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NEC CODE NEC 2020

Panelboards and Switchboards (NEC 408) — NEC 2020 Edition

Free NEC 2020 practice test on panelboards and switchboards. Covers overcurrent protection, wet-location clearances, neutral terminal rules, high-leg (wild leg) marking, and transformer-fed panelboard protection. Simple English, full explanations.

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The National Electrical Code (NFPA 70) is the benchmark standard for safe electrical installation in the US. It is updated every 3 years by the NFPA.

Study the edition adopted by your state. As of 2025, most states use the 2020 or 2023 NEC. These tests are written to the 2023 edition.

The most tested articles are 100 (Definitions), 200–250 (Wiring & Grounding), 300–314 (Wiring Methods), 400–411 (Conductors), 430 (Motors), and 700–701 (Emergency Systems).

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This Panelboards and Switchboards (NEC 408) — NEC 2020 Edition has 30 questions with detailed answers and NEC references. Take the full test, review every wrong answer, and look up the NEC article it references before moving on.

Tip: Use the NEC index (back of the book) — find answers by keyword, not by article number.

Topics covered: NEC articles 100, 210, 220, 240, 250, 300, 310, 430, and special occupancies.
Passing score: Aim for 80%+ on NEC code tests before exam day.
Questions: 30 multiple-choice, one correct answer each

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Panelboards and Switchboards (NEC 408) — NEC 2020 Edition — Question List

Question 1: In a panelboard, may two grounded (neutral) conductors be connected under one terminal?

Yes, if the panel is in a dwelling
Yes, always
No, unless the terminal is identified for more than one conductor
Yes, if both are the same size

NEC Reference: NEC 408.41

Question 2: When a panelboard enclosure is mounted in a wet location, how much air space is generally required between the enclosure and the mounting surface?

1/4 inch
1/2 inch
3/4 inch
1 inch

NEC Reference: NEC 312.2(A)

Question 3: When a panelboard is supplied by a transformer, the panelboard's overcurrent protection must generally be placed on which side of the transformer?

Primary
Secondary
Neither side
Both sides equally required

NEC Reference: NEC 408.36(B)

Question 4: The rating of the overcurrent protective device supplying a panelboard should generally be what, compared to the panelboard's own rating?

Not be greater than the panelboard rating
Be 125% of the panelboard rating
Be greater than the panelboard rating
Be 115% of the panelboard rating

NEC Reference: NEC 408.36

Question 5: On a 3-phase, 4-wire delta system with a high-leg (wild leg) conductor, that high-leg conductor must terminate on which phase (bus position) of the panelboard or switchboard?

A, or first phase
B, or center phase
C, or third phase
Any phase, no restriction

NEC Reference: NEC 408.3(E)

Question 6: Where accessible, the high-leg (wild leg) conductor of a 4-wire delta system must be identified by what color?

Orange
Green
Blue
White

NEC Reference: NEC 110.15

Question 7: For a switchboard rated 0-150 volts to ground under Condition 1, what is the minimum required clear working space depth?

3 feet
1 foot
6 feet
10 feet

NEC Reference: NEC Table 110.26(A)(1)

Question 8: Where must a panelboard circuit directory be located?

On the utility meter enclosure
On the face, inside the door, or in an approved location next to the panelboard
In the building maintenance office
Only on the as-built drawings

NEC Reference: NEC 408.4(A)

Question 9: What limits the number of overcurrent devices that may be installed in a panelboard?

A fixed maximum of 42 devices
A fixed maximum of 30 devices
The number of spaces the electrician can fit
The number for which the panelboard is designed, rated and listed

NEC Reference: NEC 408.54

Question 10: What must the rating of a panelboard be at least?

The minimum feeder capacity for the load calculated under Article 220
Twice the connected load
The rating of the service
The sum of all its breaker ratings

NEC Reference: NEC 408.30

Question 11: How must panelboards be enclosed?

In an open frame with a guard rail
In a nonmetallic box only
In cabinets or cutout boxes, and of dead-front construction
In any metal box with exposed bus

NEC Reference: NEC 408.38

Question 12: A panelboard is installed in a wet location. What rule applies to its enclosure?

