Frequently Asked Code Questions
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NEC Questions and Answers - Based on 2011 NEC®
Note: These questions are based on the 2014 NEC®. The underlined text indicates a change to the Code rule for the 2014 NEC.
Q1. What are the Code requirements for marking of electrical equipment?
A1. The manufacturer’s name, trademark, or other descriptive marking must be placed on all electrical equipment and, where required by the Code, markings such as voltage, current, wattage, or other ratings must be provided. All marking must have sufficient durability to withstand the environment involved [110.21].
Where caution, warning, or danger signs or labels are required, the labels must meet the following [110.21(B)]:
- The markings must use words, colors, or symbols that effectively warn personnel [110.21(B)(1)].
Note: ANSI Z535.4, Product Safety Signs and Labels, provides guidelines for the design and durability of signs and labels.
- The label can’t be handwritten, and it must be permanently affixed to the equipment [110.21(B)(2)].
Ex to (2): Labels that contain information that’s likely to change can be handwritten, if it’s legible.
- A permanently affixed sign would include a sticker, but not a piece of paper taped to the equipment.
- The marking must be of sufficient durability to withstand the environment involved [110.21(B)(3)].
Q2. When the Code requires lockable disconnecting means, what does this mean?
A2. Where the Code requires that a disconnecting means is lockable in the open position, the provisions for locking must remain in place whether the lock is installed or not. [110.25]
Exception: Locking provisions for cord-and-plug connected equipment don’t need to remain in place without the lock installed.
Q3. What are the NEC requirements for entrance and egress from electrical equipment working spaces?
A3. At least one entrance of sufficient area
must provide access to and egress from the working space [110.26(C)(1)].
An entrance to and egress from each end of the working space of electrical equipment rated 1,200A or more that’s over 6 ft wide is required. The opening must be a minimum of 24 in. wide and 6½ ft high. A single entrance to and egress from the required working space is permitted where either of the following conditions is met [110.26(C)(2)]:
- Only one entrance is required where the location permits a continuous and unobstructed way of egress travel [110.26(C)(2)(a)].
- Only one entrance is required where the required working space depth is doubled, and the equipment is located so the edge of the entrance is no closer than the required working space distance [110.26(C)(2)(b).
If equipment with overcurrent or switching devices rated 800A or more is installed, personnel door(s) for entrance to and egress from the working space located less than 25 ft from the nearest edge of the working space must have the door(s) open in the direction of egress and be equipped with listed panic hardware [110.26(C)(3).
- History has shown that electricians who suffer burns on their hands in electrical arc flash or arc blast events often can’t open doors equipped with knobs that must be turned.
- Since this requirement is in the NEC, the electrical contractor is responsible for ensuring that panic hardware is installed where required. Some electrical contractors are offended at being held liable for nonelectrical responsibilities, but this rule is designed to save the lives of electricians. For this and other reasons, many construction professionals routinely hold “pre-construction” or “pre-con” meetings to review potential opportunities for miscommunication—before the work begins.
Q4. When multiple branch circuits are present in an enclosure, what does the Code require in regard to grouping of neutral conductors?
A4. The ungrounded and neutral conductors of multiple branch circuits must be grouped together by cable ties or similar means in every enclosure [200.4(B)].
Ex 1: Grouping isn’t required where the circuit conductors are contained in a single raceway or cable unique to that circuit that makes the grouping obvious.
Ex 2: Grouping isn’t required if the conductors pass through a box or conduit body without any splices or terminations, or if the conductors don’t have a loop as described in 314.16(B)(1).
- 210.4(D) contains a similar requirement for branch circuit conductors.
Q5. What is the Code rule regarding the grouping of the conductors of multiwire branch circuits?
A5. The ungrounded and neutral conductors of a multiwire branch circuit must be grouped together by cable ties or similar means at the point of origination [210.4(D)].
Ex: Grouping isn’t required where the circuit conductors are contained in a single raceway or cable unique to that circuit that makes the grouping obvious, or if the conductors have circuit number tags on them.
- Grouping all associated conductors of a multiwire branch circuit together by cable ties or other means within the point of origination makes it easier to visually identify the conductors of the multiwire branch circuit. The grouping will assist in making sure that the correct neutral is used at junction points and in connecting multiwire branch-circuit conductors to circuit breakers correctly, particularly where twin breakers are used. If proper diligence isn’t exercised when making these connections, two circuit conductors can be accidentally connected to the same phase or line.
