CODE CITATIONS: Article 225-Outside Branch Circuits and Feeders; Article 230-Services; Article 250-Grounding; Article 400-Flexible Cords and Cables; Article 410-Lighting Fixtures, Lampholders, Lamps, and Receptacles; Article 422-Appliances.
Wiring Fluorescent Fixtures
Q: Is it permissible to use flexible cord to supply a fluorescent lighting fixture where the cord is unbroken from the fixture up through a suspended ceiling tile installation plate that is secured to the ceiling tile and about 30 inches of flexible metal conduit? The conduit terminates in a junction box above the lay-in ceiling. The flexible cord is connected to the branch circuit conductors with screw-on wire connectors.
A: This is not a proper application for flexible cord. There are a number of Code Sections that do not permit this type of installation. For example, Parts (2), (5),
and (6) of Section 400-8 do not permit flexible cord to be installed in this manner.
Item (2) reads: "Where run through holes in walls, structural ceilings, suspended ceilings, dropped ceilings, or floors," flexible cord shall not be used. Item (5) prohibits flexible cords where concealed behind building walls, structural ceilings, suspended ceilings, dropped ceilings, or floors. In addition, Item (6) does not allow flexible cord to be installed in a raceway unless permitted by this Code.
Cord-connected fluorescent fixtures are permitted by Section 410-30 (a) where the fixture is located directly below the outlet box, the flexible cord is visible for its entire length outside of the fixture, and the cord is terminated in a grounding-type attachment cap or busway plug. A cap or plug is not required where the fixture assembly includes a strain relief and canopy.
An acceptable method for wiring these fluorescent fixtures is to use 3/8-inch flexible metal conduit from the junction box to the fixture (provided the distance between the two does not exceed six feet) with two No. 18 fixture wires in the conduit.
Suitable Wiring Methods for Household Storage Tank Water Heaters
Q: May a domestic storage tank water heater be connected to the fixed wiring in a residence by a flexible cord and attachment cap? If the answer is yes, may the attachment cap and receptacle serve as a disconnecting means?
A: Water heaters installed in dwelling units generally have a storage tank with a capacity of less than 120 gallons. For storage-type water heaters with a capacity of 120 gallons or less, the branch circuit must have a rating of 125 percent of the nameplate rating of the heater.
In my opinion, cord-and-plug connections are not allowed for this type of water heater. Section 422-16(a) provides guidelines for allowing flexible cords for connecting appliances. This is part of the rule: "Flexible cord shall be permitted (1) for the connection of appliances to facilitate their frequent interchange or to prevent the transmission of noise or vibration or (2) to facilitate the removal or disconnection of appliances that are fastened in place, where the fastening means and mechanical connections are specifically designed to permit ready removal for maintenance or repair..." These guidelines do not apply to a storage-tank water heater.
In the 1999 edition of the Electric Appliance and Utilization Equipment Directory (Orange Book) published by Underwriters Laboratories, Inc., these two sentences appear: "This listing covers storage-tank water heaters rated 12 kW or less and having a tank capacity of more than one gallon and not more than 120 gallons. They are intended for household use in ordinary locations and permanent connection to the supply source in accordance with the National Electrical Code." Notice the words "permanent connection to the supply source."
Since the flexible cord connection does not satisfy the NEC, the disconnecting means cannot be an attachment plug and receptacle. If the thermostat on the water heater has a marked "off" position, another disconnecting means meeting the requirements of Section 422-33 (a), (b), (c), or (d) may be located somewhere on the premises, depending on the type of occupancy.
If there is no switch or thermostat with an "off" position on the water heater, the branch circuit switch or circuit breaker may serve as the disconnecting means where the switch or circuit breaker is within sight of the water heater or is capable of being locked in the open position.
Equipment Grounding Conductors
Q: How many equipment grounding conductors are required for a 100-ampere, three-phase, three-wire feeder that consists of three No. 2 Type THWN copper conductors, and a 60-ampere, three-phase, four-wire feeder that has four No. 6 Type THWN copper conductors installed underground in a single Schedule 80 nonmetallic conduit? The 1-1/2-inch nonmetallic conduit and feeders supply motors, lighting, receptacles, and desktop machines in a detached office building that is part of a manufacturing plant. The feeders originate in one of the manufacturing buildings.
