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.

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 rules for grounding and bonding transformers?

A1. Separately derived systems must be grounded and bonded in accordance with 250.30(A)(1) through (A)(8).

A neutral-to-case connection must not be made on the load side of the system bonding jumper, except as permitted by 250.142(B).

A system bonding jumper must be installed at the same location where the grounding electrode conductor terminates to the neutral terminal of the separately derived system; either at the separately derived system or the system disconnecting means, but not at both locations [250.30(A)(1) and (5)].

Where the system bonding jumper is installed at the source of the separately derived system, the system bonding jumper must connect the neutral conductor of the derived system to the metal enclosure of the derived system [250.30(A)(1)(a)].

Where the system bonding jumper is installed at the first disconnecting means of a separately derived system, the system bonding jumper must connect the neutral conductor of the derived system to the metal disconnecting means enclosure [250.30(A)(1)(b)].

Author’s Comment:

A system bonding jumper is a conductor, screw, or strap that bonds the metal parts of a separately derived system to the system neutral point [Article 100 Bonding Jumper, System], and it’s sized to Table 250.102(C)(1) in accordance with 250.28(D).

 

Danger: During a ground fault, metal parts of electrical equipment, as well as metal piping and structural steel, will become and remain energized providing the potential for electric shock and fire if the system bonding jumper isn’t installed.

 

CAUTION: Dangerous objectionable neutral current will flow on conductive metal parts of electrical equipment as well as metal piping and structural steel, in violation of 250.6(A), if more than one system bonding jumper is installed, or if it’s not located where the grounding electrode conductor terminates to the neutral conductor.

A supply-side bonding jumper (nonflexible metal raceway or wire) must be run from the derived system to the derived system disconnecting means [250.30(A)(2)].

If the supply-side bonding jumper is of the wire type, it must be sized in accordance with Table 250.102(C)(1), based on the area of the largest ungrounded derived system conductor in the raceway or cable [250.30(A)(2)(a)].

Question: What size supply-side bonding jumper is required for flexible metal conduit containing 300 kcmil secondary conductors?

(a) 3 AWG      (b) 2 AWG      (c) 1 AWG      (d) 1/0 AWG

Answer: (b) 2 AWG [Table 250.102(C)(1)]

If the system bonding jumper is installed at the disconnecting means instead of at the source, the following requirements apply [250.30(A)(3)]:

(a) The neutral conductor must be routed with the ungrounded conductors of the derived system to the disconnecting means and be sized not smaller than specified in Table 250.102(C)(1), based on the area of the ungrounded conductor of the derived system.

(b) If the conductors from the derived system are installed in parallel in two or more raceways, the neutral conductor of the derived system in each raceway or cable must be sized not smaller than specified in Table 250.102(C)(1), based on the area of the largest ungrounded conductor of the derived system in the raceway or cable. In no case is the neutral conductor of the derived system permitted to be smaller than 1/0 AWG [310.10(H)].

Author’s Comment:

If the system bonding jumper is installed at the disconnecting means instead of at the source, a supply side bonding jumper must connect the metal parts of the separately derived system to the neutral conductor at the disconnecting means [250.30(A)(2)].

The grounding electrode for a separately derived system must be as near as practicable, and preferably in the same area where the system bonding jumper is installed and be one of the following [250.30(A)(4)]:

(1) Metal water pipe electrode, within 5 ft of the entry to the building [250.52(A)(1)].

(2) Metal building frame electrode [250.52(A)(2)].

Ex 1: If the water pipe or structural metal electrode aren’t available, one of the following electrodes can be used:

• A concrete-encased electrode encased by not less than 2 in. of concrete, located horizontally or vertically, and within that portion of concrete foundation or footing that’s in direct contact with the earth [250.52(A)(3)].
• A ground ring electrode encircling the building, buried not less than 30 in. below grade, consisting of at least 20 ft of bare copper conductor not smaller than 2 AWG [250.52(A)(4) and 250.53(F)].
• A rod electrode having not less than 8 ft of contact with the soil meeting the requirements of 250.52(A)(5) and 250.53(G).
• Other metal underground systems, piping systems, or underground tanks [250.52(A)(8)].

Note 1: Interior metal water piping in the area served by separately derived systems must be bonded to the separately derived system in accordance with 250.104(D).

When sizing the grounding electrode conductor for a single separately derived system, the grounding electrode conductor must be sized in accordance with 250.66, based on the area of the largest ungrounded conductor of the derived system. A grounding electrode conductor must terminate to the neutral at the same point on the separately derived system where the system bonding jumper is connected [250.30(A)(5)].