Caution: If the ungrounded conductors of a multiwire circuit aren’t terminated to different phases or lines, the currents on the neutral conductor won’t cancel, which can cause an overload on the neutral conductor.
Q1. What does the Code require for overcurrent
protection sizing for a single motor-compressor air-conditioner? Please
provide an example.
A1. The short-circuit and ground-fault protective device for single motor-compressors must not be more than 175 percent of the motor-compressor current rating. If the protective device sized at 175 percent isn’t capable of carrying the starting current of the motor-compressor, the next size larger protective device can be used, but in no case can it exceed 225 percent of the motor-compressor current rating [440.22(A)].
Question: What size conductor and
protection are required for a 24A motor-compressor connected to a 240V
(a) 10 AWG, 40A (b) 10 AWG, 60A (c) a or b (d) 10 AWG, 90A
Answer: (a) 10 AWG, 40A
Step 1: Determine the branch-circuit conductor [Table 310.15(B)(16) and 440.32]:
24A x 1.25 = 30A, 10 AWG, rated 30A at 75°C [Table 310.15(B)(16)]
Step 2: Determine the branch-circuit protection [240.6(A) and 440.22(A)]:
24A x 1.75 = 42A, next size down = 40A
If the 40A short-circuit and ground-fault protective device isn’t capable of carrying the starting current, then the protective device can be sized up to 225 percent of the equipment load current rating. 24A x 2.25 = 54A, next size down 50A
Q2. What is the Code rule regarding disconnects on the
primary side of transformers?
A2. A disconnect is required to disconnect all transformer ungrounded primary conductors. The disconnect must be located within sight of the transformer, unless the location of the disconnect is field-marked on the transformer and the disconnect is lockable [450.14].
Author’s Comment: Within sight means that it’s visible and not more than 50 ft from one to the other [Article 100].
Q3. Does the NEC require transformers to be accessible?
A3. Transformers must be readily accessible to qualified personnel for inspection and maintenance, except as permitted by 450.13 (A) or (B) [450.13]:
- Dry-type transformers can be located in the open on walls, columns, or structures [450.13(A)].
- Dry-type transformers, rated not more than 50 kVA, are permitted above suspended ceilings or in hollow spaces of buildings, if not permanently closed in by the structure [450.13(B)].
Author’s Comment: Dry-type transformers not exceeding 50 kVA with a metal enclosure can be installed above a suspended-ceiling space used for environmental air-handling purposes (plenum) [300.22(C)(3)].
Q4. How do I calculate the minimum size of conductor
required by the NEC for a single motor in a continuous duty application?
Please give an example.
A4. Conductors to a single motor must be sized not less than 125 percent of the motor FLC rating as listed in Table 430.247 Direct-Current Motors, Table 430.248 Single-Phase Motors, or Table 430.250 Three-Phase Motors [430.22].
Question: What size branch-circuit conductor is required
for a 7½ hp, 230V, three-phase motor?
(a) 14 AWG (b) 12 AWG (c) 10 AWG (d) 8 AWG
Answer: (c) 10 AWG
Motor FLC = 22A [Table 430.250]
Conductor’s Size = 22A x 1.25
Conductor’s Size = 27.50A, 10 AWG, rated 30A at 75°C [Table 310.15(B)(16)]
Note: The branch-circuit short-circuit and ground-fault protection device using an inverse time breaker is sized at 60A according to 430.52(C)(1) Ex 1:
Circuit Protection = 22A x 2.50
Circuit Protection = 55A, next size up 60A [240.6(A)]
Circuit conductors that supply several motors must not be sized smaller than the sum of the following [430.24]:
(1) 125 percent of the full-load current of the highest rated motor
(2) The full-load current ratings of other motors
Question: What size feeder conductor is required for two 7½
hp, 230V, three-phase motors, if the terminals are rated for 75°C?
(a) 14 AWG (b) 12 AWG (c) 10 AWG (d) 8 AWG
Answer: (d) 8 AWG
Motor FLC = 22A [Table 430.250]
Motor Feeder Conductor = (22A x 1.25) + 22A
Motor Feeder Conductor = 49.50A, 8 AWG rated 50A at 75°C [Table 310.15(B)(16)]
Author’s Comment: The feeder
overcurrent device (inverse time circuit breaker) must comply with
430.62 as follows:
Step 1: Determine the largest branch-circuit overcurrent device rating [240.6(A) and 430.52(C)(1) Ex 1]:
22A x 2.50 = 55A, next size up 60A
Step 2: Size the feeder overcurrent device in accordance with 240.6(A) and 430.62:
Feeder Inverse Time Breaker: 60A + 22A = 82A, next size down, 80A
Author’s Comment: The “next size up protection” rule for branch circuits [430.52(C)(1) Ex 1] doesn’t apply to motor feeder short-circuit and ground-fault protection device sizing.
