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MASTER NEC 2023

Master Electrician Practice Test 17 – Conductors, Cables & Ampacity

This is Master Electrician Practice Test 17 — Conductors, Cables & Ampacity, covering the general wiring rules of Article 300, the conductor selection and ampacity rules of Article 310, and flexible cord rules from Article 400. The test has 25 multiple-choice questions on ampacity table basics, insulation types, physical protection of conductors, splice and support rules, free-conductor length at boxes, and where flexible cords may and may not be used. 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

Conductors, Cables & Ampacity

How this test works

Read each question carefully

Look for absolute words like always / never — they often distinguish the right answer.

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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

Table 310.16 ampacities baseline — 3 current-carrying conductors, 30°C ambient
Bundling adjustment trigger — bundled longer than 24 inches (NEC 310.15(C)(1))
XHHW-2 insulation — 90°C rating in both wet and dry locations
Physical protection of conductors through framing members — 1.25 in or steel plate (NEC 300.4(A))
Raceways/cables not supported by ceiling grid or support wires (NEC 300.11(C))
Multiwire branch circuit neutral continuity — pigtail required at devices (NEC 300.13(B))
Minimum 6 in of free conductor at outlet/junction/switch points (NEC 300.14)
Minimum 3 in of conductor extending beyond the box opening (NEC 300.14)
Flexible cords not permitted as a substitute for fixed wiring (NEC 400.12)
Conductors 8 AWG and larger must be stranded in raceways (NEC 310.3(A))
90°C ampacity column used for derating math, capped by termination rating (NEC 110.14(C))
Sealing raceways between different temperature zones to prevent condensation (NEC 300.7(A))
Box or conduit body required at splice and pull points (NEC 300.15)
THHN vs. THWN-2/XHHW-2 — dry-only vs. wet-and-dry ratings
Permitted uses of flexible cords and cables (NEC 400.10)
Ungrounded conductor color — no NEC-mandated color except the high-leg (NEC 230.56)
USE cable vs. SE cable — suitability for direct burial
NM cable — 90°C conductor rating capped at the 60°C ampacity column (NEC 334.80)
Type UF cable — suitable for direct burial
Physical protection height for underground conductors emerging above grade (NEC 300.5(D)(1))
Chapter 9 — home of the raceway and box fill tables
Applying the bundling adjustment to a long conductor run
Combining temperature correction and bundling adjustment factors — multiply, don't add
Relationship between Article 300 (general wiring methods) and Article 310 (conductors)

Tip: A 90°C-rated conductor gives you more room to apply correction and adjustment factors, but the final selected ampacity can never exceed the ampacity for the lowest temperature rating in the circuit — usually the terminal rating, per 110.14(C).

Questions

45 min

Time

70%

Pass

Timer starts immediately. Progress is auto-saved.

Master Electrician Practice Test 17 – Conductors, Cables & Ampacity — Question List

Question 1: The ampacities listed in NEC Table 310.16 apply without adjustment for how many current-carrying conductors in a raceway or cable?

One
Three
Six
Ten

NEC Reference: NEC Table 310.16

Question 2: Per NEC 310.15(C)(1), the conductor bundling adjustment factors apply when current-carrying conductors are bundled together without maintaining spacing for a distance longer than:

6 inches
12 inches
24 inches
10 feet

NEC Reference: NEC 310.15(C)(1)

Question 3: Which conductor insulation type retains its 90 degrees C ampacity rating in BOTH wet and dry locations?

THHN (alone)
XHHW-2
TW
UF (standard)

NEC Reference: NEC Table 310.104(A)

Question 4: NEC 300.4(A)(1) requires conductors run through bored holes in wood framing members to maintain what minimum distance from the nearest edge of the framing member, or otherwise be protected?

0.5 inch
1.25 inches
3 inches
6 inches

NEC Reference: NEC 300.4(A)(1)

Question 5: NEC 300.11(C) prohibits raceways and cables from being supported by:

The suspended ceiling grid or its support wires
Listed cable straps only
Rigid metal conduit hangers
Approved framing members

NEC Reference: NEC 300.11(C)

Question 6: NEC 300.13(B) requires the continuity of the grounded (neutral) conductor in a multiwire branch circuit to:

Not depend on the connection of any device (a pigtail must be used)
Always run through the device's feed-through terminals
Be interrupted at every receptacle intentionally
Never be spliced under any circumstances

NEC Reference: NEC 300.13(B)

Question 7: NEC 300.14 requires at least how much free conductor length to be left at each outlet, junction, and switch point for splices or device connections?

3 inches
6 inches
12 inches
18 inches

NEC Reference: NEC 300.14

Question 8: Of the 6 in of free conductor NEC 300.14 requires at an outlet or junction point, how much of that must extend outside (beyond) the box opening?

