Color/marking identification of grounded conductors by size
NEC 200.6 Grounded conductors are identified by continuous white or gray insulation (or stripes/markings for larger sizes) — never green, which is reserved for equipment grounding.
Q1 NEC 200.6
Which identification method is NOT permitted for an insulated grounded conductor sized 4 AWG or larger?
- A A continuous gray outer finish
- B A distinctive white or gray marking encircling the insulation at terminations
- C A continuous white outer finish
- D Three continuous stripes in any color along the insulation
Show answer & explanation
Correct: D — Three continuous stripes in any color along the insulation
200.6(B) allows continuous white, continuous gray, three white or gray stripes on other than green insulation, or a distinctive termination marking. The stripe option specifically requires white or gray stripes, not stripes 'in any color,' so that option is not permitted.
Neutral conductor installation and multi-circuit identification
NEC 200.4 One neutral serves one circuit — sharing across circuits or feeders needs specific Code permission, and shared enclosures require neutrals to be grouped or identified.
Q2 NEC 200.4
An installer wants to run one neutral conductor to serve two separate multiwire branch circuits in a panel to save wire. Is this permitted?
- A Yes, as long as the two circuits are on opposite phases
- B No, a neutral conductor cannot be used for more than one multiwire branch circuit
- C Yes, provided both circuits are protected by a single two-pole breaker
- D Yes, if the shared neutral is upsized to handle the combined load
Show answer & explanation
Correct: B — No, a neutral conductor cannot be used for more than one multiwire branch circuit
200.4(A) prohibits using a neutral conductor for more than one multiwire branch circuit, regardless of phasing, wire size, or shared overcurrent protection. Those workarounds don't create an exception.
Identifying device terminals for the grounded conductor
NEC 200.9 The terminal for the grounded conductor is always white or silver (or marked 'W'), and on screw-shell devices that terminal is the shell itself.
Q3 NEC 200.9
A receptacle's grounded-conductor terminal is not visible from outside the device. Per 200.10(B), how must the termination point still be identified?
- A The conductor entrance hole is colored white or marked 'white' or 'W'
- B Identification is required only on the ungrounded terminal in that case
- C The terminal must use silver-plated metal only, without any letter marking
- D No identification is required once the terminal is hidden from view
Show answer & explanation
Correct: A — The conductor entrance hole is colored white or marked 'white' or 'W'
200.10(B)(2) requires that if the terminal isn't visible, the conductor entrance hole itself be colored white or marked 'white' or 'W.' Skipping identification, requiring metal-only marking, or shifting the requirement to the ungrounded terminal all contradict the rule.
When white or gray insulation may be used for ungrounded conductors
NEC 200.7 White or gray insulation is reserved for the grounded conductor, except for reidentified cable conductors and certain flexible-cord conductors.
Q4 NEC 200.7
An electrician wants to use a cable assembly's white conductor as an ungrounded conductor on a 120-volt circuit. Per 200.7(C), what must be done everywhere the conductor is visible or accessible?
- A It must be replaced with black conductor for the full run
- B It must be reidentified only at the panel where the circuit originates
- C It must carry a printed tag stating the circuit number
- D It must be permanently reidentified with tape, paint, or similar means, in a color other than white, gray, or green
Show answer & explanation
Correct: D — It must be permanently reidentified with tape, paint, or similar means, in a color other than white, gray, or green
200.7(C) requires reidentification at the termination and at every point the conductor is visible or accessible, not just at the panel. A printed circuit-number tag or a full conductor swap isn't what the rule calls for.
Surge protection required on feeders to dwellings and sleeping units
NEC 215.18 Feeders serving dwelling units, dormitories, hotel/motel guest rooms, or nursing home sleeping rooms need a Type 1 or Type 2 SPD rated at least 10kA at the distribution equipment — even on replacements.
Q5 NEC 215.18
A feeder supplies the branch-circuit panelboard for a hotel's guest rooms. Per 215.18, what must be installed at or near that panelboard?
