By Mike Holt for EC&M Magazine

Here's the follow up to last Thursday's newsletter. This includes all of the answers to the questions sent, so you can see how you did.

Note: These questions are based on the 2014 NEC®. Any underlined text indicates a change to the Code rule for the 2014 NEC.

Q1. What are the overcurrent protection requirements for panelboards?

A1. Each panelboard must be provided with overcurrent protection located within, or at any point on the supply side of, the panelboard. The overcurrent device must have a rating not greater than that of the panelboard, and it can be located within or on the supply side of the panelboard [408.36] .

Ex 1: Individual overcurrent protection isn’t required for panelboards used as service equipment where the service disconnecting means consists of up to six circuit breakers mounted in a single enclosure in accordance with 230.71.

When a panelboard is supplied from a transformer, as permitted in 240.21(C), the overcurrent protection for the panelboard must be on the secondary side of the transformer. The required overcurrent protection can be in a separate enclosure ahead of the panelboard, or it can be in the panelboard [408.36(B)].

Plug-in circuit breakers that are back-fed from field-installed conductors must be secured in place by an additional fastener that requires other than a pull to release the breaker from the panelboard [408.36(C)].

Author’s Comment:

The purpose of the breaker fastener is to prevent the circuit breaker from being accidentally removed from the panelboard while energized, thereby exposing someone to dangerous voltage.

CAUTION: Circuit breakers marked “Line” and “Load” must be installed in accordance with listing or labeling instructions [110.3(B)]; therefore, these types of devices must not be back-fed.

Q2. What are the conductor sizing requirements as they relate to equipment terminal ratings?

A2. Conductors are to be sized using their ampacity from the insulation temperature rating column of Table 310.15(B)(16) that corresponds to the lowest temperature rating of any terminal, device, or conductor of the circuit [110.14(C)].

Author’s Comment:

Conductors with insulation temperature ratings higher than the termination’s temperature rating can be used for ampacity adjustment, correction, or both.

Unless the equipment is listed and marked otherwise, conductor sizing for equipment terminations must be based on Table 310.15(B)(16) in accordance with 110.14(C)(1) (a) or (b):

Equipment Rated 100A or Less [110.14(C)(1)(a)]:

(1) Conductors must be sized using the 60°C temperature column of Table 310.15(B)(16).

(3) Conductors terminating on terminals rated 75°C are sized in accordance with the ampacities listed in the 75°C temperature column of Table 310.15(B)(16).

(4) Motors marked with design letters B, C, or D, conductors having an insulation rating of 75°C or higher can be used, provided the ampacity of such conductors doesn’t exceed the 75°C ampacity.

Equipment Rated Over 100A [110.14(C)(1)(b)]:.

(1) Conductors must be sized using the 75°C temperature column of Table 310.15(B)(16).

(2) Separate Connector Provisions. Conductors can be sized to the 90°C column of Table 310.15(B)(16) if the conductors and pressure connectors are rated at least 90°C.

Note: Equipment markings or listing information may restrict the sizing and temperature ratings of connected conductors.

Q3. What are the requirements when replacing nongrounding type receptacles?

A3. If an equipment grounding conductor doesn’t exist in the outlet box, the existing nongrounding-type receptacles can be replaced with [406.4(D)(2)]:

(a) A nongrounding-type receptacle.

(b) A GFCI-type receptacle marked “No Equipment Ground.”

(c) A grounding-type receptacle, if GFCI protected and marked “GFCI Protected” and “No Equipment Ground.”

Author’s Comment:

• GFCI protection functions properly on a 2-wire circuit without an equipment grounding conductor because the circuit equipment grounding conductor serves no role in the operation of the GFCI-protection device. See the definition of “Ground-Fault Circuit Interrupter” for more information.

Author's Comment:

If a nongrounding type receptacle is replaced with a AFCI or GFCI type receptacle, they must be located in a readily accessible location.

 

CAUTION: The permission to replace nongrounding-type receptacles with GFCI-protected grounding-
type receptacles doesn’t apply to new receptacle outlets that extend from an existing outlet box that’s not connected to an equipment grounding conductor. Once you add a receptacle outlet (branch-circuit extension), the receptacle must be of the grounding type and it must have its grounding terminal connected to an equipment grounding conductor of a type recognized in 250.118, in accordance with 250.130(C).

Q4. When installing outside branch circuits and feeders, what is the minimum vertical clearance required for overhead conductors?

A4. Overhead conductor spans must maintain vertical clearances as follows [225.18]:

(1) 10 ft above finished grade, sidewalks, platforms, or projections from which they might be accessible to pedestrians for 120V, 120/208V, 120/240V, or 240V circuits.

(2) 12 ft above residential property and driveways, and those commercial areas not subject to truck traffic for 120V, 120/208V, 120/240V, 240V, 277V, 277/480V, or 480V circuits.

