Published In June 2000
Article 100-Definitions; Article 110-Requirements for Electrical Installations; Article 230-Services; Article 240-Overcurrent Protection; Article 250-Grounding; Article 305-Temporary Wiring; Article 695-Fire Pumps. NFPA-20 Standard for the Installation of Stationary Pumps for Fire Protection is also mentioned. Power Sources for a Fire Pump Q: Does the 1999 edition of NFPA-20 Standard for the Installation of Stationary Pumps for Fire Protection require at least two sources of electric power to comply with Section 6-2? A: Section 6-2 reads as follows: "Power Source(s): Power shall be supplied to the electric motor-driven fire pump by a reliable source of two or more approved independent sources, all of which shall make compliance with Section 6-4 possible." Section 6-4 sets limits on voltage drop of 15 percent for starting and 5 percent when the motor is operating at 115 percent of its full-load current rating. There is a typo in the text of Section 6-2. The first "of" that appears in the Section should be changed to "or." The sentence should read in part: "Power shall be supplied to the electric motor-driven fire pump by a reliable source or two or more approved independent sources . . . " Only one reliable power source is required except for high-rise buildings where the height of the structure is beyond the pumping capacity of the fire department apparatus. In this situation, an additional power source, or a redundant diesel engine-driven or redundant steam turbine-driven fire pump must be provided. In Appendix A of NFPA-20 there is a description of a reliable power source. It reads like this: "A reliable source possesses the following characteristics: (1) Infrequent power disruptions from environmental or man-made conditions. (2) A separate service connection or connection to the supply side of the service disconnect. (3) Service and feeder conductors either buried under 2 inches (50 mm) of concrete or encased in 2 inches (50 mm) of concrete or brick within a building." This sentence also appears with this appendix item. "The determination of the reliability of a service is left up to the discretion of the authority having jurisdiction." The electrical inspector must enforce the requirements in Article 695 of the National Electrical Code (NEC). However, if the electrical inspection department does not adopt NFPA-20 and another agency (fire chief, state fire marshal, etc.) does adopt and enforce it, the electrical inspector is probably not the authority having jurisdiction for determining the reliability of the power source. In this case, the electrical inspector should not make a unilateral decision on the reliability of the electric service supplying the fire pump. Where the words "approved" and "authority having jurisdiction" are used, decisions should be reached through joint consultation or the electrical inspector should leave all items that require approval to the agency that is responsible for enforcement of NFPA-20. This is especially true of requirements in Article 695 of the NEC that are preceded by an "x". This symbol means that the text has been extracted from another NFPA Standard. A request for an official interpretation of this text should be made to the NFPA-20 Committee. Lighting Fixtures on a Construction Site Q: Is it necessary to provide mechanical protection for single-tube fluorescent lighting fixtures on a construction site? If the answer is yes, does any manufacturer produce a listed fixture that meets the requirements in Section 305-4(f)? A: The requirement applies to all lamps are used for general illumination. Part (f) of Section 305-4 requires that lamps be protected from accidental contact or breakage by a suitable fixture or lampholder with a guard. I called three electrical supply houses in the New Orleans area and asked if they stocked single-tube fluorescent fixtures with a guard to protect the tube from damage. They all said no. I then asked if they were aware of any manufacturer who made such a fixture. Again the answer was no, but one salesman said that he could probably have them made if I ordered enough of them. Here are two ideas that might satisfy the electrical inspector. Slide a clear plastic tube over the fluorescent tube. If the tube is accidentally hit, the fluorescent tube will break but it will be confined within the plastic tube shield. The other idea is to mount the fixtures vertically on the webs of steel columns at a height of about 4 feet above the floor. The flanges on the steel column should protect the fluorescent tube from accidental contact. Transfer Switch Used as Service Equipment Q: We have a job to wire a large one-family residence. The electrical plans show a transfer switch located ahead (on the line side) of the service disconnecting means. The transfer switch is 200 amperes, 120/240 volts, single-phase. The service-entrance conductors are No. 2/0 copper with Type THWN insulation. A 50 kVA, 120/240-volt, single-phase