Article 250—Grounding and Bonding; Article 517—Health Care Facilities; Article 680—Swimming Pools, Fountains, and Similar Installations; Article 700—Emergency Systems; Article 702—Optional Standby Systems; Various parts of the 2006 edition of Guide Information for Electrical Equipment (White Book) published by Underwriters Laboratories Inc are also mentioned.
Heating cable pool deck
Q: Does the National Electrical Code (NEC) permit the installation of heating cable in the concrete walkway around an in-ground swimming pool? The branch circuits supplying the heating cable are 20-ampere, 120-volt protected by ground-fault circuit interrupters (GFCIs).
A: Heating cables may be installed in floors of bathrooms and in hydromassage bathtub locations but cannot be installed in the deck around a permanently installed swimming pool.
All electrical equipment installed in decks around pools must comply with Article 680 to satisfy the requirements in 680.4. Therefore, 680.27(C)(3) applies. Part (C)(3), “Radiant Heating Cables Not Permitted,” states, “Radiant heating cables embedded in or below the deck shall not be permitted.” Electric heating installed within 20 feet of the inside walls of the swimming pool may be unit heaters that are 5 feet or more horizontally from the inside walls of the pool or permanently installed radiant heaters that are at least 5 feet horizontally from the inside walls of the pool and mounted at least 12 feet above the pool deck.
Cord-connected electric ranges
Q: Since it is now necessary to provide a four-wire flexible cord and four-wire receptacle for a 120/240 volt, single-phase electric range, why are ranges still being provided with a grounding connection between the grounded branch circuit conductor and the frame of the range? Is this equipment that was manufactured before the Code was changed to require four-wire cords and receptacles?
A: Cord-and-plug connected electrical equipment must be grounded by means of an equipment-grounding conductor run with the power supply conductors in a cable assembly or flexible cord and terminated in a grounding-type attachment plug with one fixed grounding contact. This requirement appears in 250.138(A), and the equipment may also be grounded by a separate wire or strap as covered by part (B) of 250.138. These methods of grounding the frame of an electric range must be used on new installations.
There is an exception to this requirement in 250.140, which excludes existing branch-circuit conductors that do not have an equipment-grounding conductor. These existing branch circuits are allowed to supply replacement electric ranges provided that the four items in the exception are satisfied.
Underwriters Laboratories Inc. decided electric ranges would be shipped with the neutral conductor bonded to the frame of the range. Here is an excerpt, titled “Ranges, Household Electric,” from the 2006 edition of the Guide Information for Electrical Equipment (The White Book): “All electric ranges, wall-mounted and countermounted cooking equipment and combination ranges, intended for nominal 125/250V or less (including those rated 120/208), three-wire, operation are provided with a bonding connection between the frame of the appliance and the neutral to provide grounding in accordance with the provisions of the National Electrical Code. Unless the appliance is marked ‘Warning—Frame Grounded to Neutral of Appliance Through a Link, This Range Not For Use in Mobile Homes Or In Areas Where Local Codes Do Not Permit Grounding Through Neutral.’ Instructions are provided for disconnecting the bond and making a direct connection of the metallic parts of the unit to ground.” This bonding connection must be removed for new installations to comply with the 2005edition of the NEC.
Concrete-encased grounding electrode
Q: The electrical inspectors in our area have been requiring two ground rods for the service to single-
family dwelling units because the water pipe is plastic. With adoption of the 2005 edition of the National Electrical Code, they now require a concrete-encased electrode consisting of one-half inch reinforcing rod at least 20 feet long and one ground rod. Is the ground rod required by any rules in Article 250?
A: No, the ground rod is not required by the NEC where a concrete-
encased grounding electrode is used. Two ground rods are required to supplement the metal water pipe electrode because the metal pipe will probably be replaced with plastic water pipe when a failure occurs in the metal pipe. This same problem does not exist with reinforcing rods in a concrete foundation. The probability of replacing a reinforcing rod in a building foundation does not exist, therefore, it does not have to be supplemented with a ground rod or other made electrode.