- A An arc-fault circuit interrupter breaker
- B A ground-fault circuit interrupter breaker
- C A Type 1 or Type 2 surge-protective device
- D A Type 3 surge-protective device
Show answer & explanation
Correct: C — A Type 1 or Type 2 surge-protective device
215.18(A) requires an SPD for feeders supplying hotel/motel guest rooms, and 215.18(C) limits it to Type 1 or Type 2. Type 3 SPDs are point-of-utilization devices and don't satisfy this feeder-level requirement; GFCI and AFCI protection address different hazards entirely.
Ground-fault protection of equipment for large feeder disconnects
NEC 215.10 Feeder disconnects rated 1000 A or more on solidly grounded wye systems over 150V to ground (like 480Y/277V) need GFPE per 230.95, unless an exception applies.
Q6 NEC 215.10
A feeder disconnect rated 1200 A supplies a solidly grounded 480Y/277V system. Under 215.10, what does this installation require?
- A Ground-fault protection only if the disconnect is located outdoors
- B No ground-fault protection, since 215.10 only governs services
- C Ground-fault protection of equipment in accordance with 517.17
- D Ground-fault protection of equipment in accordance with 230.95
Show answer & explanation
Correct: D — Ground-fault protection of equipment in accordance with 230.95
215.10 requires GFPE for feeder disconnects rated 1000A or more on solidly grounded wye systems over 150V to ground and not exceeding 1000V phase-to-phase — 480Y/277V fits. The 517.17 reference only substitutes for health care occupancies, and this rule explicitly covers feeders, not just services (215.10).
Identifying feeder conductors (grounded, EGC, ungrounded, multi-system)
NEC 215.12 Feeder grounded conductors follow 200.6 and equipment grounding conductors follow 250.119, while ungrounded conductors need extra phase, system, or polarity marking on multi-system and DC feeders.
Q7 NEC 215.12
A commercial building has feeders supplied from two different nominal voltage systems. Per 215.12(C)(1), what must happen at each termination, connection, and splice point?
- A Each grounded conductor must be re-identified with a different color per system
- B Only the equipment grounding conductor needs additional marking
- C Each ungrounded conductor must be identified by phase and system
- D No additional identification is required if all conduit is labeled
Show answer & explanation
Correct: C — Each ungrounded conductor must be identified by phase and system
215.12(C)(1) requires each ungrounded conductor of a feeder to be identified by phase or line and system at every termination, connection, and splice point when feeders serve more than one nominal voltage system. Grounded conductor identification is a separate rule (215.12(A)), and equipment grounding conductor marking is likewise separate (215.12(B)) — neither substitutes for the ungrounded-conductor phase/system marking this rule requires.
Sizing feeder conductors: minimum ampacity and continuous loads
NEC 215.2 Size feeder conductors to the larger of the 125%-continuous-load calculation and the ampacity left after 310.14 adjustment or correction factors — never just one.
Q8 NEC 215.2
A feeder supplies a mix of continuous and noncontinuous loads, and the equipment is not listed for 100% continuous operation. Per 215.2(A)(1), how must the minimum feeder conductor ampacity be determined?
- A Not less than 125 percent of the sum of all loads
- B Not less than 100 percent of the sum of all loads
- C Not less than the continuous load plus 125 percent of the noncontinuous load
- D Not less than the noncontinuous load plus 125 percent of the continuous load
Show answer & explanation
Correct: D — Not less than the noncontinuous load plus 125 percent of the continuous load
215.2(A)(1) requires ampacity not less than the noncontinuous load plus 125 percent of the continuous load. The 100-percent-of-sum option only applies when the assembly and OCPD are listed for 100 percent continuous operation, and applying 125 percent to the entire load or swapping which load gets the multiplier both misstate the rule.
Overcurrent protection sizing for feeders
NEC 215.3 Size a feeder's overcurrent device for the noncontinuous load plus 125% of the continuous load, unless the whole assembly is listed for 100% operation.
Q9 NEC 215.3
A feeder supplies a mix of continuous and noncontinuous loads, and the overcurrent device is a standard (non-100%-rated) breaker. Per 215.3, how must it be rated at minimum?
- A Not less than the noncontinuous load plus 125% of the continuous load
- B Not less than 80% of the total connected load
- C Not less than the sum of the continuous and noncontinuous loads with no multiplier
- D Not less than 125% of the sum of the continuous and noncontinuous loads
Show answer & explanation
Correct: A — Not less than the noncontinuous load plus 125% of the continuous load
215.3 requires the noncontinuous load plus 125% of the continuous load. Applying 125% to the whole sum over-sizes the device beyond what the rule requires. The plain sum with no multiplier only applies under the 100%-rated-assembly exception, which isn't the case here. The 80% figure is an unrelated cord-and-plug load cap, not a feeder OCPD rule.