Author’s Comment:

System grounding helps reduce fires in buildings as well as voltage stress on electrical insulation, thereby ensuring longer insulation life for motors, transformers, and other system components.

To prevent objectionable neutral current from flowing [250.6] onto metal parts, the grounding electrode conductor must originate at the same point on the separately derived system where the system bonding jumper is connected [250.30(A)(1)].

Ex 1: The grounding electrode conductor is permitted to terminate to the equipment grounding terminal at the derived system or first system disconnecting means in accordance with 250.30(A)(1).

Ex 3: Separately derived systems rated 1 kVA or less aren’t required to be grounded (connected to the earth).

Where there are multiple separately derived systems, a grounding electrode conductor tap from each separately derived system to a common grounding electrode conductor is permitted [250.30(A)(6)]. This connection is to be made at the same point on the separately derived system where the system bonding jumper is connected [250.30(A)(1)].

Ex 1: If the system bonding jumper is a wire or busbar, the grounding electrode conductor tap can terminate to either the neutral terminal or the equipment grounding terminal, bar, or bus in accordance with 250.30(A)(1).

Ex 2: Separately derived systems rated 1 kVA or less aren’t required to be grounded (connected to the earth).

The common grounding electrode conductor can be one of the following [250.30(A)(6)(a)]:

(1) A conductor not smaller than 3/0 AWG copper or 250 kcmil aluminum.

(2) The metal frame of the buildings that complies with 250.52(A)(2) or is connected to the grounding electrode system by a conductor not smaller than 3/0 AWG copper or 250 kcmil aluminum.

Grounding electrode conductor taps must be sized in accordance with Table 250.66, based on the area of the largest ungrounded conductor of the given derived system [250.30(A)(6)(b)].

All tap connections to the common grounding electrode conductor must be made at an accessible location by one of the following methods [250.30(A)(6)(c)]:

(1) A connector listed as grounding and bonding equipment.

(2) Listed connections to aluminum or copper busbars not less than ¼ in. in depth x 2 in. in width

(3) Exothermic welding.

Grounding electrode conductor taps must be connected to the common grounding electrode conductor so the common grounding electrode conductor isn’t spliced.

The grounding electrode conductor must comply with the following [250.30(A)(7)]:

• Be of copper where within 18 in. of the earth [250.64(A)].
• Be securely fastened to the surface on which it’s carried [250.64(B)].
• Be adequately protected if exposed to physical damage [250.64(B)].
• Metal enclosures enclosing a grounding electrode conductor must be made electrically continuous from the point of attachment to cabinets or equipment to the grounding electrode [250.64(E)].

To ensure dangerous voltage from a ground fault is removed quickly, structural steel and metal piping in the area served by a separately derived system must be connected to the neutral conductor at the separately derived system in accordance with 250.104(D) [250.30(A)(8)].

Separately derived systems located outside the building must have the grounding electrode connection made at the separately derived system location [250.30(C)].

Q2. What are the Code rules for grounding and bonding service equipment?

A2. Service equipment supplied from a grounded system must have the grounding electrode conductor terminate in accordance with 250.24(A)(1) through (5).

(1) A grounding electrode conductor must connect the service neutral conductor to the grounding electrode at any accessible location, from the load end of the overhead service conductors, service drop, underground service conductors, or service lateral, up to and including the service disconnecting means.

Author’s Comment:

Some inspectors require the service neutral conductor to be grounded (connected to the earth) from the meter socket enclosure, while other inspectors insist that it be grounded (connected to the earth) only from the service disconnect. Grounding at either location complies with this rule.

(4) When the service neutral conductor is connected to the service disconnecting means [250.24(B)] by a wire or busbar [250.28], the grounding electrode conductor is permitted to terminate to either the neutral terminal or the equipment grounding terminal within the service disconnect.

(5) A neutral-to-case connection isn’t permitted on the load side of service equipment, except as permitted by 250.142(B).

Author’s Comment:

If a neutral-to-case connection is made on the load side of service equipment, dangerous objectionable neutral current will flow on conductive metal parts of electrical equipment [250.6(A)]. Objectionable neutral current on metal parts of electrical equipment can cause electric shock and even death from ventricular fibrillation, as well as a fire.

A main bonding jumper [250.28] is required to connect the neutral conductor to the equipment grounding conductor within the service disconnecting means [250.24(B)].

Q3. What are the rules in using the neutral conductor for bonding of metal parts?

A3. For service equipment: The neutral conductor can be used as the circuit equipment grounding conductor on the supply side or within the enclosure of the service disconnect in accordance with 250.24(B) [250.142(A)(1)].