A: One building is supplying another through two underground feeders in a single raceway. Restrictions on the number of feeders or branch circuits permitted to be supplied from another building mean you should first review
Section 225-30 requirements to find out if more than one feeder can be justified.
Two pages of requirements now appear in the 1999 NEC covering circuits from one building or structure to another building or structure. These rules appear in Sections 225-30 through 225-40.
Assuming you can run these two feeders in compliance with Section 225-30, let's look at the grounding requirements in Article 250.
Only one equipment-grounding conductor is required in the PVC conduit that contains the two feeders. According to Section 250-122 (c), where a single equipment-grounding conductor is run in the same raceway, it has to be sized for the largest overcurrent device protecting conductors in the raceway. Table 250-122 is used to size the equipment-grounding conductor, and for a 100-ampere overcurrent device, a No. 8 copper equipment-grounding conductor is required.
The equipment-grounding conductor can be bare, covered, or insulated. A covered or insulated conductor must have an outer finish that is green or green with one or more yellow stripes. This requirement is in Section 250-119.
The interior metal water piping in the building served must be bonded to the equipment grounding conductor, or to the 100-ampere disconnecting means, where the No. 8 copper equipment grounding conductor terminates on the grounding bus in the disconnect. In addition, the equipment-grounding conductor must be used for grounding, or bonding of equipment, structures, or frames required to be grounded or bonded. The grounded circuit conductor that is part of the 60-ampere feeder should not be grounded in the building served. This is what the last sentence in Section 250-32(b)(1) says: "Any installed grounded conductor shall not be connected to the equipment grounding conductor or to the grounding electrode(s)." In other words, the neutral in the four-wire feeder must not be connected to a bus or lug in the 60-ampere disconnect that is bonded to the enclosure. The bus or lug must be insulated from the metal enclosure.
The equipment grounding conductor must also be connected to the buried metal water pipe, structural steel of the building, and any other electrodes that comply with Part C of Article 250. If a No. 8 copper conductor is used for this purpose, it must be installed in a raceway or protected by cable armor. (See part (b) of Section 250-64.)
Grouping of Service Disconnecting Means
Q: Can one service disconnecting means remotely located from four service switches that are located at the service drop be considered "grouped" if a shunt trip control switch that opens the remote disconnecting means is grouped with the four disconnects at the service drop?
Many cities in the South are allowing shunt trip buttons to serve as the required disconnecting means where local ordinances require outdoor service
disconnecting means. Does this comply with the NEC?
A: The answer to the first question is no. Section 230-71 uses the words "switches" and "circuit breakers" to limit the number of disconnects to six at one location. This is the way part of Section 230-71 reads: "The service disconnecting means for each service permitted by Section 230-2, or for each set of service-entrance conductors permitted by Section 230-40, Exception Nos. 1 to 3, shall consist of not more than six switches or six circuit breakers mounted in a single enclosure, in a group of separate enclosures, or in or on a switchboard."
Section 230-72(a) is also worth mentioning: "The two to six disconnects as permitted in Section 230-71 shall be grouped. Each disconnect shall be marked to indicate the load served."
Other sections in Article 230 discuss disconnecting means, disconnects, and circuit breakers. However, the language in these various sections does not infer that shunt trip buttons are a suitable disconnecting means for service disconnects that are not grouped at one location. Also, a shunt trip button at one location does not satisfy the requirement for grouping if four shunt trip buttons are not provided at the location where the single disconnecting means is remote from the other four.
The second question can only be answered by the authority having jurisdiction (AHJ). If a local ordinance requires the service disconnecting means to be outside, the AHJ must decide if an outdoor shunt trip button satisfies the ordinance. In this case, a shunt trip button could be accepted because the NEC does not require an outside service disconnecting means. Where service equipment is installed indoors in accordance with the NEC, a shunt trip control circuit run to the outside of the building may satisfy the local ordinance, but the AHJ should be consulted in advance.
FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. He can be reached at (504) 254-2132.