Q5. What is the Code requirement for disconnecting
means of electric space heating equipment?
A5. Means must be provided to simultaneously disconnect the heater, motor controller, and supplementary overcurrent devices of all fixed electric space-heating equipment from all ungrounded conductors [424.19].
The disconnecting means must be capable of being locked in the open position. The provision for locking or adding a lock to the disconnecting means must be on the switch or circuit breaker, and it must remain in place with or without the lock installed.
The disconnecting means for fixed electric space-heating equipment with supplementary overcurrent protection must be within sight from the supplementary overcurrent devices [424.19(A)].
Author’s Comment: According to Article 100, within sight means that it’s visible and not more than 50 ft from one to the other.
For fixed electric space-heating equipment without supplementary overcurrent protection, the branch-circuit circuit breaker is permitted to serve as the disconnecting means if the circuit breaker is within sight from the heater or it’s capable of being locked in the open position [424.19(B)].
A unit switch with a marked “off” position that’s an integral part of the equipment can serve as the heater disconnecting means, if it disconnects all ungrounded conductors of the circuit [424.19(C)].
Q1. When installing recessed luminaires, what
Code rules must be
A1. Recessed incandescent luminaires must be identified as thermally protected [410.115].
Author’s Comment: When higher-wattage lamps or improper trims are installed, the lampholder contained in a recessed luminaire can overheat, activating the thermal overcurrent device and causing the luminaire to cycle on and off.
Ex 2: Thermal protection isn’t required for recessed Type IC luminaires whose design, construction, and thermal performance characteristics are equivalent to a thermally protected luminaire.
Recessed Luminaire must maintain the follow clearances from combustible materials [410.116]:
- A recessed luminaire that isn’t identified for contact with insulation must have all recessed parts, except the points of supports, spaced not less than 1⁄4 in. from combustible materials.
- A Type IC luminaire (identified for contact with insulation) can be in contact with combustible materials.
Thermal insulation must not be installed above a recessed luminaire or within 3 in. of the luminaries’ enclosure, wiring compartment, or ballast, transformer, LED driver, or power supply unless identified for contact with insulation, Type IC.
Fixture wires installed in accordance with Article 402 and protected against overcurrent in accordance with 240.5(B)(2), are permitted to run from the luminaire to an outlet box located at least 1 ft away from the luminaire, as long as the conductors aren’t over 6 ft long [410.117].
Q2. What is the Code
rule regarding disconnecting means for fluorescent luminaires?
A2. In indoor locations, other than dwellings and associated accessory structures, fluorescent luminaires that utilize double-ended lamps (typical fluorescent lamps) and contain ballasts that can be serviced in place must have a disconnecting means [410.130(G)(1)].
For existing installed luminaires, a disconnecting means must be added at the time a ballast is replaced.
Author’s Comment: Changing the ballast while the circuit feeding the luminaire is energized has become a regular practice because a local disconnect isn’t available.
Ex 2: A disconnecting means isn’t required for the emergency illumination required in 700.16.
Ex 3: For cord-and-plug-connected luminaires, an accessible separable connector, or an accessible plug and receptacle, is permitted to serve as the disconnecting means.
Ex 4: A disconnecting means isn’t required in industrial establishments with restricted public access where written procedures and conditions of maintenance and supervision ensure that only qualified persons will service the installation.
Ex 5: If more than one luminaire is installed and is supplied by a branch circuit that isn’t of the multiwire type, a disconnecting means isn’t required for every luminaire; but, only when the light switch for the space ensures that some of the luminaires in the space will still provide illumination.
When connected to multiwire branch circuits, the fluorescent luminaire disconnect must simultaneously break all circuit conductors of the ballast, including the neutral conductor [410.130(G)(2)].
Author’s Comment: This rule requires the disconnecting means to open “all circuit conductors of a multiwire branch circuit,” including the neutral conductor. If the neutral conductor in a multiwire circuit isn’t disconnected at the same time as the ungrounded conductors, a false sense of security can result in an unexpected shock from the neutral conductor.