For separately derived systems: The neutral conductor can be used as the circuit equipment grounding conductor at the source of a separately derived system or within the enclosure of the system disconnecting means in accordance with 250.30(A)(1) [250.142(A)(3)].

Danger: Failure to install the system bonding jumper as required by 250.30(A)(1) creates a condition where dangerous touch voltage from a ground fault won’t be removed.

Except as permitted in 250.30(A)(1) for separately derived systems and 250.32(B) Ex, for separate buildings/structures, the neutral conductor isn’t permitted to serve as an equipment grounding conductor on the load side of service equipment [250.142(B)].

Ex 1: In existing installations, the frames of ranges, wall-mounted ovens, counter-mounted cooking units, and clothes dryers can be connected to the neutral conductor in accordance with 250.140 Ex.

Ex 2: The neutral conductor can be connected to meter socket enclosures on the load side of the service disconnecting means if:

(1) Ground-fault protection isn’t provided on service equipment,

(2) Meter socket enclosures are immediately adjacent to the service disconnecting means, and

(3) The neutral conductor is sized in accordance with 250.122, based on the ampere rating of the occupancy’s feeder overcurrent device.

Q4. What are the rules for receptacle replacement?

A4. When replacing receptacles, remember that arc-fault circuit-interrupter type and ground-fault circuit interrupter type receptacles must be installed at a readily accessible location [406.4(D)].

If an equipment grounding conductor exists, grounding-type receptacles must replace nongrounding-type receptacles and the receptacle’s grounding terminal must be connected to the circuit equipment grounding conductor in accordance with 250.130(C) or 406.4(C) [406.4(D)(1)].

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.

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).

When existing receptacles are replaced in locations where GFCI protection is currently required, the replacement receptacles must be GFCI protected [406.4(D)(3)].

Author’s Comment:

See 210.8 for specific GFCI-protection requirements.

Effective January 1, 2014, where a receptacle outlet is supplied by a branch circuit that requires arc-fault circuit-interrupter protection [210.12(A)], a replacement receptacle at this outlet must be one of the following [406.4(D)(4)]:

(1) A listed (receptacle) outlet branch-circuit type arc-fault circuit-interrupter receptacle.

(2) A receptacle protected by a listed (receptacle) outlet branch-circuit type arc-fault circuit-interrupter type receptacle.

(3) A receptacle protected by a listed combination type arc-fault circuit interrupter type circuit breaker.

Listed tamper-resistant receptacles must be provided where replacements are made at receptacle outlets that are required to be tamper resistant in accordance with 406.12 for dwelling units, guest rooms and guest suites, and child care facilities [406.4(D)(5)].

Weather-resistant receptacles must be provided where replacements are made at receptacle outlets that are required to be so protected in accordance with 406.9(A) and (B) [406.4(D)(6)].

Q5. What are the rules in sizing equipment grounding conductors?

A5. Equipment grounding conductors of the wire type must be sized not smaller than shown in Table 250.122, based on the rating of the circuit overcurrent device; however, the circuit equipment grounding conductor isn’t required to be larger than the circuit conductors [250.122(A)].

If ungrounded conductors are increased in size from the minimum ampacity that’d be required for the load, wire type equipment grounding conductors must be proportionately increased in size according to the circular mil area of the ungrounded conductors [250.122(B)].

Author’s Comment:

Ungrounded conductors are sometimes increased in size to accommodate conductor voltage drop, harmonic current heating, short-circuit rating, or simply for future capacity.

Question: If the ungrounded conductors for a 40A circuit (with 75ºC terminals) are increased in size from 8 AWG to 6 AWG due to voltage drop, the circuit equipment grounding conductor must be increased in size from 10 AWG to _____.

(a) 10 AWG      (b) 8 AWG      (c) 6 AWG      (d) 4 AWG

Answer: (b) 8 AWG

The circular mil (Cmil) area of 6 AWG is 59 percent more than 8 AWG (26,240 Cmil/16,510 Cmil) [Chapter 9, Table 8].

According to Table 250.122, the circuit equipment grounding conductor for a 40A overcurrent device will be 10 AWG (10,380 Cmil), but the circuit equipment grounding conductor for this circuit must be increased in size by a multiplier of 1.59.

Conductor Size = 10,380 Cmil x 1.59

Conductor Size = 16,504 Cmil

Conductor Size = 8 AWG, Chapter 9, Table 8

Question: If the ungrounded conductors for a 40A circuit (with 60ºC terminals) are increased in size from 8 AWG to 6 AWG due to having four current-carrying conductors in a raceway, the circuit equipment grounding conductor must be increased in size from 10 AWG to _____.

