Number of Conductors in an Outlet Box, Connecting Ground Rods and More

By George W. Flach | May 15, 2004
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Article 250 Grounding

Article 314 Outlet, Device, Pull and Junction Boxes; Conduit Bodies, Fittings and Manholes

Article 430 Motors, Motor Circuits and Controllers

Article 440 Air Conditioning and Refrigerating Equipment

Article 517 Healthcare Facilities

Article 695 Fire Pumps

Overcurrent protection for air conditioning equipment

Q:I installed a remote condensing unit (hermetic motor-compressor and condenser fan motor) on a branch circuit that is protected in the panelboard with a standard molded case circuit breaker. Within 10 feet of the air conditioning unit, I have a properly sized and rated fused disconnect switch. Among other things, the nameplate on the unit specifies an HACR-type circuit breaker or fuses as the required overcurrent protection. The electrical inspector has mentioned the use of the circuit breaker that is not marked HACR. Is it necessary to provide an HACR circuit breaker even though a disconnect with fuses is located at the air conditioning unit?

A: No, it is not necessary to change the circuit breaker in the panelboard to one that is marked HACR because properly sized and rated fuses and a disconnect are in the branch circuit.

The location of the disconnecting means is mentioned in 440.14. It must be readily accessible and within sight (not more than 50 feet away) of the equipment.

Since this air conditioning unit is considered as a group motor installation by 430.53, in addition to complying with 440.22, the appropriate rules in 430.53 must also be satisfied.

Part 3 of 430.53(C) requires specially marked circuit breakers for protection of multi-motors supplied from a single branch circuit. This is the way part (3) reads: “Each circuit breaker is one of the inverse time type and listed for group installation.” However, recognized independent testing laboratories have determined that some remote condensing units are adequately protected by standard molded case (inverse time) circuit breakers. Where multimotor equipment has been tested and found to be acceptable when protected by either fuses or circuit breakers, the nameplate will be marked “protect with overcurrent device not exceeding ________ amperes” or similar language.

Number of conductors in an outlet box

Q:A luminaire (lighting fixture) has three lampholders and six fixture wires that are factory spliced to two pigtail conductors. How many conductors are counted for outlet box fill? Does the National Electrical Code permit this luminaire to be installed on a 4-in. box with 7 cubic inches of volume marked in the box? The power wiring to the box is 14/2 with ground NM-B cable.

A:For this calculation I will assume that there are no internal cable clamps or luminaire support fittings such as studs or hickeys. According to 314.16(B)(1), each conductor that originates outside the box is counted, and conductors that do not leave the box are not counted. Therefore, there are six No. 18 fixture wires and three No. 14 wires in the NM cable. According to Table 314.16(B), the six fixture wires have a volume of (6 x 1.5) 9 cubic inches and the No. 14s have a volume of (3 x 2) 6 cubic inches. This results in a minimum volume of (6 + 9) 15 cubic inches, but the Q indicates that a luminaire (lighting fixture) is supplied from the box. And if the luminaire has a dome cover, the exception to 314.16(B)(1) is allowed. Since the exception permits some conductors to be omitted from the calculations, the box might be large enough. Let’s see: A maximum of four fixture wires smaller than No. 14 are not counted, as well as one equipment grounding conductor. This leaves two No. 14s and two No. 18s. Table 314.16(B) requires 2 cubic inches for each No. 14; therefore, (2 * 2) 4 cubic inches are required for the nonmetallic cable conductors. Two No. 18s must also be included in the calculation (2 * 1.5) resulting in a volume of 3 cubic inches. Adding these two figures together (3 + 4) results in 7 cubic inches, which means that the box is big enough for the luminaire provided there are no luminaire (fixture) studs or hickeys in the box, an external cable connector fastens the cable to the box, and the luminaire has a domed or similar canopy.

Wiring pressure maintenance for fire pump system

Q:Do the requirements of 695.3 and 695.4(B)(1) include jockey pumps as the plural term “pump motors” is used in these rules? If not, and realizing that a jurisdiction does not adopt NFPA 20 Standard for the Installation of Stationary Pumps for Fire Protection, what requirements in the National Electrical Code apply to jockey pumps?

A: It is often necessary to have more than one fire pump on a property because of water volume requirements, excessive height of a structure, or for other reasons. A jockey pump is a pressure maintenance pump that is part of the fire protection system.