Autotransformer-derived feeders and grounded-conductor rules
NEC 215.11 Autotransformer-fed feeders need a grounded-conductor tie to the source system, unless it's a 208/240-volt swap or a qualified, supervised 480/600-volt industrial installation.
Q10 NEC 215.11
Under 215.11, when may a feeder be derived from an autotransformer with no grounded-conductor connection back to the supply system, regardless of occupancy type?
- A When the installation is inspected annually by a licensed electrician
- B When transforming from nominal 208 volts to 240 volts, or 240 volts to 208 volts
- C When the feeder serves only lighting loads
- D When the autotransformer is a dry-type unit rated for indoor use
Show answer & explanation
Correct: B — When transforming from nominal 208 volts to 240 volts, or 240 volts to 208 volts
215.11 permits skipping the grounded-conductor connection for the 208-to-240-volt (or 240-to-208-volt) transformation in any occupancy. Annual inspection, lighting-only loads, and dry-type construction are not conditions this section recognizes as exceptions.
Barriers to prevent contact with energized feeder-tap terminations
NEC 215.15 An open disconnect doesn't mean a dead bus — barriers must block contact with the still-energized busbar or terminal fed by tap conductors.
Q11 NEC 215.15 Code lookup
A crew is landing conductors in a switchgear lineup fed by a feeder tap made under 240.21(B), with the tap's disconnect racked open. Which section requires barriers so no exposed energized busbar or terminal can be inadvertently contacted while they work on the load terminations?
- A 215.10
- B 215.9
- C 215.15
- D 215.18(B)
Show answer & explanation
Correct: C — 215.15
215.15 specifically mandates barriers to prevent inadvertent contact with exposed energized busbars or terminals when servicing load terminations supplied by feeder taps or transformer secondary conductors with the disconnect open. 215.10 covers ground-fault protection of equipment and 215.9 covers GFCI protection for personnel — neither addresses physical barriers for termination work.
Sharing a common neutral across multiple feeders
NEC 215.4 Up to three 3-wire feeders or two 4-wire/5-wire feeders can share one common neutral, but every conductor involved must stay together in the same metal raceway or enclosure.
Q12 NEC 215.4
Which combination of feeders sharing one common neutral conductor is permitted under 215.4(A)?
- A Three sets of 4-wire feeders
- B Two sets of 5-wire feeders
- C Four sets of 3-wire feeders
- D Three sets of 5-wire feeders
Show answer & explanation
Correct: B — Two sets of 5-wire feeders
215.4(A) caps 3-wire feeders sharing a common neutral at three sets, and caps 4-wire or 5-wire feeders sharing a common neutral at two sets. Two sets of 5-wire feeders fits that two-set limit; four sets of 3-wire feeders exceeds the three-set limit, and three sets of 4-wire or 5-wire feeders exceeds the two-set limit.
Feeder equipment grounding conductor requirement
NEC 215.6 If the branch circuits a feeder supplies require an equipment grounding conductor, the feeder must include or provide one for those EGCs to connect to.
Q13 NEC 215.6
A feeder supplies several branch circuits, all of which require equipment grounding conductors. What does 215.6 require of the feeder?
- A The feeder is exempt from any equipment grounding conductor requirement since the branch circuits already have their own
- B The feeder must include or provide an equipment grounding conductor to which the branch-circuit equipment grounding conductors connect
- C The feeder needs an equipment grounding conductor only if any branch circuit is rated over 20 amperes
- D The feeder may rely on its grounded (neutral) conductor to serve as the equipment ground path
Show answer & explanation
Correct: B — The feeder must include or provide an equipment grounding conductor to which the branch-circuit equipment grounding conductors connect
215.6 requires that where a feeder supplies branch circuits needing equipment grounding conductors, the feeder itself must include or provide one, and the branch-circuit equipment grounding conductors connect to it. Using the grounded conductor as a ground path or treating the branch circuits' own EGCs as sufficient on their own misreads the rule, and there is no ampere-rating threshold in 215.6.