The fluorescent luminaire disconnecting means must be accessible to qualified persons, and if the disconnecting means is external to the luminaire, it must be a single device and must be located in sight from the luminaire [410.130(G)(3)].
Q3. What does the Code
require in regard to the identification and termination of a “wild leg”
in a panelboard?
A3. Panelboards supplied by a 4-wire, delta-connected, three-phase (high-leg) system must have the high-leg conductor (which operates at 208V to ground) terminate to the “B” phase of the panelboard [408.3(E)].
Ex: The high-leg conductor can terminate to the “C” phase when the meter is located in the same section of a switchboard or panelboard.
Note: Orange identification, or some other effective means, is required for the high-leg conductor [110.15 and 230.56].
Warning: The ANSI standard for meter equipment requires the high-leg conductor (208V to neutral) to terminate on the “C” (right) phase of the meter socket enclosure. This is because the demand meter needs 120V and it gets it from the “B” phase.
WARNING: When replacing equipment in existing facilities that contain a high-leg conductor, use care to ensure that the high-leg conductor is replaced in the original location. Prior to 1975, the high-leg conductor was required to terminate on the “C” phase of panelboards and switchboards. Failure to re-terminate the high leg in accordance with the existing installation can result in 120V circuits being inadvertently connected to the 208V high leg, with disastrous results.
Q4. Does the NEC
include a minimum and maximum height for switches or circuit breakers?
A4. Switches and circuit breakers used as switches must be capable of being operated from a readily accessible location. They must also be installed so the center of the grip of the operating handle of the switch or circuit breaker, when in its highest position, isn’t more than 6 ft 7 in. above the floor or working platform [240.24(A) and 404.8(A)].
Author’s Comment: The disconnecting means for a mobile home must be installed so the bottom of the enclosure isn’t less than 2 ft above the finished grade or working platform [550.32(F)].
Ex 1: On busways, fusible switches and circuit breakers can be located at the same level as the busway where suitable means is provided to operate the handle of the device from the floor.
Ex 2: Switches and circuit breakers used as switches can be mounted above 6 ft 7 in. if they’re next to the equipment they supply, and are accessible by portable means [240.24(A)(4)].
Q5. Does the Code
allow range hoods to be cord-and-plug connected?
A5. Range hoods can be cord-and-plug-connected if all of the following conditions are met [422.16(B)(4)]:
- The flexible cord terminates with a grounding-type attachment plug.
- The length of the cord must not be less than 18 in. or longer than 36 in.
- The range hood receptacle must be located to avoid physical damage to the flexible cord.
- The range hood receptacle must be accessible.
- The range hood receptacle must be supplied by an individual branch circuit.
Author’s Comment: An above the range microwave that contains a fan listed as a range hood must comply with this section, if it’s cord-and-plug-connected.
By Mike Holt for EC&M Magazine
Q1. What are the Code rules for luminaires installed in bathtub and shower areas?
A1. According to 410.10(D), no part of chain-, cable-, or cord-suspended luminaires, track luminaires, or ceiling paddle fans can be located within 3 ft horizontally and 8 ft vertically from the top of the bathtub rim or shower stall threshold.
Author’s Comment: See 404.4 for
switch requirements and 406.9(C) for receptacle requirements within or
near bathtubs or shower stalls.
Luminaires located within the actual outside dimensions of a bathtub or shower to a height of 8 ft from the top of the bathtub rim or shower threshold must be marked for damp locations. If subject to shower spray, the luminaires must be marked for wet locations.
Q2. What are the NEC rules regarding poles used to support luminaires?
A2. A pole can be used to support luminaires, and can be used as a raceway [410.30].
Author’s Comment: With security being a high priority, many owners want to install security cameras on existing parking lot poles. However, 820.133(A)(1)(b) prohibits the mixing of power and communications conductors in the same raceway.
In addition, they must comply with the following six
(1) The pole must have an accessible 2 in. x 4 in. handhole with a cover suitable for use in wet locations that provides access to the supply conductors within the pole.
Ex 1: The handhole isn’t required for a pole that’s 8 ft or less in height, if the supply conductors for the luminaire are accessible by removing the luminaire.
Ex 2: The handhole can be omitted on poles that are 20 ft or less in height, if the pole is provided with a hinged base.
(2) When the supply raceway or cable doesn’t enter the pole, a threaded fitting or nipple must be welded, brazed, or attached to the pole opposite the handhole opening for the supply conductors.
(3) A metal pole must
have an equipment grounding terminal accessible from the handhole.