It must be remembered that all grounding electrodes that are present at the building must be part of the grounding electrode system as required by 250.50.
Hydromassage bathtub bonding
Q: Is it necessary to bond a metal faucet that is connected to plastic water pipe on a hydromassage tube?
A: The answer is no, although hydromassage bathtubs are required to comply with Article 680—Swimming Pools, Fountains, and Similar Installations as outlined in 680.70, 680.71, 680.72, 680.73 and 680.74 of the NEC. Although 680.74 requires bonding of grounded metal parts with a copper bonding jumper not smaller than an 8 AWG solid conductor, it applies only to “metal water piping systems.” The word “system” exempts the metal water faucet from the bonding requirements.
The word “systems” is also used in 250.104 and requires bonding of metal water piping systems in buildings and structures.
Operating rooms as wet locations
Q: We have a set of plans for remodeling a hospital. The operating rooms have receptacles that are supplied from the isolated power system. We questioned the electrical engineer who prepared the plans about the necessity of supplying operating room receptacles from the isolated power system, and he said the operating rooms were wet locations. Is this a correct interpretation of operating rooms?
A: Yes, it is, if the hospital administrator says they are wet locations. A fine print note in 517.60 under Anesthetizing Location Classification states, “If either of the anesthetizing locations in 517.60(A) or 517.60(B) is designated a wet location, refer to 517.20.” Part (A) covers Hazardous (Classified) Locations, and 517.60(B) covers other-than-hazardous locations.
Receptacles in wet locations must comply with 517.20, which requires protection by ground-fault circuit interrupters where interruption of power can be tolerated or be served by an isolated power system where interruption of power cannot be tolerated. The electrical engineer has specified that the receptacles be supplied by the isolated power system because a power outage caused by a ground-fault is not acceptable in an operating room.
Switches for emergency lighting
Q: Are single-pole wall switches permitted to control exit and emergency lighting?
A: Yes they are, under limited conditions. Switch arrangements and locations are in 700.20, 700.21 and 700.22. Where switches are provided for exit and emergency lighting, they must be located so that only authorized people have control of the emergency lighting, but there are two exceptions. The first allows two or more single-throw switches connected in parallel to control a single circuit where one of these switches is accessible only to authorized people. The second exception allows two or more switches that may energize emergency lights but not disconnect them. It is also pointed out that switches connected in series or three- and four-way switches are not acceptable.
Switches for controlling emergency circuits must be in locations convenient to authorized people to comply with 700.21. In assembly occupancies, theaters, audience areas and similar locations, switches for controlling emergency circuits must be located in the lobby or at a place conveniently accessible thereto. There is also an exception to allow multiple switches where one switch can energize but not de-energize the circuit. Finally, light-actuated switches are permitted to control exterior emergency lights.
Transfer switch for optional standby system
Q: Is a multipole, double-throw enclosed switch suitable for transfer of load from the utility to an on-site generator at a one-family dwelling?
A: A properly sized multipole, double-throw switch is acceptable for this operation. This type of system is referred to in the NEC as an Optional Standby System and is covered by Article 702. The requirements for transfer equipment are in 702.6, and part of this section reads, “Transfer equipment shall be suitable for the intended use and designed and installed so as to prevent the inadvertent interconnection of normal and alternate sources of supply in any operation of the transfer equipment.”
Some double-throw enclosed switches that have been listed by Underwriters Laboratories Inc. for this application are specially marked. The 2006 edition of the Guide Information for Electrical Equipment (White Book) published by UL under the title “Switches, Enclosed (WIAX)” reads, “Double-throw switches that have been investigated for switching a common load from a normal supply to an optional standby system are marked ‘Suitable For Use In Accordance With Article 702 of the National Electrical Code.’” EC
FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. He can be reached at 504.734.1720.