SPD baseline requirements: listing, operation indication, and SCCR
NEC 242.6 Every SPD must be listed, show it's working, and carry a short-circuit current rating that exceeds available fault current at its install point.
Q14 NEC 242.6
Which of the following is a baseline requirement for ALL surge protective devices under Article 242?
- A The SPD must include a disconnecting means separate from the overcurrent device
- B The SPD must be installed within 10 ft of the service disconnect
- C The SPD must be a listed device
- D The SPD must be reset manually after each surge event
Show answer & explanation
Correct: C — The SPD must be a listed device
242.6 requires that an SPD be a listed device. Location relative to the service disconnect, manual reset, and a separate disconnecting means are not baseline requirements found in these sections.
SPD grounding connection scheme and compliance
NEC 242.30 An SPD can connect between any two conductors, but it can only bridge grounded and equipment grounding conductors during a surge — never as a permanent connection.
Q15 NEC 242.30
According to 242.30, when may the grounded conductor and the equipment grounding conductor be interconnected through an SPD?
- A Only in healthcare occupancies with isolated grounding systems
- B Only through the SPD's normal operation during a surge
- C Only if a licensed inspector approves the bonding jumper
- D At any time, since SPDs are permitted to bond the two conductors permanently
Show answer & explanation
Correct: B — Only through the SPD's normal operation during a surge
242.30 permits an SPD to connect between any two conductors, but specifically states the grounded conductor and equipment grounding conductor shall be interconnected only by the normal operation of the SPD during a surge — not as a permanent bond. The inspector-approval and healthcare-specific options aren't conditions found in 242.30.
Surge arrester voltage rating and where it can't be used
NEC 242.42 A surge arrester's rating must be at least 125% of the system's maximum continuous operating voltage, and it can never be rated below the actual phase-to-ground voltage at its point of application.
Q16 NEC 242.42
Per 242.42, a surge arrester's duty-cycle rating must be at least what percentage of the maximum continuous operating voltage at the point of application?
- A 100 percent
- B 110 percent
- C 150 percent
- D 125 percent
Show answer & explanation
Correct: D — 125 percent
242.42 requires the duty-cycle rating to be not less than 125 percent of the maximum continuous operating voltage available at the point of application. Rating at only 100 percent (matching 242.40's bare minimum for phase-to-ground voltage) or 110 percent leaves insufficient margin; 150 percent overstates the code minimum.
Interconnecting surge arrester ground to secondary via metal connection
NEC 242.54(A) A metal interconnection between a surge arrester ground and the secondary grounded conductor is only allowed when the secondary already has a qualifying multi-point ground — a water pipe network or a multigrounded neutral system.
Q17 NEC 242.54(A)
A transformer's surge arrester is being metal-interconnected to the secondary grounded conductor under 242.54(A). What must also be true?
- A The secondary conductor must be reduced to a minimum 6 AWG copper size
- B The connection must comply with 242.54(A)(1) or (A)(2)
- C The interconnection must be made only at the service disconnect
- D The arrester must be bonded to the equipment grounding conductor of the load instead
Show answer & explanation
Correct: B — The connection must comply with 242.54(A)(1) or (A)(2)
Per 242.54(A), a metal interconnection to the secondary grounded circuit conductor or grounding electrode conductor is only permitted, in addition to the direct grounding connection at the surge arrester, if the connection also complies with 242.54(A)(1) or (A)(2). The other choices describe requirements not found in this section.
Interconnecting surge arrester ground via spark gap device
NEC 242.54(B) When you can't bond the arrester ground directly per 242.54(A), a spark gap or listed device bridges it — with a breakdown voltage set by whether the primary is ungrounded/unigrounded or multigrounded neutral.
Q18 NEC 242.54(B)
A surge arrester's grounding electrode conductor is not connected per 242.54(A). What does 242.54(B) require as the interconnection method?
