) conductor terminating in a panelboard to:

Question 4: A plug-in circuit breaker is installed back-fed and used as the main disconnect for a panelboard (common in some solar interconnections). What does NEC 408.36(D) require?

Question 5: A panelboard has two open breaker slots with no breakers installed. What does NEC 408.7 require for those unused openings?

Question 6: Which of the following circuit directory entries satisfies NEC 408.4(A)?

Question 7: In a commercial building, a panelboard is supplied by a feeder. What field marking does NEC 408.4(B) require on that panelboard?

Question 8: NEC 240.24(D) prohibits overcurrent devices from being located in the vicinity of which of the following?

Question 9: Under NEC 240.24(E), overcurrent devices (other than supplementary protection) are generally prohibited from being located in:

Question 10: NEC 240.24(F) prohibits overcurrent devices from being located:

Question 11: What is the maximum height above the floor at which the operating handle of the highest circuit breaker in a panelboard may be mounted, per NEC 240.24?

Question 12: NEC 404.2(B) prohibits a switch or circuit breaker from doing what to the grounded (neutral) conductor?

Question 13: Why does NEC 404.2(C) generally require a grounded conductor to be present at a switch location, even though switches never carry the neutral through their contacts?

Question 14: Under the exceptions in NEC 404.2(C), a grounded conductor is not required to be extended to a switch box that:

Question 15: An AC-DC general-use snap switch is used to control an inductive load. NEC 404.14 limits that load to what percentage of the switch's ampere rating?

Question 16: When an AC-DC general-use snap switch is used for motor control duty, NEC 404.14 requires its ampere rating to be:

Question 17: Under NEC 430.109, a stationary motor rated 2 hp or less and 300V or less may use a general-use AC snap switch as its disconnect, provided:

Question 18: For most motor circuits outside the narrow small-motor exception, NEC 430.109 requires the disconnecting means to be:

Question 19: Panelboards are generally required to be constructed with:

Question 20: What generally distinguishes a switchboard from a panelboard?

Question 21: On a 3-phase, 4-wire delta-connected panelboard, which busbar position must the high leg (the phase with the higher voltage to ground) occupy under NEC 408.3(E)(1)?

Question 22: A panelboard is installed where the available fault current is 22,000 A. The branch breakers are rated 10,000 A interrupting, and there is no listed series combination rating. Does this comply?

Question 23: NEC 408.43 prohibits panelboards from being installed:

Question 24: A surface-mounted panelboard cabinet is installed on a wall in a damp location. What minimum airspace between the enclosure and the wall does NEC 312.2 require?

Question 25: Feeder conductors with an ampacity of 130 A supply a panelboard rated 200 A. The calculated load is 120 A, and the feeder does not supply a multioutlet branch circuit for cord-and-plug loads. What is the largest feeder OCPD permitted?

Key NEC References for This Test

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