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Frequently Asked Code Questions

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NEC Questions and Answers - Based on 2011 NEC®

January 2014

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)]:

Note: ANSI Z535.4, Product Safety Signs and Labels, provides guidelines for the design and  durability of signs and labels.

Ex to (2): Labels that contain information that’s likely to change can be handwritten, if it’s legible.

Author’s Comment:

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)]:

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).

Author’s Comment:

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).

Author’s Comment:

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.

Author’s Comment:

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.

December 2013

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 circuit?
(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]:

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)].

October 20113

Q1. When installing recessed luminaires, what Code rules must be followed?
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]:

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)]:

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.


September 2013

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 requirements:
(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)]:

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)]:

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]:

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)].

Author’s Comment:

Trees can be used to support luminaires, but they must not be used to support overhead conductor spans [225.26 and 410.36(G)].