It must be raised 3 ft above the floor
It needs only a gasketed front cover
312.2: weatherproof and installed to prevent moisture from accumulating
No special rule applies indoors

NEC Reference: NEC 408.37

Question 13: A panelboard is supplied through nonmetallic raceway. What must be provided inside the cabinet for the equipment grounding conductors?

A separate ground rod
A terminal bar bonded to the cabinet
Nothing; the neutral bar is used
A splice box outside the panel

NEC Reference: NEC 408.40

Question 14: A switchboard rated 1,200 A is more than 6 ft wide. What does 110.26(C)(2) require for its working space?

An entrance at each end of the working space
A fire-rated door only
One entrance at the center only
No special entrance rules

NEC Reference: NEC 110.26(C)(2)

Question 15: At the service, which component connects the equipment grounding conductors to the grounded (neutral) conductor?

The system bonding jumper of a transformer
The grounding electrode conductor
An equipment bonding jumper at each subpanel
The main bonding jumper

NEC Reference: NEC 250.28

Question 16: In a subpanel fed by a feeder from the service, how are the grounded (neutral) and equipment grounding conductors terminated?

On separate, isolated bars
On the same bar, bonded together
Either way is permitted
Neutrals to the enclosure, grounds to a rod

NEC Reference: NEC 250.142(B)

Question 17: Service equipment in a building other than a dwelling unit must be field marked with what?

The utility transformer size only
The installer's license number
The maximum available fault current and the date of the calculation
The arc-flash PPE category

NEC Reference: NEC 110.24(A)

Question 18: How must unused breaker openings in a panelboard be closed?

They may be left open in dwelling units
With the removed knockout taped back in place
With a blank breaker of any brand
With identified closures or equal protection

NEC Reference: NEC 408.7

Question 19: A switchboard that is not totally enclosed is installed under a combustible ceiling. What minimum space is required above it?

3 ft
1 ft
18 in.
6 ft

NEC Reference: NEC 408.18(A)

Question 20: Minimum wire-bending space at terminals in cabinets and cutout boxes is found in which tables?

Table 310.16
Tables 312.6(A) and 312.6(B)
Table 314.16(A)
Chapter 9, Table 1

NEC Reference: NEC 312.6

Question 21: Barriers are required in service switchboards and panelboards so that what is not exposed while load terminations are serviced?

The neutral bar
Uninsulated, ungrounded service busbars and terminals
The equipment grounding bar
The branch-circuit breakers

NEC Reference: NEC 408.3(A)(2)

Question 22: A back-fed circuit breaker supplies power into a panelboard (other than as permitted for listed interactive inverters). How must it be secured?

It needs no special securing
With a handle tie only
With an additional fastener that requires other than a pull to release
With electrical tape over the handle

NEC Reference: NEC 408.36(D)

Question 23: What is the minimum height of the working space in front of a panelboard (unless the equipment is taller)?

6 ft
6½ ft
7 ft
8 ft

NEC Reference: NEC 110.26(A)(3)

Question 24: What does the NEC require for indoor working spaces around service equipment, switchboards and panelboards?

Illumination
A fire extinguisher
A dedicated HVAC supply
A floor drain

NEC Reference: NEC 110.26(D)

Question 25: Where multiple service disconnects are grouped at a single switchboard location, per NEC 230.71, what is the maximum number generally allowed for most occupancies?

6
2
10
There is no limit

NEC Reference: NEC 230.71(B)

Question 26: In other than one- and two-family dwellings, a panelboard supplied by a feeder must be marked with what?

The name of the electrician
The building square footage
The date of installation
Where its power supply originates

NEC Reference: NEC 408.4(B)

Question 27: On a 3-phase panelboard or switchboard bus, what is the required phase arrangement?

A, B, C from front to back, top to bottom, or left to right
Any order, if marked
B phase always on the left
C, B, A from left to right

NEC Reference: NEC 408.3(E)(1)

Question 28: Which circuit directory description is NOT acceptable under 408.4(A)?

"Furnace - basement"
"Exterior lights - front entry"
"Kitchen counter receptacles, north wall"
"Bob's office"

NEC Reference: NEC 408.4(A)

Question 29: A feeder from the main building supplies a separate detached building. What is required for that building?

