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NEC Questions and Answers – Based on the 2011 NEC
August 2012
By Mike Holt for EC&M Magazine
Here’s the follow up to yesterday’s newsletter.This includes all of the answers to the questions sent, so you can see how you did.
Q1. Are unlisted communications cables allowed to enter buildings?
A1. Unlisted communications cables can be installed in building spaces other than risers, ducts, or plenum spaces as described in 300.22(C), if the length of the cable within the building from its point of entrance doesn’t exceed 50 ft and the cable terminates in an enclosure or primary protector [800.48].
[800.48 Note 2] The primary protector must be located as close as practicable to the point at which the cable enters the building [800.90(B)]. Therefore, unlisted outside plant communications cables may not be permitted to enter the building if it’s practicable to place the primary protector closer than 50 ft to the point of entrance.
Author’s Comment: The “point of entrance” is defined as the point within the building where the cable emerges from an external wall, from a concrete floor slab, or from rigid metal conduit or intermediate metal conduit connected to an electrode by a grounding conductor in accordance with 800.100 [800.2].
Q2. What is the Code rule for mixing conductors of different systems in the same raceway, cable, or enclosure?
A2. Power conductors of alternating-current and direct-current systems rated 600V or less can occupy the same raceway, cable, or enclosure if all conductors have an insulation voltage rating not less than the maximum circuit voltage [300.3(C)(1)].
Author’s Comments:
• Control, signal, and communications wiring must be separated from power and lighting circuits so the higher-voltage conductors don’t accidentally energize the control, signal, or communications wiring:
– CATV Coaxial Cable, 820.133(A)
– Class 1, 725.48
– Class 2, and Class 3 Control Circuits, 725.136(A)
– Communications Circuits, 800.133(A)(1)(c)
– Fire Alarm Circuits, 760.136(A)
– Instrumentation Tray Cable, 727.5
- Sound Circuits, 640.9(C)
• Class1 circuit conductors can be installed with associated power conductors [725.48(B)(1)] if all conductors have an insulation voltage rating not less than the maximum circuit voltage [300.3(C)(1)].
• A Class 2 circuit that’s been reclassified as a Class 1 circuit [725.130(A) Ex 2] can be installed with associated power conductors [725.48(B)(1)] if all conductors have an insulation voltage rating not less than the maximum circuit voltage [300.3(C)(1)].
[300.3(C)(1) Note 2] PV system conductors, both direct current and alternating current, are permitted to be installed in the same raceways, outlet and junction boxes, or similar fittings with each other, but they must be kept entirely independent of all other non-PV system wiring [690.4(B)].
Q3. How does the Code address the spread of fire or products of combustion in regard to fire rated assemblies?
A3. Electrical circuits and equipment must be installed in such a way that the spread of fire or products of combustion won’t be substantially increased. Openings into or through fire-rated walls, floors, and ceilings for electrical equipment must be fire-stopped using methods approved by the authority having jurisdiction to maintain the fire-resistance rating of the fire-rated assembly [300.21].
Author’s Comment: Fire-stopping materials are listed for the specific types of wiring methods and the construction of the assembly that they penetrate.
[300.22 Note] Directories of electrical construction materials published by qualified testing laboratories contain listing and installation restrictions necessary to maintain the fire-resistive rating of assemblies. Outlet boxes must have a horizontal separation not less than 24 in. when installed in a fire-rated assembly, unless an outlet box is listed for closer spacing or protected by fire-resistant “putty pads” in accordance with manufacturer’s instructions.
Author’s Comments:
• Boxes installed in fire-resistance-rated assemblies must be listed for the purpose. If steel boxes are used, they must be secured to the framing member, so cut-in type boxes aren’t permitted (UL White Book, Guide Information for Electrical Equipment, www.ul.com/regulators/2008_WhiteBook.pdf).
• This rule also applies to control, signaling, and communications cables or raceways. – CATV, 820.26 – Communications, 800.26 – Control and Signaling, 725.25 – Fire Alarm, 760.3(A) – Optical Fiber, 770.26 – Sound Systems, 640.3(A)
Q4. Where does the Code require a boundary seal when leaving a Class I, Division 2 location and entering an unclassified area?
A4. A raceway seal fitting must be installed in each raceway that passes from a Class I, Division 2 location into an unclassified location within 10 ft of the Class I, Division 2 area on either side of the boundary [501.15(B)(2)].
Rigid metal conduit or threaded steel intermediate metal conduit must be used between the sealing fitting and the point at which the raceway leaves the Division 2 location, and a threaded connection must be used at the sealing fitting. Except for listed reducers at the raceway seal, there must be no union, coupling, box, or fitting between the raceway seal and the point at which the raceway leaves the Division 2 location.