Ex: A grounding terminal isn’t required in a pole that’s 8 ft or less in height above grade if the splices are accessible by removing the luminaire.
(5) Metal poles used for the support of luminaires must be connected to an equipment grounding conductor of a type recognized in 250.118 [250.4(A)(5)].
DANGER: Because the contact resistance of an electrode to the earth is so high, very little fault current returns to the power supply if the earth is the only fault current return path. Result—the circuit overcurrent device won’t open and clear the ground fault, and the metal pole will become and remain energized by the circuit voltage.
(6) Conductors in vertical metal poles must be supported when the vertical rise exceeds 100 ft [Table 300.19(A)].
Author’s Comment: When provided by the manufacturer of roadway lighting poles, so-called J-hooks must be used to support conductors, as they’re part of the listing instructions [110.3(B)].
Q3. What does the Code require regarding Track Lighting installation?
A3. Track lighting must be permanently installed and permanently connected to the branch-circuit wiring [410.151(A)]. Lampholders for track lighting are designed for lamps only, so a receptacle adapter isn’t permitted [410.90].
The connected load on a lighting track must not exceed the rating of the track, and an overcurrent device whose rating exceeds the rating of the track must not supply the track [410.151(B)].
Note: The feeder or service load calculations of 220.43(B) don’t limit the number of feet of track on a circuit, nor do they limit the number of luminaires mounted on an individual track.
Track lighting must not be installed [410.151(C)]:
- If it’s likely to be subjected to physical damage.
- In wet or damp locations.
- If subject to corrosive vapors.
- In storage battery rooms.
- In any hazardous location.
- If concealed.
- If extended through walls, partitions, or floors.
- Less than 5 ft above the finished floor, except where protected from physical damage or where the track operates below 30V open-circuit voltage.
- Within 3 ft horizontally and 8 ft vertically from the top of a bathtub rim or shower space [410.4(D)].
Track lighting must be securely mounted to support the weight of the luminaires. A single track section 4 ft or shorter in length must have two supports, and, where installed in a continuous row, each individual track section of not more than 4 ft in length must have one additional support [410.154].
Q4. What restrictions does the NEC put on the installation of luminaires in commercial cooking hoods?
A4. Luminaires can be installed in commercial cooking hoods if all of the following conditions are met [410.10(C)]:
- The luminaire is identified for use within commercial cooking hoods.
- The luminaire is constructed so that all exhaust vapors, grease, oil, or cooking vapors are excluded from the lamp and wiring compartment.
- The luminaire is corrosion resistant, or protected against corrosion, and the surface must be smooth so as not to collect deposits and to facilitate cleaning.
- Wiring methods and materials supplying the luminaire must not be exposed within the cooking hood.
Author’s Comment: Standard gasketed luminaires must not be installed in a commercial cooking hood because accumulations of grease and oil can result in a fire caused by high temperatures on the glass globe.
Q5. What means of support does the Code allow for luminaires?
A5. Outlet boxes designed for the support of luminaires must be supported by one of the following methods [410.36]:
- Fastened to any surface that provides adequate support [314.23(A)].
- Supported from a structural member of a building or from grade by a metal, plastic, or wood brace [314.23(B)].
- Secured to a finished surface (drywall or plaster walls or ceilings) by clamps, anchors, or fittings identified for the application [314.23(C)].
- Secured to the structural or supporting elements of a suspended ceiling [314.23(D)].
- Supported by two intermediate metal conduits or rigid metal conduits threaded wrenchtight [314.23(E) and (F)].
- Embedded in concrete or masonry [314.23(G)].
- Outlet boxes for luminaires can support a luminaire that weighs up to 50 lb, unless the box is listed for the luminaries’ actual weight [314.27(A)(2)].
If framing members of suspended-ceiling systems are used to support luminaires, they must be securely fastened to each other and they must be securely attached to the building structure at appropriate intervals. Luminaires must be attached to the suspended-ceiling framing members with screws, bolts, rivets, or clips that are listed and identified for such use [410.36(B)].
- The NEC doesn’t require independent support wires for suspended-ceiling luminaires that aren’t installed in a fire-rated ceiling; however, building codes often do.
- Raceways and cables within a suspended ceiling must be supported in accordance with 300.11(A). Outlet boxes can be secured to the ceiling-framing members by bolts, screws, rivets, clips, or independent support wires that are taut and secured at both ends [314.23(D)].
Trees can be used to support luminaires, but they must not be used to support overhead conductor spans [225.26 and 410.36(G)].