(a) An increase isn’t required      (b) 8 AWG      (c) 6 AWG      (d) 4 AWG

Answer: (a) An increase isn’t required

The equipment grounding conductor doesn’t need to be increased in size in this example, because the 6 AWG is the smallest size ungrounded conductor allowed by the Code.

8 AWG rated 40A at 60ºC x 0.80 = 32A after adjustment factors is too small for the circuit example. 6 AWG rated 55A at 60ºC, is required (55A x 0.80 = 44A).

When multiple circuits are installed in the same raceway, cable, or cable tray, one equipment grounding conductor sized in accordance with 250.122, based on the rating of the largest circuit overcurrent device is sufficient [250.122(C)].

For motor branch circuits, The equipment grounding conductor of the wire type must be sized in accordance with Table 250.122, based on the rating of the motor circuit branch-circuit short-circuit and ground-fault overcurrent device [250.122(D)], but this conductor isn’t required to be larger than the circuit conductors [250.122(D)(1)].

Question: What size equipment grounding conductor is required for a 2 hp, 230V, single-phase motor?

(a) 14 AWG      (b) 12 AWG      (c) 10 AWG      (d) 8 AWG

Answer: (a) 14 AWG

Step 1: Determine the branch-circuit conductor size [430.22(A) and Table 310.15(B)(16)] 2 hp, 230V Motor FLC = 12A [Table 430.248] 12A x 1.25 = 15A, 14 AWG, rated 15A at 60°C [Table 310.15(B)(16)]

Step 2: Determine the branch-circuit protection [240.6(A), 430.52(C)(1), and Table 430.248] 12A x 2.50 = 30A

Step 3: The circuit equipment grounding conductor must be sized to the 30A overcurrent device—10 AWG [Table 250.122], but it’s not required to be sized larger than the circuit conductors—14 AWG.

If circuit conductors are installed in parallel in separate raceways or cable as permitted by 310.10(H), an equipment grounding conductor must be installed for each parallel conductor set [250.122(F)]. The equipment grounding conductor in each raceway or cable must be sized in accordance with Table 250.122, based on the rating of the circuit overcurrent device, but it’s not required to be larger than the circuit conductors [250.122(A)].

Equipment grounding conductors for feeder taps must be sized in accordance with Table 250.122, based on the ampere rating of the overcurrent device ahead of the feeder, but in no case is it required to be larger than the feeder tap conductors [250.122(G)].

Q6. What are the GFCI protection requirements for receptacles?

A6. Ground-fault circuit interruption for personnel must be provided as required in 210.8(A) through (D). The ground-fault circuit-interrupter device must be installed at a readily accessible location.

Author’s Comment:

According to Article 100, “readily accessible” means capable of being reached quickly without having to climb over or remove obstacles, or resort to portable ladders.

GFCI protection is required for 15A and 20A, 125V receptacles installed in the following locations in dwelling units [210.8(A)]:

Author’s Comment:

See the definitions of “GFCI” and “Dwelling Unit” in Article 100.

GFCI protection is required for 15A and 20A, 125V receptacles in the bathroom area of a dwelling unit [210.8(A)(1)].

Author’s Comment:

See the definition of “Bathroom” in Article 100.

In the continued interests of safety, proposals to allow receptacles for dedicated equipment in the bathroom area to be exempted from the GFCI protection requirements have been rejected.

GFCI protection is required for 15A and 20A, 125V receptacles in garages, and in grade-level portions of accessory buildings used for storage or work areas of a dwelling unit [210.8(A)(2)].

Author’s Comment:

See the definition of “Garage” in Article 100.

A receptacle outlet is required in a dwelling unit attached garage [210.52(G)(1)], but a receptacle outlet isn’t required in an accessory building or a detached garage without power. If a 15A or 20A, 125V receptacle is installed in an accessory building, it must be GFCI protected.

15A and 20A, 125V receptacles located outdoors of dwelling units, including receptacles installed under the eaves of roofs, must be GFCI protected [210.8(A)(3)].

Author’s Comment:

Each dwelling unit of a multifamily dwelling that has an individual entrance at grade level must have at least one GFCI-protected receptacle outlet accessible from grade level located not more than 6½ ft above grade [210.52(E)(2)].

Balconies, decks, and porches that are attached to the dwelling unit and are accessible from inside the dwelling must have at least one GFCI-protected receptacle outlet accessible from the balcony, deck, or porch [210.52(E)(3)].

Ex: GFCI protection isn’t required for a receptacle that’s supplied by a branch circuit dedicated to fixed electric snow-melting or deicing or pipeline and vessel heating equipment, if the receptacle isn’t readily accessible and the equipment or receptacle has ground-fault protection of equipment (GFPE) [426.28 and 427.22].

