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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).

How to Use This Practice Test

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, can two neutral (grounded) conductors terminate under the same screw terminal?

True -- each needs its own terminal
False -- they can always share
Only in a metal enclosure
Only for circuits under 20A

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: A panelboard's circuit directory must be located where, and describe what?

On the panel door, with a clear description of each circuit
Nowhere -- it is optional
Only in a separate binder kept off site
Only in the electrician's personal notes

NEC Reference: NEC 408.4(A)

Question 9: Per NEC 408.54, what is the maximum number of overcurrent devices generally permitted in a lighting and appliance branch-circuit panelboard, unless listed for more?

NEC Reference: NEC 408.54

Question 10: A panelboard must be rated for the voltage and what other electrical characteristic of the circuits it supplies?

The current (ampere) rating
The paint color
The manufacturer's founding date
Nothing else matters

NEC Reference: NEC 408.30

Question 11: Panelboards must generally be installed in what type of enclosure, to prevent accidental contact with live parts?

A dead-front enclosure
An open frame with no cover
A cardboard box
No enclosure is needed

NEC Reference: NEC 408.38

Question 12: Indoor switchboards and panelboards not identified for damp or wet locations must generally be protected against what?

Moisture and physical damage
Sunlight only
Nothing -- no protection needed
Noise only

NEC Reference: NEC 408.55

Question 13: A panelboard's metal enclosure must generally be what, connecting it to the equipment grounding system?

Grounded and bonded
Insulated from ground
Painted only
Left floating electrically

NEC Reference: NEC 408.40

Question 14: Switchboards must generally be located to provide what type of access for maintenance and operation?

Sufficient access and working space
No access is required
Access only once a year
Access only through a locked vault with no key held onsite

NEC Reference: NEC 110.26

Question 15: When a panelboard is used as service equipment, what must connect the grounded (neutral) conductor to the equipment grounding system, within that panelboard?

The main bonding jumper
A telephone wire
Nothing is required
A gas pipe only

NEC Reference: NEC 250.28

Question 16: In a subpanel (panelboard downstream of the service), should the neutral and equipment grounding conductors generally be bonded together?

No, they must be kept separate
Yes, always bond them together
It does not matter at all
Only on weekends

NEC Reference: NEC 250.24(A)(5)

Question 17: Service equipment, including panelboards used as such, must generally be marked with what rating related to fault conditions?

Available fault current, with the calculation date
The installer's favorite color
Nothing at all
Only the purchase price

NEC Reference: NEC 110.24

Question 18: Unused openings in a panelboard where a breaker could be installed must generally be what?

Closed with a listed closure
Left open permanently
Covered with tape only
Filled with insulation foam

NEC Reference: NEC 408.7

Question 19: For a rear-accessible switchboard requiring rear access for connections, what must be provided at the back?

Adequate rear working space
No rear access is ever needed
A locked door with no key onsite
A ladder only, no floor space

NEC Reference: NEC 110.26

Question 20: Cabinets and panelboards must generally provide adequate what for the conductors entering them?

Wire-bending space
Extra paint
A window for viewing
Nothing is required

NEC Reference: NEC 312.6

Question 21: Where service conductors of different systems enter the same switchboard section, what is generally required?

Barriers between the different systems
No separation is needed
A single shared busbar for everything
Removing one of the systems entirely

NEC Reference: NEC 408.3(B)

Question 22: A back-fed circuit breaker in a panelboard, such as one used for a solar PV interconnection, must generally be secured how?

With an additional fastener beyond a simple pull
With tape only
It never needs securing
With glue

NEC Reference: NEC 408.36(D)

Question 23: Switchboards and panelboards should generally be installed with attention to nearby combustible material because of what risk?

Heat and arc energy fire risk
No risk at all
Only a cosmetic concern
Only a noise concern

NEC Reference: NEC 110.3(B)

Question 24: Panelboards installed under the NEC must generally be what, to confirm they meet applicable safety standards?