- A A spark gap or listed device meeting 242.54(B)(1) or (B)(2)
- B An isolation transformer between the primary and secondary grounding systems
- C A direct bolted bond to the service grounding electrode with no additional device
- D A ground-fault circuit interrupter installed ahead of the arrester
Show answer & explanation
Correct: A — A spark gap or listed device meeting 242.54(B)(1) or (B)(2)
242.54(B) requires the interconnection be made through a spark gap or listed device as required by 242.54(B)(1) or (B)(2). A direct bolted bond is exactly what 242.54(A) covers and is not the case addressed here; an isolation transformer and a GFCI are not recognized substitutes under this section.
How many surge arresters and where to place them
NEC 242.44 Put one surge arrester on every ungrounded conductor, and keep it away from unqualified persons unless it's listed for accessible locations.
Q19 NEC 242.44
A surge arrester is installed in a location accessible to unqualified persons. Under 242.46, what must be true for this installation to comply?
- A The surge arrester must be installed outdoors only
- B The surge arrester must be listed for installation in accessible locations
- C The surge arrester must be mounted at least 8 ft above grade
- D The surge arrester must be within sight of the service equipment
Show answer & explanation
Correct: B — The surge arrester must be listed for installation in accessible locations
242.46 requires surge arresters to be inaccessible to unqualified persons unless listed for installation in accessible locations. There's no outdoor-only requirement, no line-of-sight requirement to service equipment, and no 8 ft mounting height specified in this section.
Type 2 SPD connection points by supply arrangement
NEC 242.14 A Type 2 SPD always connects on the load side of the first overcurrent device — whether that device is the service disconnect, the feeder's building disconnect, or an SDS main.
Q20 NEC 242.14 Code lookup
A commercial building receives its power directly from a utility service, and the design calls for a Type 2 SPD tied into the service equipment. Aside from the exception tied to certain listed service disconnects, which section specifies where this SPD may be connected?
- A 242.14(B)
- B 242.14(A)
- C 242.13(B)
- D 242.14(C)
Show answer & explanation
Correct: B — 242.14(A)
242.14(A) governs Type 2 SPD placement for a service-supplied building or structure, requiring connection on the load side of the service disconnect overcurrent device. 242.14(B) covers feeder-supplied buildings instead, and 242.13(B) addresses Type 1 SPDs at the service, not Type 2.
SPD conductor routing and minimum sizing
NEC 242.24 SPD leads to the line and to ground must be as short and straight as possible, and never smaller than 14 AWG copper or 12 AWG aluminum.
Q21 NEC 242.24
An installer runs the grounding conductor for an SPD in a long loop with several sharp bends to reach a convenient ground bar. Does this comply with 242.24?
- A Yes, as long as the conductor is sized at least 14 AWG copper
- B No, but only because the ground bar is not the nearest available grounding point
- C Yes, because 242.24 only restricts the line-side conductor, not the grounding conductor
- D No, because the conductor must be no longer than necessary and must avoid unnecessary bends
Show answer & explanation
Correct: D — No, because the conductor must be no longer than necessary and must avoid unnecessary bends
242.24 applies to conductors to the line or bus and to ground alike, requiring both to be no longer than necessary and to avoid unnecessary bends. Meeting the minimum size in 242.28 does not satisfy the separate routing requirement in 242.24, and the rule is not limited to the line-side conductor.
How many SPDs and where they may be located
NEC 242.20 An SPD connects to every ungrounded conductor at the point it's applied, and it can go indoors or outdoors as long as unqualified persons can't get at it unless it's listed for that.
Q22 NEC 242.20 Code lookup
A designer is specifying a Type 2 SPD to be installed at a panelboard fed from a 3-phase, 4-wire feeder with a grounded (neutral) conductor. To determine how many ungrounded conductors must have an SPD connection, which section applies?
- A 242.30
- B 242.22
- C 242.28
- D 242.20
Show answer & explanation
Correct: D — 242.20
242.20 states the SPD must be connected to each ungrounded conductor at the point of use, which is the rule that answers a 'how many SPD connections are required' question. 242.28 covers conductor sizing and 242.30 covers the connection between conductors, not the count required.
Feeder/branch-circuit overcurrent protection: location, device, coordination
NEC 245.26(A) Overcurrent protection normally sits at the supply point, and whatever device is used must be proven — by fault-current study and coordination with the conductor's damage curve — to clear a short before the conductor is damaged.
Q23 NEC 245.26(A)
Under 245.26(A), where is overcurrent protection for a feeder's ungrounded conductors required by default?