1 inch
3 inches
6 inches (all of it)
9 inches

NEC Reference: NEC 300.14

Question 9: NEC 400.12 prohibits flexible cords and cables from being used:

As a substitute for the fixed wiring of a structure
To supply a portable table lamp
To supply a portable power tool
On an elevator car

NEC Reference: NEC 400.12

Question 10: NEC 310.3(A) requires conductors of what size and larger to be stranded when installed in a raceway?

14 AWG
10 AWG
8 AWG
4/0 AWG

NEC Reference: NEC 310.3(A)

Question 11: A 90 degrees C-rated conductor is used with equipment terminals rated only 75 degrees C. How does NEC 110.14(C) direct you to select the final conductor ampacity?

Always use the 90 degrees C column, with no cap
Use the 90 degrees C column for derating, but cap the final ampacity at the 75 degrees C column value
Use the 60 degrees C column regardless of the conductor's actual rating
Ampacity selection is unaffected by terminal rating

NEC Reference: NEC 110.14(C)

Question 12: NEC 300.7(A) requires raceways passing between areas of substantially different temperature, such as a run entering a refrigerated space, to be:

Filled with an approved material to prevent air circulation and condensation
Left open at both ends to promote airflow
Wrapped in aluminum foil
Painted white to reflect heat

NEC Reference: NEC 300.7(A)

Question 13: NEC 300.15 generally requires what to be installed at every point where conductors are spliced or where a pull is made?

A box or conduit body
Nothing — splices may be made freely inside a raceway with no access point
A ground rod
A surge protective device

NEC Reference: NEC 300.15

Question 14: The 30 degrees C ambient temperature referenced in Table 310.16 represents:

The maximum allowable conductor temperature
The baseline ambient temperature the listed ampacities assume
The minimum installation temperature for PVC conduit
The freezing point safety margin

NEC Reference: NEC Table 310.16

Question 15: A conductor is marked "THHN/THWN-2" on its jacket. What does this dual marking tell an installer?

It is rated 90 degrees C dry and up to 90 degrees C wet (per THWN-2)
It may only be used in dry indoor locations
It is rated for only 60 degrees C in any location
The marking has no meaning under the NEC

NEC Reference: NEC Table 310.104(A)

Question 16: Which of the following is a permitted use of flexible cords and cables under NEC 400.10?

Pendant lighting and portable appliance connections
Permanent feeder wiring concealed in a wall
Service-entrance conductors
Underground feeder wiring

NEC Reference: NEC 400.10

Question 17: Aside from the high-leg conductor of a 4-wire delta system, does the NEC generally mandate a specific color for ungrounded (hot) conductors?

No — there is no general NEC-mandated color for ordinary ungrounded conductors
Yes — every ungrounded conductor must be black by NEC mandate
Yes — every ungrounded conductor must be red by NEC mandate
Yes — every ungrounded conductor must be blue by NEC mandate

NEC Reference: NEC 230.56 / general practice

Question 18: Which cable type is specifically suitable for direct burial without additional raceway protection, unlike ordinary SE cable?

Type SE cable
Type USE cable
Type AC cable
Type MI cable only

NEC Reference: NEC Article 338

Question 19: NM cable (Romex) conductors are internally rated 90 degrees C, but NEC 334.80 requires the cable's usable ampacity to be based on which column?

The 90 degrees C column, with no restriction
The 60 degrees C column
The 75 degrees C column, always
There is no ampacity cap for NM cable

NEC Reference: NEC 334.80

Question 20: Type UF (Underground Feeder) cable, per NEC Article 340, is suitable for:

Direct burial in the earth, per 300.5
Indoor dry locations only, never buried
Service-entrance conductors exclusively
Class 1 power-limited circuits only

NEC Reference: NEC Article 340

Question 21: NEC 300.5(D)(1) requires direct-buried underground conductors that emerge above grade to be protected from physical damage up to a point at least how high above finished grade?

3 feet
5 feet
8 feet
15 feet

NEC Reference: NEC 300.5(D)(1)

Question 22: The raceway and box conductor fill tables referenced throughout Articles 300 and 310 are located in which chapter of the NEC?

Chapter 3
Chapter 5
Chapter 9
Chapter 1

NEC Reference: NEC Chapter 9

Question 23: Eight current-carrying 12 AWG THHN conductors are bundled together with no maintained spacing for a 10 ft run inside one conduit. Do the NEC 310.15(C)(1) bundling adjustment factors apply?