(4) 18 ft over public streets, alleys, roads, parking areas subject to truck traffic, driveways on other than residential property, and other areas traversed by vehicles (such as those used for cultivation, grazing, forestry, and orchards).

(5) 24½ ft over track rails of railroads.

Author’s Comment:

Overhead conductors located above pools, outdoor spas, outdoor hot tubs, diving structures, observation stands, towers, or platforms must be installed in accordance with the clearance requirements in 680.8.

Q5. What are the equipotential bonding requirements for permanent pools?

A5. The required equipotential bonding is intended to reduce voltage gradients in the area around a permanently installed pool [680.26(A)].

The parts of a permanently installed pool listed in 680.26(B)(1) through (B)(7) must be bonded together with a solid copper conductor not smaller than 8 AWG with listed pressure connectors, terminal bars, exothermic welding, or other listed means in accordance with 250.8(A) [680.26(B)].

Equipotential bonding isn’t required to extend to or be attached to any panelboard, service equipment, or grounding electrode.

Concrete Pool Shells-Equipotential Bonding [680.26(B)(1)].

Unencapsulated structural reinforcing steel in concrete shells must be bonded together by steel tie wires. [680.26(B)(1)(a)].

Perimeter Surfaces: Equipotential bonding must extend 3 ft horizontally beyond the inside walls of a pool including unpaved, paved, and poured concrete surfaces [680.26(B)(2)].

Author’s Comment:

The NEC doesn’t provide any guidance on the installation requirements for structural reinforcing steel when used as a perimeter equipotential bonding method.

Alternative Means. Where structural reinforcing steel isn’t available (or is encapsulated in a nonconductive compound such as epoxy), equipotential bonding meeting all of the following requirements must be installed [680.26(B)(2)(b)]:

(1) The bonding conductor must be 8 AWG bare solid copper.

(2) The bonding conductor must follow the contour of the perimeter surface.

(3) Listed splicing devices must be used.

(4) The required conductor must be located between 18 in. and 24 in. from the inside walls of the pool.

(5) The bonding conductor must be secured in or under the deck or unpaved surface within 4 in. to 6 in. below the subgrade.

Metallic parts of the pool structure must be bonded to the equipotential grid . [680.26(B)(3)].

Metal forming shells and mounting brackets for no-niche luminaires and speakers must be bonded to the equipotential grid . [680.26(B)(4)].

Metal fittings 4 in. and larger located within or attached to the pool structure, such as ladders and handrails must be bonded to the equipotential grid. [680.26(B)(5)].

Metal parts of electrical equipment associated with the pool water circulating system, such as water heaters, pump motors, and metal parts of pool covers must be bonded to the equipotential grid . [680.26(B)(6)].

Ex: Metal parts of listed double-insulated equipment aren’t required to be bonded.

(a) Double-Insulated Water-Pump Motors. If a double-insulated water-pump motor is installed, a solid 8 AWG copper bonding conductor must be provided for a replacement motor . [680.26(B)(6)(a)].

All fixed metal parts must be bonded to the equipotential grid, including but not limited to, metal-sheathed cables and raceways, metal piping, metal awnings, metal fences, and metal door and window frames. [680.26(B)(7)].

Ex 1: If separated from the pool structure by a permanent barrier that prevents contact by a person.

Ex 2: If located more than 5 ft horizontally from the inside walls of the pool structure.

Ex 3: If located more than 12 ft measured vertically above the maximum water level.

If the pool water doesn’t have an electrical connection to one of the bonded parts described in 680.26(B), an approved corrosion-resistant conductive surface that’s at least 9 sq in. must be in contact with the water. The corrosion-resistance conductive surface must be bonded in accordance with 680.26(B), and be located in an area where it won’t be dislodged or damaged or dislodged during normal pool usage [680.26(C)]

Q6. What are the rules for the installation of boundary seals for both power and limited-energy?

A6. Class I, Division 1, Boundary Seal. A raceway seal fitting must be installed in each raceway that leaves a Class I, Division 1 location within 10 ft of the Class I, Division 1 location on either side of the boundary [501.15(A)(4)].

There must be no fitting, except for a listed explosionproof reducer installed at the raceway seal fitting, between the raceway seal fitting and the point at which the raceway leaves the Class I, Division 1 location.

Ex 1: A raceway boundary seal fitting isn’t required for a raceway that passes completely through the Class I, Division 1 area unbroken with no fittings installed within 1 ft of either side of the boundary.

Ex 2: If the raceway boundary is below grade, the raceway seal can be located above grade, after the raceway emerges from below grade.