Raceway boundary seals aren’t required to be explosionproof, but must be identified for the purpose of minimizing the passage of gases under normal operating conditions, and they must be accessible.
Author’s Comments:
• See the definition of “Accessible” as it relates to wiring methods.
• The raceway boundary seal at unclassified locations is to minimize the passage of gases or vapors, not to contain explosions in the raceway system.
Ex 1: A raceway boundary seal fitting isn’t required for a raceway that passes through the Class I, Division 2 area unbroken with no fittings less than 1 ft beyond the boundary to an unclassified location.
Ex 2: A raceway boundary seal fitting isn’t required for raceways that terminate at an outdoor unclassified location for cable trays, cablebus, ventilated busways, MI cable, or open wiring.
Ex 3: A boundary seal fitting isn’t required for a raceway that passes from an enclosure or room that’s unclassified as a result of pressurization into a Class I, Division 2 location.
Q5. What are the GFCI protection requirements for a receptacle installed in a non-dwelling location if it is under a counter with a sink above it?
A5. All 15A and 20A, 125V receptacles installed within 6 ft of the outside edge of a sink in non-dwelling occupancies must be GFCI protected [210.8(B)(5)].
Ex 1: In industrial laboratories, receptacles used to supply equipment where removal of power would introduce a greater hazard aren’t required to be GFCI protected.
Ex 2: Receptacles located in patient bed locations of general care or critical care areas of health care facilities aren’t required to be GFCI protected.
Q6. What is the NEC requirement regarding GFCI protection of outlets supplying pool pump motors?
A6. GFCI protection is required for outlets supplying pool pump motors connected to single-phase 120V through 240V branch circuits rated 15A or 20A, whether by receptacle or by direct connection. [680.21(C)]
Q7. What wiring methods are allowed by the Code in spaces above a lay-in ceiling?
A7. Section 300.22(C) applies to spaces used for air-handling purposes, but not fabricated for environmental air-handling purposes. This requirement doesn’t apply to habitable rooms or areas of buildings, the prime purpose of which isn’t air handling.
[300.22(C) Note 1] The spaces above a suspended ceiling or below a raised floor used for environmental air are examples of the type of space to which this section applies.
[300.22(C) Note 2] The phrase “other space used for environmental air (plenum) ” correlates with the term “plenum” in NFPA 90A, Standard for the Installation of Air-Conditioning and Ventilating Systems, and other mechanical codes where the ceiling cavity plenum is used for return air purposes, as well as some other air-handling spaces.
Electrical metallic tubing, rigid metal conduit, intermediate metal conduit, armored cable, metal-clad cable without a nonmetallic cover, and flexible metal conduit can be installed in cavity plenum space. If accessible, surface metal raceways or metal wireways with metal covers can be installed in cavity plenum space [300.22(C)(1)].
Author’s Comments:
• PVC conduit [Article 352], electrical nonmetallic tubing [Article 362], liquidtight flexible conduit, and nonmetallic cables aren’t permitted to be installed in spaces used for environmental air because they give off deadly toxic fumes when burned or superheated.
• Plenum-rated control, signaling, and communications cables and raceways are permitted in a plenum space:
– CATV, 820.179(A)
– Communications, 800.21
– Control and Signaling, 725.154(A)
– Fire Alarm, 760.7
– Optical Fiber Cables and Raceways, 770.113(C)
– Sound Systems, 640.9(C) and 725.154(A)
• Any wiring method suitable for the condition can be used in a space not used for environmental air-handling purposes.
Metal cable tray systems can be installed to support the wiring methods and equipment permitted by this section [300.22(C)(2)(a)].
Electrical equipment with metal enclosures is permitted to be installed in a plenum space [300.22(C)(3)].
Author’s Comment: Examples of electrical equipment permitted in a plenum space would be air-handlers, junction boxes, dry-type transformers; however transformers must not be rated not over 50 kVA when located in hollow spaces [450.13(B)].
Q8. Do the equipotential bonding requirements of Part II of Article 680 apply to storable swimming pools?
A8. No. Electrical installations for storable pools must also comply with Part I of Article 680 [680.30]. They are not required to follow the equipotential bonding requirements of Part II.
Author’s Comment: The requirements contained in Part I of Article 680 include the locations of switches, receptacles, and luminaires.
A storable swimming pool is defined in 680.2 as an aboveground pool with a maximum water depth of 42 in.
Author’s Comment: Storable pools are sold as a complete package that consists of the pool walls, vinyl liner, plumbing kit, and pump/filter device. Underwriters Laboratories, Inc. (UL) requires the pump/filter units to have a minimum 25 ft cord to discourage the use of extension cords.
Q9. What is the Code requirement for an intersystem bonding termination and what is to connect to it?