- A At any accessible point selected by the installing electrician
- B At the midpoint of the conductor run, regardless of engineering analysis
- C At the load end of the conductor, nearest the connected equipment
- D At the point where the conductor receives its supply
Show answer & explanation
Correct: D — At the point where the conductor receives its supply
245.26(A) requires overcurrent protection in each ungrounded conductor at the point where it receives its supply. An alternative location is permitted only when designed under engineering supervision with fault studies and time-current coordination — it isn't left to the installer's discretion or automatically placed at the load end or midpoint.
High-voltage circuit breakers: mounting, ratings, nameplate
NEC 245.21(A) An HV circuit breaker needs five ratings on its nameplate — continuous, interrupting, closing, momentary, and max voltage — each sized to meet or exceed what the system can throw at it.
Q24 NEC 245.21(A)
An indoor high-voltage circuit breaker is being installed in an area that is not metal-enclosed and not a fire-resistant cell-mounted unit. Under what condition is this open-mounted arrangement permitted?
- A The location is accessible to qualified persons only
- B Only if the breaker is rated 600V or less
- C Only if a mechanical position indicator is installed
- D Only if the breaker has a momentary rating exceeding the fault current
Show answer & explanation
Correct: A — The location is accessible to qualified persons only
Per 245.21(A)(1)(a), indoor circuit breakers must be in metal-enclosed or fire-resistant cell-mounted units, or open-mounted in locations accessible to qualified persons only. Voltage rating, position indicators, and momentary rating are separate requirements under other subsections and don't substitute for restricted access.
Load-interrupter switches: coordination, ratings, operation
NEC 245.21(E) A load-interrupter switch must be paired with fuses or breakers rated for the fault current and coordinated so both survive a fault together.
Q25 NEC 245.21(E)
A load-interrupter switch is installed on a feeder. What additional protection is required for it to safely handle a fault?
- A Suitable fuses or circuit breakers coordinated with the switch to interrupt available fault current
- B An automatic transfer switch to isolate the fault
- C A separate disconnecting means installed downstream of the switch
- D None — interrupter switches are rated to clear any available fault current alone
Show answer & explanation
Correct: A — Suitable fuses or circuit breakers coordinated with the switch to interrupt available fault current
Per 245.21(E), load-interrupter switches are permitted only if suitable fuses or circuit breakers are used with them to interrupt available fault currents, and the combination must be electrically coordinated. The switch is not itself rated to clear fault current, so 'none' is wrong, and neither a downstream disconnect nor a transfer switch satisfies the coordination requirement.
Expulsion-type distribution cutouts: install, ratings, ID
NEC 245.21(C) Expulsion cutouts are outdoor-only devices that must be safely re-fusable, rated for available fault current and circuit voltage, and clearly labeled on both the cutout body and the fuse link.
Q26 NEC 245.21(C)
An expulsion-type distribution cutout is being specified for a job. Where is it permitted to be installed?
- A Underground in a vault
- B Outdoors, mounted on a structure at a safe clearance height
- C Indoors in a dedicated electrical closet
- D Inside a metal enclosure in a mechanical room
Show answer & explanation
Correct: B — Outdoors, mounted on a structure at a safe clearance height
245.21(C)(1) prohibits distribution cutouts indoors, underground, or in metal enclosures because the fuse exhaust must not endanger persons. 245.21(C)(7) confirms the intended use is outdoor structure mounting with clearance per 110.34(E).
Oil-filled cutouts: ratings, ID, location, enclosure
NEC 245.21(D) An oil-filled cutout must be rated for continuous current, fault current, voltage, and fault closing, mounted no higher than 5 ft, and clearly labeled.
Q27 NEC 245.21(D)
When sizing the interrupting rating of an oil-filled cutout, what must be included in the available fault current calculation?
- A Only the continuous load current at the cutout
- B Only fault current contributed by connected motors
- C Contributions from all connected sources of energy
- D Only the fault current from the nearest utility source
Show answer & explanation
Correct: C — Contributions from all connected sources of energy
Per 245.21(D)(2), the interrupting rating must not be less than the available fault current the cutout is required to interrupt, including contributions from all connected sources of energy — not just one source or the continuous load current, which is a separate rating under 245.21(D)(1).