A definition and an explanation in NFPA 20 should help in understanding the differences in fire pumps and jockey pumps. Fire pump units are defined as “an assembled unit consisting of a fire pump driver, controller, and accessories.”

Meanwhile, NFPA 20 explains that “Pressure maintenance (jockey or make-up pumps) shall have rated capacity, not less than the normal leakage rate. The pumps shall have discharge pressure sufficient to maintain the desired fire protection system pressure.”

Notice under the Scope of 695.1 in the National Electrical Code in (B)(2) that pressure maintenance pumps are not covered in Article 695—Fire Pumps. Although 695.3(A) allows the jockey pump to be supplied by the same circuit as the fire pump, it is not necessary. Since jockey pumps are not covered by Article 695, any of the wiring methods in Chapter 3 that are suitable for the occupancy and environment may be used to wire the pump. Also, Article 430 applies for sizing the motor branch circuit conductors, overcurrent protection and motor controller. The motor controller must be activated by a water pressure switch in the control circuit.

Connecting ground rods

Q:Does the NEC require listed ground rods for use as grounding electrodes? Are 5/8-inch diameter, 8-foot steel rods required to be listed? Is it acceptable to connect two ground rods spaced about 9 feet apart to the neutral bus in a service disconnect switch without running a grounding electrode conductor between them?

A:There is no requirement in the National Electrical Code for listing of 5/8-inch diameter, 8-feet long steel rods. These words appear in 250.52(A)(5)(b): “Electrodes of iron or steel shall be at least 15.87mm (5/8 inch) in diameter. Stainless steel rods less than 16mm (5/8 inch) in diameter nonferrous rods, or their equivalent shall be listed and shall not be less than 13mm (1/2 inch) in diameter.”

The size of the grounding electrode conductor does not have to be larger than 6 AWG copper and individual grounding electrode conductors may be run to each ground rod. Permission for this is found in 250.64(F) which reads in part: “A grounding electrode conductor shall be permitted to be run to any convenient grounding electrode available in the grounding electrode system or to one or more grounding electrode(s) individually.” Although permitted by the Code, each grounding electrode conductor must have an individual terminal for each conductor or have a terminal that is identified for connection of more than one conductor.

Metal clad cable for patient care areas

Q:Are there any metal clad (MC) cable sheathes that are separately identified for grounding in cable assemblies that also contain an equipment grounding conductor? It is my understanding that an MC cable with an equipment grounding conductor is always considered to be a combination grounding path; that is, the metal sheath and grounding conductor in combination provide a single grounding path. Is any Type MC cable acceptable for wiring receptacles in a patient care are of a hospital?

A:Metal Clad (Type MC) cable is produced with interlocking metal tape, or a smooth or corrugated metal sheath. The metal sheath is usually steel, but aluminum and other metals are also used.

The Type MC cable fabricated from metal tape (the interlocked metal strip type) is not recognized as an equipment-grounding conductor and cannot be used to supply receptacles in patient care areas in a healthcare facility.

Smooth tube and corrugated tube Type MC are acceptable for wiring patient care areas where the metal sheath qualifies as an equipment grounding conductor and the cable assembly includes an equipment ground wire.

It is possible that all Type MC cables with a corrugated or smooth tube metal jacket do not qualify as an equipment grounding conductor. This information appears in the General Information for Electrical Equipment Directory (White Book) published by Underwriters Laboratories Inc. under the title Metal-Clad Cable (PJAE): “The sheath of the smooth or corrugated tube MC cable or a combination of the sheath and a supplemental bare or unstriped green insulated conductor is suitable for use as the required equipment grounding conductor. The supplemental grounding conductor may be sectioned. When sectioned, all sections are identical. Each additional green insulated grounding conductor has either a yellow stripe or a surface marking or both to indicate that it is an additional equipment or isolated grounding conductor. Additional grounding conductors, however marked, are not smaller than the required grounding conductor.”

To be sure that the smooth or corrugated tube Type MC cable has two independent ground paths, the equipment ground wire must be identified with a green insulation and a yellow stripe or surface marking or both. EC

FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. He can be reached at 504.734.1720.


About The Author

George W. Flach was a regular contributing Code editor for Electrical Contractor magazine, serving for more than 40 years. His long-running column, Code Q&A, is one of the most widely read in the magazine's history. He is a former chief electrical inspector for New Orleans and held many other prestigious positions in the electrical industry, including IAEI board of directors and executive committee. He passed away in August 2009.





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