15A and 20A, 125V receptacles installed in crawl spaces at or below grade of a dwelling unit must be GFCI protected [210.8(A)(4)].

Author’s Comment:

The Code doesn’t require a receptacle to be installed in a crawl space, except when heating, air-conditioning, and refrigeration equipment is installed there [210.63].

GFCI protection is required for 15A and 20A, 125V receptacles located in the unfinished portion of a basement not intended as a habitable room and limited to storage and work areas in dwelling units [210.8(A)(5)].

Ex: A receptacle supplying only a permanently installed fire alarm or burglar alarm system isn’t required to be GFCI protected [760.41(B) and 760.121(B)].

Author’s Comment:

A receptacle outlet is required in each unfinished portion of a dwelling unit basement [210.52(G)(3)].

GFCI protection is required for 15A and 20A, 125V receptacles that serve countertop surfaces in a dwelling unit [210.8(A)(6)].

Author’s Comment:

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 trash compactors, exhaust fans, or kitchen waste disposals.

See 210.52(C) for the location requirements of countertop receptacles.

GFCI protection is required for 15A and 20A, 125V receptacles located within an arc measurement of 6 ft from the outside edge of a sink in dwelling units [210.8(A)(7)].

GFCI protection is required for all 15A and 20A, 125V receptacles located in a dwelling unit boathouse [210.8(A)(8)].

Author’s Comment:

The Code doesn’t require a 15A or 20A, 125V receptacle to be installed in a boathouse, but if one is installed, it must be GFCI protected.

GFCI protection is required for 15A and 20A, 125V receptacles located within 6 ft of the outside edge of a bathtub or shower stall in dwelling units [210.8(A)(9)].

15A and 20A, 125V receptacles installed in laundry areas of a dwelling unit must be GFCI protected [210.8(A)(10)].

For other than dwelling units: GFCI protection is required for 15A and 20A, 125V receptacles installed in the following commercial/industrial locations [210.8(B)]:

15A and 20A, 125V receptacles installed in commercial or industrial bathrooms must be GFCI protected [210.8(B)(1)].

Author’s Comment:

See the definition of “Bathroom” in Article 100.

A 15A or 20A, 125V receptacle isn’t required in a commercial or industrial bathroom, but if one is installed, it must be GFCI protected.

15A and 20A, 125V receptacles installed in a non-dwelling kitchen, even those that don’t supply the countertop surface, must be GFCI protected [210.8(B)(2)].

Author’s Comment:

A kitchen is an area with a sink and permanent provisions for food preparation and cooking [Article 100]

GFCI protection isn’t required for receptacles rated other than 15A and 20A, 125V in these locations.

GFCI protection isn’t required for hard-wired equipment in these locations.

An area such an employee break room with a sink and cord-and-plug-connected cooking appliance such as a microwave oven isn’t considered a kitchen.

15A and 20A, 125V receptacles installed on non-dwelling rooftops must be GFCI protected [210.8(B)(3)].

Author’s Comment:

A 15A or 20A, 125V receptacle outlet must be installed within 25 ft of heating, air-conditioning, and refrigeration equipment [210.63].

Ex 1 to (3): Receptacles on rooftops aren’t required to be readily accessible other than from the rooftop.

15A and 20A, 125V receptacles installed outdoors must be GFCI protected [210.8(B)(4)].

Ex 2 to (3) and (4): GFCI protection isn’t required for a receptacle that’s supplied by a branch circuit dedicated to fixed electric snow-melting or deicing or pipeline and vessel heating equipment, if the receptacle isn’t readily accessible and the equipment or receptacle has ground-fault protection of equipment (GFPE) [426.28 and 427.22].

15A and 20A, 125V receptacles installed within 6 ft of the outside edge of a sink 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.

15A and 20A, 125V receptacles installed indoors in wet locations of non-dwelling units must be GFCI protected [210.8(B)(6)].

15A and 20A, 125V receptacles installed in locker rooms with associated showering facilities must be GFCI protected [210.8(B)(7)].

15A and 20A, 125V receptacles installed in non-dwelling unit garages, service bays, and similar areas must be GFCI protected, unless they’re in show rooms or exhibition halls [210.8(B)(8)].

GFCI protection is required for outlets supplying boat hoists in dwelling unit locations [210.8(C)].

Author’s Comment:

See the definition of “Outlet” in Article 100.

This ensures GFCI protection regardless of whether the boat hoist is cord-and-plug-connected or hard-wired.

Outlets supplying dishwashers in a dwelling unit must be GFCI protected [210.8(D)].