A second service drop
A disconnecting means for the conductors supplying it
Nothing beyond the feeder breaker in the main building
A separate utility meter

NEC Reference: NEC 225.31

Question 30: Equipment protected by a tested series combination rating must be field marked to show what?

The installation date only
The available fault current only
That it is series rated and identified replacement components are required
The name of the testing laboratory

NEC Reference: NEC 110.22(C)

Key NEC References for This Test

Article	What It Covers
Ch. 1–4	General rules — apply to all installations
Ch. 5–7	Special rules — override Ch. 1–4 where they conflict
Ch. 8	Communications — completely independent of Ch. 1–7
Ch. 9	Tables — referenced by articles, not standalone enforceable rules
Art. 210.12	AFCI — major expansion in NEC 2026
Art. 230.67	Surge protection at service equipment — new NEC 2026

Study Tip: Learn the NEC index — use keywords, not article numbers. Practice finding 5 different topics in under 2 minutes each.

Panelboards and Switchboards (NEC 408) — NEC 2020 Edition

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Panelboards and Switchboards (NEC 408) — NEC 2020 Edition — Question List

Question 1: In a panelboard, may two grounded (neutral) conductors be connected under one terminal?

Question 2: When a panelboard enclosure is mounted in a wet location, how much air space is generally required between the enclosure and the mounting surface?

Question 3: When a panelboard is supplied by a transformer, the panelboard's overcurrent protection must generally be placed on which side of the transformer?

Question 4: The rating of the overcurrent protective device supplying a panelboard should generally be what, compared to the panelboard's own rating?

Question 5: On a 3-phase, 4-wire delta system with a high-leg (wild leg) conductor, that high-leg conductor must terminate on which phase (bus position) of the panelboard or switchboard?

Question 6: Where accessible, the high-leg (wild leg) conductor of a 4-wire delta system must be identified by what color?

Question 7: For a switchboard rated 0-150 volts to ground under Condition 1, what is the minimum required clear working space depth?

Question 8: Where must a panelboard circuit directory be located?

Question 9: What limits the number of overcurrent devices that may be installed in a panelboard?

Question 10: What must the rating of a panelboard be at least?

Question 11: How must panelboards be enclosed?

Question 12: A panelboard is installed in a wet location. What rule applies to its enclosure?

Question 13: A panelboard is supplied through nonmetallic raceway. What must be provided inside the cabinet for the equipment grounding conductors?

Question 14: A switchboard rated 1,200 A is more than 6 ft wide. What does 110.26(C)(2) require for its working space?

Question 15: At the service, which component connects the equipment grounding conductors to the grounded (neutral) conductor?

Question 16: In a subpanel fed by a feeder from the service, how are the grounded (neutral) and equipment grounding conductors terminated?

Question 17: Service equipment in a building other than a dwelling unit must be field marked with what?

Question 18: How must unused breaker openings in a panelboard be closed?

Question 19: A switchboard that is not totally enclosed is installed under a combustible ceiling. What minimum space is required above it?

Question 20: Minimum wire-bending space at terminals in cabinets and cutout boxes is found in which tables?

Question 21: Barriers are required in service switchboards and panelboards so that what is not exposed while load terminations are serviced?

Question 22: A back-fed circuit breaker supplies power into a panelboard (other than as permitted for listed interactive inverters). How must it be secured?

Question 23: What is the minimum height of the working space in front of a panelboard (unless the equipment is taller)?

Question 24: What does the NEC require for indoor working spaces around service equipment, switchboards and panelboards?

Question 25: Where multiple service disconnects are grouped at a single switchboard location, per NEC 230.71, what is the maximum number generally allowed for most occupancies?

Question 26: In other than one- and two-family dwellings, a panelboard supplied by a feeder must be marked with what?

Question 27: On a 3-phase panelboard or switchboard bus, what is the required phase arrangement?

Question 28: Which circuit directory description is NOT acceptable under 408.4(A)?

Question 29: A feeder from the main building supplies a separate detached building. What is required for that building?

Question 30: Equipment protected by a tested series combination rating must be field marked to show what?

Key NEC References for This Test

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