Panelboard Mounting Heights, Fire Pump Electric Service, A/C Overcurrent Protection and More

CODE CITATIONS Article 110—Requirements for Electrical Installations; Article 230—Services; Article 240—Overcurrent Protection; Article 350—Flexible Metal Conduit; Article 410—Lighting Fixtures, Lampholders, Lamps, and Receptacles; Article 430—Motors, Motor Circuits, and Controllers; Article 440—Air Conditioning and Refrigeration Equipment Article 695—Fire Pumps; Article 700—Emergency Systems; NFPA 20-1999—Standard for the Installation of Stationary Pumps for Fire Protection Electric Service for a Fire Pump Q: The June 2000 issue of Electrical Contractor magazine included a request for clarification of the requirements for power sources to an electric motor-driven fire pump. Although I agree with your answer, I was disappointed that you did not mention the conflict between Articles 695 and 700 of the National Electrical Code (NEC). To be specific, Section 695-3(a) recognizes a tap ahead of the service disconnecting means as a suitable power supply for an electric-driven fire pump, but Section 700-12(e), which allowed a tap ahead of the service disconnecting means, was deleted in the 1996 edition of the NEC. This created a conflict with Section 695-3(a)(1), which should also have been deleted. A: There is a good reason for providing a separate service or a connection ahead of the service disconnect for an electric motor that drives a fire pump. These two methods of supplying power to a fire pump are normal, and should not be thought of as an emergency power supply. In fact, the word “emergency” does not appear anywhere in Article 695. Section 6-3.2.1 of NFPA 20 “Standard for the Installation of Stationary Pumps for Fire Protection” contains this sentence: “The power supply to the fire pump shall not be disconnected when the plant power is disconnected.” Where utility power is provided, this statement mandates a separate service or a connection ahead of the service disconnecting means. If a service disconnecting means is provided for the fire pump, it must be remotely located from the electric service that supplies the building or structure to minimize the possibility of fire damage from within the premises and from exposing hazards. This disconnect must also be supervised to prevent inadvertent operation. Locking the disconnecting means in the closed position is one method of providing supervision. The disconnect must also be marked with letters that are at least 1-inch high reading, “FIRE PUMP DISCONNECTING MEANS.” These requirements are intended to prevent a firefighter arriving at a building or structure that is on fire from accidentally turning off the electric motor driving a fire pump when he or she turns off all of the electric service switches supplying the building or structure. A separate service or connection ahead of the service disconnect are required to ensure operation of the fire pump even though the service disconnects to the premises are all turned off. Mounting Height Requirements for a Panelboard Q: I am an electrical inspector. During remodeling of a single-family residence, a nonbearing partition (wall) was removed and replaced with a peninsular kitchen counter. The existing wall contained a panelboard with all of the wiring entering the panelboard from the bottom of the enclosure. The electrical contractor reinstalled the panel in one side of the counter and all of the wires entering the panelboard were shortened. The bottom of the enclosure is about 26 inches above the floor. Does the new location of this panelboard violate the NEC? A: Although it may be argued that the new location of the panelboard does not have the 6 feet of clear dedicated space above the equipment as required by Section 110-26(f)(1), I would not reject the installation because of this rule. There is no minimum height for a panelboard in a one-family dwelling. Section 555-6(a) has a minimum height of 24 inches for distribution equipment in mobile homes. This minimum height may be used as a guide for acceptance of the relocated panelboard. Also, it is my understanding that the Standard for Switchboards, Dead Front Type, published by Underwriters Laboratories, does not specify a minimum height for operating handles on disconnect switches and circuit breakers installed in a switchboard. For these reasons I would not reject this installation. All of this information is furnished to help you decide whether to accept or reject this installation. Non-fused Service Disconnect Switch Q: A non-fused 800-ampere service rated disconnect supplies a wireway that feeds five apartments and a house meter. The service conductors are two sets of 500 kcmil copper conductors with Type THWN insulation. The service conductors for each apartment are No. 1/0 copper with Type THWN insulation. The main overcurrent device for each apartment is a 150-ampere, two-pole circuit breaker. The service conductors for the house meter are No. 2 copper with Type THWN insulation. A 100-ampere circuit breaker is provided for the house meter. All of the service equipment is located in a small meter room that is accessible to all tenants. Since the sum of the ampere ratings of the overcurrent devices exceeds the ampacity of the service conductors, is this arrangement Code compliant? Is a non-fused switch permitted for this application? The service entrance conductors are adequate for the load calculated in accordance with Article 220. A: The non-fused switch ahead of the six service disconnects and overcurrent devices is permitted, provided that the service overcurrent devices are located adjacent to it. Section 230-91 covers the location of the service overcurrent devices as follows: “The service overcurrent device shall be an integral part of the service disconnecting means or shall be located immediately adjacent thereto.” The NEC does not require a single main switch for a service. Therefore, the switch could be removed and the service-entrance conductors could be run directly to the wireway. This would result in six disconnects for the apartment building, which are allowed by Section 230-72. If the total load (using appropriate demand factors mentioned in Article 220) is equal to or less than 182 kVA for a 120/240-volt single-phase service, the two sets of 500 kcmil copper conductors with Type THWN insulation are adequate. In fact, Exception No. 3 to Section 230-90(a) allows the sum of the ampere ratings of the overcurrent devices to exceed the ampacity of the service-entrance conductors. It reads: “Two to six circuit breakers or sets of fuses shall be permitted as the overcurrent device to provide the overload protection. The sum of the ratings of the circuit breakers or fuses shall be permitted to exceed the ampacity of the service conductors, provided the calculated load in accordance with Article 220 does not exceed the ampacity of the service conductors.” Although the non-fused switch is not required by the NEC, the installation as described meets Code requirements. If a local ordinance requires a single main switch on all services, this is an economical way of obtaining compliance. Overcurrent Protection for Air Conditioning Equipment Q: As an inspector, I have been told by a manufacturer’s representative that his air conditioning equipment marked “fuses only” can be ignored because the manufacturer’s listing permits the use of an HACR-type circuit breaker, and the manufacturer is using up all its old labels before buying new ones. How should I verify this statement or should I even consider it? Is there a difference in protecting air conditioning equipment with fuses or HACR-type circuit breakers? A: I would not accept the representative’s statement. If the nameplate on the air conditioning equipment specifies fuses, that is what I would require. You have no way of knowing what modifications (if any) were made to obtain listing with an HACR-type circuit breaker for the branch-circuit, short-circuit, and ground-fault protection. There is a difference in the characteristics of fuses and HACR-type circuit breakers. Generally, an inverse time circuit breaker will let through more energy when clearing a line-to-line or line-to-ground fault than a fuse. A remote condensing unit employing a sealed hermetic motor compressor and a condenser fan is considered to be a group installation by Section 430-53(c). Part of this section requires that the branch-circuit, short-circuit, and ground-fault protection be supplied with the equipment or be specified on the product nameplate. As mentioned earlier, an inverse time or molded case circuit breaker will allow more energy to flow during a short-circuit or ground-fault than a fuse. This additional energy could cause overload relay failures, internal wiring pulled out of terminals, etc. Because of these and other potential problems, I would not accept a manufacturer’s representative’s statement that the unit can be protected by an HCAR-type circuit breaker if this type of overcurrent device is not mentioned on the nameplate. You may also use Section 110-3(b) to support your decision. FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. He can be reached at (504) 254-2132.

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