A9. The Code requires An external accessible intersystem bonding termination for the connection of communications systems bonding conductors must be provided at service equipment or metering equipment enclosure and disconnecting means for buildings or structures supplied by a feeder [250.94]. The intersystem bonding termination must:
(1) Be accessible for connection and inspection.
(2) Consist of a set of terminals with the capacity for connection of not less than three intersystem bonding conductors.
(3) Not interfere with opening the enclosure for a service, building/structure disconnecting means, or metering equipment.
(4) Be securely mounted and electrically connected to service equipment, the meter enclosure, or exposed nonflexible metallic service raceway, or be mounted at one of these enclosures and be connected to the enclosure or grounding electrode conductor with a minimum 6 AWG copper conductor.
(5) Be securely mounted to the building/structure disconnecting means, or be mounted at the disconnecting means and be connected to the metallic enclosure or grounding electrode conductor with a minimum 6 AWG copper conductor.
(6) The terminals must be listed as grounding and bonding equipment.
Author’s Comment: According to Article 100, an intersystem bonding termination is a device that provides a means to connect communications systems grounding and bonding conductors to the building grounding electrode system.
Ex: At existing buildings or structures, an external accessible means for bonding communications systems together can be by the use of a: (1) Nonflexible metallic raceway,
(2) Grounding electrode conductor, or
(3) Connection approved by the authority having jurisdiction.
[250.94 Note 2] Communications systems must be bonded to the intersystem bonding termination in accordance with the following Code requirements:
• Antennas/Satellite Dishes, 810.15 and 810.21
• CATV, 820.100
• Telephone Circuits, 800.100
Author’s Comment: All external communications systems must be connected to the intersystem bonding termination to minimize the damage to them from induced potential (voltage) differences between the systems from a lightning event.
Q10. What are the acceptable wiring methods for Class I locations according to the NEC?
A10. Only the following wiring methods are permitted within a Class I, Division 1 location [501.10(A)(1)].
• Threaded rigid metal conduit or intermediate metal conduit with explosionproof fittings [501.10(A)(1)(a)].
• MI cable terminated with fittings listed for the location [501.10(A)(1)(b)].
• In industrial establishments with restricted public access where only qualified persons will service the installation, MC-HL cable listed for use in Class I, Zone 1, or Division 1 locations, with a gas/vaportight continuous corrugated metallic sheath, an overall jacket of suitable polymeric material, a separate equipment grounding conductor(s) in accordance with 250.122, and terminated with fittings listed for the application. Such cable must comply with Part II of Article 330 [501.10(A)(1)(c)].
Author’s Comment: Article 100 defines a “Qualified Person” as one who has skills and knowledge related to the construction and operation of the equipment and has received safety training on the hazards involved.
• In industrial establishments with restricted public access where only qualified persons will service the installation, ITC-HL cable terminated with fittings listed for the location [501.10(A)(1)(d)].
• Explosionproof flexible metal connection listed for the location are permitted in a Class I, Division 1 location when necessary for vibration, movement, or flexible cords for difficult bends in accordance with 501.140 if terminated with cord connectors listed for the location [501.10(A)(2)].
• Boxes and fittings must be approved by the authority having jurisdiction for Class I, Division 1 locations [501.10(A)(3)].
Only the following wiring methods are permitted within a Class I, Division 2 location [501.10(B)].
• Wiring methods permitted in Class I, Division 1 locations by 501.10(A) [501.10(B)(1)].
• Enclosed gasketed busways and enclosed gasketed wireways.
• PLTC and Type PLTC-ER cable terminated with listed fittings in accordance with Article 725.
• ITC and ITC-ER cable terminated with listed fittings as permitted in 727.4.
• Types MC, MV, or TC cables including installation in cable tray systems and terminated with listed fittings.
• Where metallic conduit doesn’t provide sufficient corrosion resistance, reinforced thermosetting resin conduit and Schedule 80 PVC conduit can be used, but only in industrial establishments where maintenance and supervision ensure that only qualified persons service the installation.
If flexibility is necessary, the following wiring methods are permitted [501.10(B)(2)]:
• Listed flexible metal fittings.
• Flexible metal conduit with listed fittings.
• Liquidtight flexible metal conduit with listed fittings.
• Liquidtight flexible nonmetallic conduit with listed fittings.
• Flexible cords listed for extra-hard usage, containing an equipment grounding conductor, and terminated with listed fittings.
Author’s Comments:
• See the definition of “Grounding Conductor, Equipment” in Article 100.
• If flexible cords are used, they must comply with 501.140.
[501.10(B) Note] See 501.30(B) for equipment grounding requirements where flexible conduit is used.
General-purpose enclosures and fittings are permitted according to 501.10(B)(4) unless the enclosure contains make-and-break contacts for meters, instruments, and relays [501.105(B)(1)], switches, circuit breakers, or motor controllers [501.115(B)(1)], signaling, alarm, remote-control, and communications systems [501.150(B)].