generator will be connected to one side of the transfer switch. Does the NEC permit a transfer switch to be used in this manner? Is there such a thing as a transfer switch that is suitable for this application? A: Listed transfer switches are available. The transfer switch has to be marked "Suitable for Use as Service Equipment." A 200-ampere 120/240-volt, three-wire, single-phase transfer switch normally has an interrupting rating of 10,000 amperes. If the available fault current at the terminals of the transfer switch is greater than 10,000 amperes, the available fault current will have to be stated when ordering the transfer switch to assure compliance with the NEC. The interrupting rating of the transfer switch must be equal to or greater than the maximum current that is available at the line terminals of the transfer switch. This requirement appears in Section 110-9 of the NEC. Removal of Section 230-83 in the 1999 edition of the Code has caused some confusion about the status of transfer switches used as service equipment. This is the way Section 230-83 read in the 1996 NEC: "Transfer equipment, including transfer switches, shall operate such that all ungrounded conductors of one source of supply are disconnected before any ungrounded conductors of the second source are connected." The two exceptions were also deleted. Code Making Panel No. 4 proposed to delete Section 230-83 and the exceptions in their entirety. The substantiation for this proposal was "Transfer Switches Suitable for Service Equipment Use must comply with Section 230-74 which covers transfer switch requirements." All members eligible to vote were in favor of this proposal. Some Code enforcement people were not happy with this change because they used Section 230-83 to require a transfer switch for optional standby systems that were not permanently installed. Sealing Locknuts Q: Is a single sealing locknut suitable for installation in the top of an outdoor disconnect switch? I would like to use a sealing locknut instead of a hub. A: According to the information in the General Information for Electrical Equipment Directory published by Underwriters Laboratories Inc. listed sealing locknuts used with threaded rigid metal conduit and intermediate metal conduit are suitable for wet locations. The sealing lockout may be installed inside or outside of the enclosure. On the opposite side of the enclosure, an ordinary lockout or sealing lockout may be installed. Sizing Main Bonding Jumper Q: What is the minimum-size main bonding jumper for a 208Y/120-volt service that consists of three 750 kcmil Type THWN aluminum conductors per phase? A: Section 250-28(d) contains requirements for sizing the main bonding jumper. This part requires the use of Table 250-66 until the service conductors exceed 1750 kcmils for aluminum conductors. Since there are three conductors per phase, the equivalent cross-sectional area of one phase conductor is (750 x 3) 2250 kcmils. The main bonding jumper cannot be smaller than 12.5 percent of 2250 kcmils or 282 kcmils. According to Table 8 in Chapter 9, the next-larger size aluminum conductor above 282 kcmils is 300 kcmils. Therefore, the main bonding jumper cannot be smaller than 300 kcmils aluminum. If it is desired to use a copper conductor for the main bonding jumper, I would use 500 kcmil copper conductors with Type THWN insulation in the calculations. Although a 500 kcmil copper conductor with 75 degrees Celsius insulation has an ampacity that is 5 amperes below the ampacity of 750 kcmil aluminum, this small difference should not cause any concern. For copper conductors Table 250-66 runs out at 1100 kcmil; therefore, the 12.5 percent rule has to be used. Three 500 kcmil copper conductors per phase results in a total cross-sectional area of 1500 kcmils. Multiplying 1500 by 0.125 results in a bonding jumper with a minimum size of 187.5 kcmils. Table 8 in Chapter 9 indicates that a No. 4/0 copper bonding conductor is adequate for the three conductors per phase-750 kcmil aluminum conductors. Panelboards in Bathrooms Q: Does the NEC prohibit the installation of panelboards in the locker room area of a bathroom in a fitness center? The locker room is part of the bathroom that has toilets, showers, and wash basins. A: In dwelling units, and guest rooms of hotels and motels, overcurrent devices cannot be installed in bathrooms. This rule is in Section 240-24(e). Although the locker room is in the area that includes basins, showers, and toilets and meets Article 100's definition of a bathroom, the restriction on the location of overcurrent devices in bathrooms does not apply to a fitness center. Therefore, panelboards may be located in the locker room provided that they comply with the clearance requirements in Section 110-26 and that they are not in an area where they can be wet from shower spray or the wash basins. FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. He can be reached at (504) 254-2132.