Listed and labeled
Homemade only
Unlisted is preferred
Nothing is required

NEC Reference: NEC 110.3(B)

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(A)

Question 26: Can a panelboard use fusible switches instead of circuit breakers for its overcurrent protection?

Yes, if properly listed and rated
No, only breakers are ever allowed
Only in hospitals
Only for circuits under 15A

NEC Reference: NEC Article 408

Question 27: Busbars and conductors within a switchboard must generally be spaced or insulated to prevent what?

Accidental short circuits or grounds
Nothing -- spacing does not matter
Only cosmetic issues
Only noise issues

NEC Reference: NEC 408.3

Question 28: Circuit breakers or fuses within a panelboard installed for branch circuits should generally be arranged so that operation is what for the technician?

Clear, safe, and orderly
Confusing on purpose
Hidden behind a wall permanently
Randomly arranged with no labels

NEC Reference: NEC Article 408

Question 29: Feeders supplying a second building from a switchboard in the first building generally require what at the second building?

A disconnecting means
Nothing at all
A second utility meter only
A padlock with no disconnect

NEC Reference: NEC 225.31

Question 30: Where a panelboard uses a series-rated combination of overcurrent devices for its short-circuit rating, what must be marked on the equipment?

A field marking noting the series rating and replacement requirement
Nothing needs to be marked
Only the manufacturer's logo
Only the installation date

NEC Reference: NEC 110.22(B)

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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Key NEC References for This Test

Panelboards and Switchboards (NEC 408) — NEC 2020 Edition

How this test works

Frequently Asked Questions

Is this Panelboards and Switchboards (NEC 408) — NEC 2020 Edition free?

What is the NEC code book?

Which NEC edition should I study?

What articles are covered on electrician licensing exams?

How to Use This Practice Test

Student Reviews

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

Question 1: In a panelboard, can two neutral (grounded) conductors terminate under the same screw 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: A panelboard's circuit directory must be located where, and describe what?

Question 9: Per NEC 408.54, what is the maximum number of overcurrent devices generally permitted in a lighting and appliance branch-circuit panelboard, unless listed for more?

Question 10: A panelboard must be rated for the voltage and what other electrical characteristic of the circuits it supplies?

Question 11: Panelboards must generally be installed in what type of enclosure, to prevent accidental contact with live parts?

Question 12: Indoor switchboards and panelboards not identified for damp or wet locations must generally be protected against what?

Question 13: A panelboard's metal enclosure must generally be what, connecting it to the equipment grounding system?

Question 14: Switchboards must generally be located to provide what type of access for maintenance and operation?

Question 15: When a panelboard is used as service equipment, what must connect the grounded (neutral) conductor to the equipment grounding system, within that panelboard?

Question 16: In a subpanel (panelboard downstream of the service), should the neutral and equipment grounding conductors generally be bonded together?

Question 17: Service equipment, including panelboards used as such, must generally be marked with what rating related to fault conditions?

Question 18: Unused openings in a panelboard where a breaker could be installed must generally be what?

Question 19: For a rear-accessible switchboard requiring rear access for connections, what must be provided at the back?

Question 20: Cabinets and panelboards must generally provide adequate what for the conductors entering them?

Question 21: Where service conductors of different systems enter the same switchboard section, what is generally required?

Question 22: A back-fed circuit breaker in a panelboard, such as one used for a solar PV interconnection, must generally be secured how?

Question 23: Switchboards and panelboards should generally be installed with attention to nearby combustible material because of what risk?

Question 24: Panelboards installed under the NEC must generally be what, to confirm they meet applicable safety standards?

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: Can a panelboard use fusible switches instead of circuit breakers for its overcurrent protection?

Question 27: Busbars and conductors within a switchboard must generally be spaced or insulated to prevent what?

Question 28: Circuit breakers or fuses within a panelboard installed for branch circuits should generally be arranged so that operation is what for the technician?

Question 29: Feeders supplying a second building from a switchboard in the first building generally require what at the second building?

Question 30: Where a panelboard uses a series-rated combination of overcurrent devices for its short-circuit rating, what must be marked on the equipment?

Key NEC References for This Test

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