Boundary Seal at Unclassified Location. A raceway seal fitting must be installed in each raceway leaving a Class I, Division 2 location. It can be installed on either side of the boundary within 10 ft of the Class I, Division 2 area [501.15(B)(2)].

Except for listed explosionproof reducers installed at the raceway seal fitting, there must be no union, coupling, box, or fitting between the raceway seal fitting 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 permitted under normal operating conditions, and they must be accessible.

Author’s Comment:

• See the definition of “Accessible” as it relates to wiring methods in Article 100.
• The raceway boundary seal at unclassified locations is used 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 completely through the Class I, Division 2 area unbroken with no fittings installed within 1 ft of either side of the boundary.

Ex 2: A raceway boundary seal fitting isn’t required for raceways that terminate in an unclassified location where the metal conduit transitions to cable trays, cablebus, ventilated busways, MI cable, or open wiring if:

(1) The unclassified location is located outdoors or the unclassified location is indoors and the conduit system is entirely in one room.

(2) The raceways must not terminate at an enclosure containing an ignition source in normal operation.

Ex 3: A boundary seal fitting isn’t required for a raceway that passes from an enclosure or a room that’s unclassified, as a result of pressurization, into a Class I, Division 2 location.

Q7. What are the ampacity requirements for flexible cords?

A7. Table 400.5(A)(1) lists the allowable ampacity for copper conductors in flexible cords and flexible cables and Table 400.5(A)(2) lists the allowable ampacity for copper conductors in flexible cords and flexible cables with not more than three current-carrying conductors at an ambient temperature of 86ºF [400.5(A)].

Where the number of current-carrying conductors in a cable or raceway exceeds three, the allowable ampacity of each conductor must be adjusted in accordance with the following multipliers:

If the ambient temperature is other than 86°F, the flexible cord or flexible cable ampacity, as listed in Table 400.5(A)(1) or 400.5(A)(2), must be adjusted by using the ambient temperature correction factors listed in Table 310.15(B)(2)(a).

Author’s Comment:

Temperature ratings for flexible cords and flexible cables aren’t contained in the NEC, but UL listing standards state that flexible cords and flexible cables are rated for 60°C unless marked otherwise.

See 400.13 for overcurrent protection requirements for flexible cords and flexible cables.

Q8. What are the Code rules for installing receptacles in damp or wet locations?

A8. Receptacles installed in a damp location must be installed in an enclosure that’s weatherproof when an attachment plug cap isn’t inserted, and the receptacle cover is closed, or an enclosure that’s weatherproof when an attachment plug is inserted. All nonlocking 15A and 20A, 125V and 250V receptacles in a damp location must be listed as weather resistant [406.9(A)].

Author’s Comment:

Damp locations include locations protected from weather and not subject to saturation with water or other liquids, as well as locations partially protected under canopies, marquees, roofed open porches, and interior locations that are subject to moderate degrees of moisture, such as some basements, barns, and cold-storage warehouses [Article 100].

(B) Wet Locations [406.9(B)].

All 15A and 20A receptacles installed in a wet location must be within an enclosure that’s weatherproof when an attachment plug is inserted [406.9(B)(1)] .

Outlet box hoods must be listed and must be identified for “extra-duty” use. All nonlocking type 15A and 20A, 125V and 250V receptacles in a wet location must be listed as weather resistant.

Author’s Comment:

Exposed plastic surface material of weather-resistant receptacles must have UV resistance to ensure that deterioration from sunlight doesn’t take place, or that it’s minimal. In testing, receptacles are subjected to temperature cycling from very cold to very warm conditions, and then subjected to additional dielectric testing. The rapid transition from the cold to warm temperatures will change the relative humidity and moisture content on the device, and the dielectric test ensures that this won’t create a breakdown of the insulation properties.

Ex: Receptacles rated 15A and 20A that are subjected to routine high-pressure washing spray may have an enclosure that’s weatherproof when the attachment plug is removed.

Author’s Comment:

A wet location is an area subject to saturation with water, as well as unprotected locations that are exposed to weather [Article 100].

Receptacles rated 30A or more installed in a wet location must comply with (a) or (b) [406.9(B)(2)].

(a) Wet Location Covers. A receptacle that’s in a wet location, where the load isn’t attended while in use, must be installed in an enclosure that’s weatherproof when an attachment plug is inserted.

(b) Damp Location Covers. A receptacle installed in a wet location that will only be used while someone is in close proximity to it, such as one used with portable tools, can have an enclosure that’s weatherproof when the attachment plug is removed and the cover is closed.

(C) Bathtub and Shower Space. Receptacles must not be installed within or directly over a bathtub or shower stall.

(E) Flush Mounting with Faceplate. The enclosure for a receptacle installed in an outlet box that’s flush-mounted on a finished surface must be made weatherproof by a weatherproof faceplate that provides a watertight connection between the plate and the finished surface.