Author’s Comment: See the definition of “Controller” in Article 100. [501.10]
Q11. If a single receptacle is installed behind a washing machine within 6 ft of a laundry tub in a dwelling unit, is GFCI protection required?
A11. GFCI protection is required for all 15A and 20A, 125V receptacles located within an arc measurement of 6 ft from the outside edge of the sink in dwellings and for other than kitchen sinks [210.8(A)(7)].
Q12. Does the rule for GFCI protection of receptacles within 6 ft of a sink apply to undercounter receptacles for dishwashers and kitchen waste disposers in dwellings?
A12. No. GFCI protection is required for all 15A and 20A, 125V receptacles that serve countertop surfaces in a dwelling unit [210.8(A)(6)].
Author’s Comments:
• GFCI protection is required for all receptacles that serve countertop surfaces, but GFCI protection isn’t required for receptacles that serve built-in appliances, such as dishwashers or kitchen waste disposers.
• See 210.52(C) for the location requirements of countertop receptacles.
Q13. Does the Code require the bonding of metal skin on wooden frame “pole buildings”?
A13. Exposed structural metal that forms a metal building frame that’s likely to become energized must be bonded to the [250.104(C)]:
• Service equipment enclosure,
• Service neutral conductor,
• Building/structure disconnecting means for buildings or structures supplied by a feeder or branch circuit,
• Grounding electrode conductor if of sufficient size, or
• Grounding electrode system.
Author’s Comment: This rule doesn’t require the bonding of sheet metal framing members (studs) or the metal skin of a wood frame building.
The bonding jumper must be sized in accordance with Table 250.66, based on the area of the ungrounded supply conductors. The bonding jumper must be copper where within 18 in. of the earth [250.64(A)], securely fastened to the surface on which it’s carried [250.64(B)], and adequately protected if exposed to physical damage [250.64(B)]. In addition, all points of attachment must be accessible, except as permitted in 250.68(A).
Section 250.24(C)(3) addresses bonding of conductive materials in more general terms. Conductive materials such as metal water piping systems, metal sprinkler piping, metal gas piping, and other metal-piping systems, as well as exposed structural steel members likely to become energized must be bonded together in a manner that creates a low-impedance fault current path that’s capable of carrying the maximum fault current likely to be imposed on it [ 250.4(C)(3)].
Author’s Comment: The phrase “likely to become energized” is subject to interpretation by the authority having jurisdiction.
Q14. What are the requirements for SE cable if used for feeders and branch circuits, and what conductor temperature rating is used when sizing the SE cable?
A14. Type SE service-entrance cable is permitted for branch circuits and feeders where the circuit conductors are insulated [338.10(B)(1)].
SE cable is permitted for branch circuits and feeders if the insulated conductors are used for circuit wiring, and the uninsulated conductor is only used for equipment grounding purposes [338.10(B)(2)].
Ex: In existing installations, uninsulated conductors may be used for the neutral conductor if the uninsulated neutral conductor of the cable originates in service equipment.
SE cable must not be subjected to conductor temperatures exceeding its insulation rating [338.10(B)(3)]. SE cable used for branch circuits or feeders must comply with (a) and (b) [338.10(B)(4)].
338.10(B)(1)(a) Interior Installations. SE cable used for interior branch circuit or feeder wiring must be installed in accordance with the same requirements as Type NM Cable—Article 334, excluding 334.80.
The maximum conductor temperature rating can be used [310.15(B)(2)] for ampacity adjustment and correction purposes, but when installed in thermal insulation the conductors must be sized in accordance with Table 310.15(B)(16) 60°C rated conductor column
Caution: Underground service-entrance cable (USE) is not permitted for interior wiring because it does not have a flame-retardant insulation. It would only be permitted in interior wiring when dual listed as wire type in accordance with Table 310.104, such as RHW.
338.10(B)(1)(b) Exterior Installations. The cable must be supported in accordance with 334.30 and where run underground the cable must comply with Part II of Article 340.
Q 15. What method(s) of termination does the Code allow for grounding and bonding conductors?
A15. Equipment grounding conductors, grounding electrode conductors, and bonding jumpers must terminate in one of the following methods [250.8(A)] :
• Listed pressure connectors
• Terminal bars
• Pressure connectors listed for direct burial or concrete encasement [250.70]
• Exothermic welding
• Machine screws that engage at least two threads or are secured with a nut.
• Self-tapping machine screws that engage at least two threads
• Connections that are part of a listed assembly
• Other listed means
Connection devices or fittings that depend solely on solder aren’t allowed [250.8(B )].
For more NEC Practice purchase Mike Holt's NEC Practice Questions book, Based on the 2011 NEC.
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