No — 10 ft is too short a run to trigger the adjustment
Yes — the 10 ft run far exceeds the 24 in trigger, so an adjustment factor applies
Only if the conductors are aluminum
Only in wet locations

NEC Reference: NEC 310.15(C)(1)

Question 24: When both an ambient temperature correction factor (310.15(B)(1)) and a conductor bundling adjustment factor (310.15(C)(1)) apply to the same circuit, how should they be combined?

Add the two percentages together
Multiply the two factors together, then apply to the base ampacity
Use only the larger of the two factors and ignore the other
Apply only the smaller factor, since it is more conservative

NEC Reference: NEC 310.15

Question 25: How do Article 300 and Article 310 divide responsibility for a typical branch-circuit installation?

Article 300 covers general wiring methods; Article 310 covers conductor construction and ampacity
Article 310 replaces Article 300 entirely
Article 300 applies only to services; Article 310 applies only to feeders
They cover entirely unrelated, non-overlapping topics

NEC Reference: NEC Articles 300 and 310

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 17 – Conductors, Cables & Ampacity

How this test works

Frequently Asked Questions

Before You Start

Topics in This Test

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Key NEC References for This Test

Master Electrician Practice Test 17 – Conductors, Cables & Ampacity

How this test works

Frequently Asked Questions

Is this Master Electrician Practice Test 17 – Conductors, Cables & Ampacity free?

How do I qualify for the Master Electrician exam?

What is covered on the Master Electrician exam?

How is the Master exam different from the Journeyman exam?

Before You Start

Topics in This Test

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Master Electrician Practice Test 17 – Conductors, Cables & Ampacity — Question List

Question 1: The ampacities listed in NEC Table 310.16 apply without adjustment for how many current-carrying conductors in a raceway or cable?

Question 2: Per NEC 310.15(C)(1), the conductor bundling adjustment factors apply when current-carrying conductors are bundled together without maintaining spacing for a distance longer than:

Question 3: Which conductor insulation type retains its 90 degrees C ampacity rating in BOTH wet and dry locations?

Question 4: NEC 300.4(A)(1) requires conductors run through bored holes in wood framing members to maintain what minimum distance from the nearest edge of the framing member, or otherwise be protected?

Question 5: NEC 300.11(C) prohibits raceways and cables from being supported by:

Question 6: NEC 300.13(B) requires the continuity of the grounded (neutral) conductor in a multiwire branch circuit to:

Question 7: NEC 300.14 requires at least how much free conductor length to be left at each outlet, junction, and switch point for splices or device connections?

Question 8: Of the 6 in of free conductor NEC 300.14 requires at an outlet or junction point, how much of that must extend outside (beyond) the box opening?

Question 9: NEC 400.12 prohibits flexible cords and cables from being used:

Question 10: NEC 310.3(A) requires conductors of what size and larger to be stranded when installed in a raceway?

Question 11: A 90 degrees C-rated conductor is used with equipment terminals rated only 75 degrees C. How does NEC 110.14(C) direct you to select the final conductor ampacity?

Question 12: NEC 300.7(A) requires raceways passing between areas of substantially different temperature, such as a run entering a refrigerated space, to be:

Question 13: NEC 300.15 generally requires what to be installed at every point where conductors are spliced or where a pull is made?

Question 14: The 30 degrees C ambient temperature referenced in Table 310.16 represents:

Question 15: A conductor is marked "THHN/THWN-2" on its jacket. What does this dual marking tell an installer?

Question 16: Which of the following is a permitted use of flexible cords and cables under NEC 400.10?

Question 17: Aside from the high-leg conductor of a 4-wire delta system, does the NEC generally mandate a specific color for ungrounded (hot) conductors?

Question 18: Which cable type is specifically suitable for direct burial without additional raceway protection, unlike ordinary SE cable?

Question 19: NM cable (Romex) conductors are internally rated 90 degrees C, but NEC 334.80 requires the cable's usable ampacity to be based on which column?

Question 20: Type UF (Underground Feeder) cable, per NEC Article 340, is suitable for:

Question 21: NEC 300.5(D)(1) requires direct-buried underground conductors that emerge above grade to be protected from physical damage up to a point at least how high above finished grade?

Question 22: The raceway and box conductor fill tables referenced throughout Articles 300 and 310 are located in which chapter of the NEC?

Question 23: Eight current-carrying 12 AWG THHN conductors are bundled together with no maintained spacing for a 10 ft run inside one conduit. Do the NEC 310.15(C)(1) bundling adjustment factors apply?

Question 24: When both an ambient temperature correction factor (310.15(B)(1)) and a conductor bundling adjustment factor (310.15(C)(1)) apply to the same circuit, how should they be combined?

Question 25: How do Article 300 and Article 310 divide responsibility for a typical branch-circuit installation?

Key NEC References for This Test

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