Article 110—Requirements for Electrical Installations; Article 230—Services; Article 250—Grounding and Bonding; Article 517—Health Care Facilities; Article 680—Swimming Pools, Fountains, and Similar Installations; Article 700—Emergency Systems; The 2006 edition of the Guide Information for Electrical Equipment (White Book) published by Underwriters Laboratories Inc. is also mentioned.
Disconnect for baseboard heater
Q: A single-pole thermostat is used to control a 240-volt, single-phase baseboard heater. May this thermostat serve as a disconnecting means for the heater?
The size of the fan motor (if one is present) determines requirements for disconnecting means for fixed electric space heating equipment—whether supplementary overcurrent protection is provided—and the type of occupancy. These requirements are in 424.19 and 424.20. For a heater without a motor, the branch-circuit switch or circuit breaker is a suitable disconnecting means where within sight of the heater or is capable of being locked in the off position.
A switch that is an integral part of a heater and has a marked off position may serve as one of the disconnects, provided that another disconnecting means is located within the dwelling unit or is on the same floor as the heater in multifamily dwellings. For a two-family dwelling unit, the additional disconnecting means may be located either inside or outside of the dwelling units. For a one-family dwelling unit, the service disconnect is permitted to serve as the other disconnecting means. For all other occupancies, the branch-circuit switch or circuit breaker, where readily accessible for servicing the heater, qualifies as the other disconnecting means.
Bonding swimming pools
Q: Is it necessary to provide a bonding grid under a vinyl-lined swimming pool? An equipotential grid seems to be required by 680.26(C).
A: There was a tentative interim amendment (TIA) issued to change the language in 680.26(C) in the 2005 edition of the National Electrical Code (NEC). The Standards Council issued TIA 05-2 on July 29, 2005, with an effective date of Aug. 18, 2005. The TIA revises 680.26(C) and 680.26(C)(1). The third sentence in 680.26 (C) is revised to read: “The equipotential bonding grid shall conform to the contours of the pool and shall extend within or under paved walking surfaces for 1 m (3 ft.) horizontally beyond the inside walls of the pool and shall be permitted to be any of the following: Exception: ‘The equipotential bonding grid shall not be required to be installed under the bottom of or vertically along the walls of vinyl lined polymer wall, fiberglass composite, or other pools constructed of nonconductive materials. Any metal parts of the pool, including structural metal supports, shall be bonded in accordance with 680.26(B). For the purposes of this section, poured concrete, pneumatically applied (sprayed) concrete, and concrete block, with painted or plastered coatings, shall be considered conductive material.’”
This sentence was added to 680.26(C)(1): “Where deck reinforcing steel is not an integral part of the pool, the deck reinforcing steel shall be bonded to other parts of the bonding grid using a minimum 8 AWG solid copper conductor. Connection shall be per 680.26(D).”
If the authority having jurisdiction has adopted this TIA, an equipotential plane on the walls and bottom of the vinyl-lined pool is not required.
Hydromassage bathtub bonding
Q: A hydromassage bathtub is supplied from a receptacle in a metal box. Does the metal outlet box have to be bonded to the hydromassage pump motor with an 8 AWG solid copper wire?
A: If the hydromassage bathtub is permanently installed; equipped with a recirculating piping system, pump and associated equipment; and is filled with water and emptied after each use, Part VII of Article 680 applies.
All receptacles rated 125-volts, single-phase, 30 amperes or less located within 5 feet of the hydromassage bathtub must be ground-fault circuit interrupter (GFCI) protected. Also, all metal piping systems and all grounded metal parts in contact with the water circulating system must be bonded with an 8 AWG copper conductor.
Nursing home emergency system
Q: The electrical drawings for a new nursing home have been submitted for plan review. They show a manual-transfer switch for the equipment system connected to a normal feeder and the loadside of the emergency transfer switch. The generator size is 100 kVA. Would you accept this arrangement?
A: Although this method of connecting the equipment system is not shown in Fine Print Note 517.30, No. 2, it is similar. Therefore, I would accept it. The equipment system for large systems above 150 kVA allows a manual transfer switch for the equipment system. This discussion assumes the nursing home meets the definition of a hospital. If it is not a hospital, wiring and electrical equipment must conform to Chapters 1 through 4, generally, and Chapters 5, 6 and 7 for particular conditions. Article 700 applies to emergency systems that are not covered by Article 517, and 700.6(D) does not allow the emergency system transfer switch to supply other than emergency loads.
Service-entrance conductor busways
Q: Are all UL-listed bus ducts acceptable for use as service-entrance conductors?
A: Bus duct is listed by Underwriters Laboratories Inc. under Busways and Associated Fittings (CWFT). This category includes lighting busway, trolley busway, plug-in busway and short-run busway. Obviously, some of these are not suitable for use as service-entrance conductors. Although 230.43(9) lists busways as an acceptable wiring method for service-entrance conductors, 110.3(B) requires that listed equipment be installed in accordance with its listing. This sentence in the UL “Guide Information for Electrical Equipment (White Book)” appears under the busway category: “Some busways are not intended for use ahead of service equipment and are marked with the maximum rating of overcurrent protection to be used on the supply side of the busway.”
It is also important that a busway used for service-entrance conductors has a short-circuit current rating that is equal to or greater than the available short-circuit current at its line terminals. This information may be found on the busway nameplate.
Q: Are the “test” and “reset” buttons on a receptacle-type GFCI acceptable for switching a bathroom exhaust fan on and off?
A: No. These buttons have not been tested for switching loads. The following paragraph appears in the UL “Guide Information for Electrical Equipment (White Book)” 2006 edition: “The ‘Test’ and ‘Reset’ buttons on the GFCIs are only intended to check for the proper functioning of the GFCI.
“They are not intended to be used as ‘on/off’ controls of motors or other loads, unless the buttons are specifically marked ‘on’ and ‘off.’ Products with ‘on’ and ‘off’ markings have been additionally listed under Motor Controllers, Mechanically-Operated and Solid-State (NMFT).”
Q: A 200-ampere, three-phase, four-wire service to a small commercial building consists of 4 3/0 AWG Type THWN copper conductors. Does the NEC permit the grounding-electrode conductor to run from the metal water pipe to the steel frame of the building then to the grounded-service conductor? The water pipe connection to the steel frame is about 30 feet away, and the grounding-electrode conductor would be connected to the neutral conductor at the service and the building steel at the location of the service.
A: A 4 AWG copper grounding-electrode conductor may be used as indicated. The following paragraph appears in 250.58: “Two or more grounding electrodes that are effectively bonded together shall be considered as a single grounding electrode system in this sense.”
Connections of the grounding-electrode conductor to the grounding electrodes must be made by exothermic welding, listed lugs, listed pressure connectors, listed clamps or other listed means to comply with 250.70.
Q: May a dishwasher in a dwelling unit be cord-and-plug connected to a receptacle under a sink? The cord will pass through the wall of a cabinet to terminate in a duplex receptacle that is also used for the garbage disposer.
FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. He can be reached at 504.734.1720.