Article 110 Requirements for Electrical Installations
Article 250 Grounding
Article 408 Switchboards and Panelboards
Article 410 Luminaires (Lighting Fixtures), Lampholders, and Lamps
Article 430 Motors, Motor Circuits, and Controllers
Article 680 Swimming Pools, Fountains, and Similar Installations
Article 695 Fire Pumps
NFPA 20 The Standard for the Installation of Stationary Pumps for Fire Protection is also mentioned.
Power supply for a pressure maintenance (Jockey) pump
Q: Is it permissible to connect a jockey pump for a fire sprinkler system to the service that supplies a fire pump? If the answer is yes, how are the conductors and overcurrent protection devices sized?
A: Yes, you are permitted to connect the pressure maintenance (jockey) pump to the service conductors that supply power to the fire pump. However, the splices for the jockey pump conductors cannot be made in the fire pump controller. A junction box or short section of wireway must be provided for this purpose. The fire pump controller enclosure cannot be used as a junction box to supply other equipment including jockey pumps. This prohibition is mentioned 695.6(F).
The service-entrance conductors must have a minimum ampacity of 125 percent of the jockey pump motor and fire pump motor full-load currents. If a disconnecting means and overcurrent protection are provided, the overcurrent protective devices must have an ampere rating that is at least equal to the sum of the locked-rotor currents of the fire pump motor and jockey pump motor. An example should help in understanding the requirements.
Let’s assume a 100-horsepower, 460-volt, three-phase, fire pump and a 5-horsepower, 460-volt, three-phase jockey pump are to be supplied from a 460-volt, three-phase service that supplies no other loads.
Where the service entrance conductors are run directly to a wireway adjacent to or attached to the fire pump controller enclosure a disconnecting means and overcurrent protection for the jockey pump must be grouped with the fire pump controller. The jockey pump disconnecting means and fire pump controller must be marked, “Suitable for Use as Service Equipment” or “Suitable Only for Use as Service Equipment,” and have adequate interrupting ratings.
Service-entrance conductors must have a minimum ampacity of 125 percent of the full-load current of both motors. Table 430-150 shows a full-load current of 124 amperes for the 100-horsepower motor and 7.6 amperes for the 5-horsepower motor. Adding these two figures and multiplying by 1.25 results in a calculated load current of (131.6 x 1.25) 164.5 amperes. According to Table 310.16, 2/0 AWG copper conductors with 75 degrees C insulation are adequate. This same size wire is also needed for the fire pump motor. The conductors that supply the jockey pump do not have to be larger that 12 AWG copper. If it is necessary to install a service disconnecting means and overcurrent protection for the fire pump service, the minimum ampere rating cannot be less than (725+46) 771 or 800 amperes. Seven hundred twenty-five and 46 are the locked rotor amperes for the two motors. These numbers are taken from Table 6-5.1.1 of NFPA 20-1999, Standard for the Installation of Stationary Pumps for Fire Protection and are the same as the values in Table 430.150 of the NEC.
Short-circuit and ground-fault protection for the jockey pump motor can vary between 15 and 25 amperes, depending on the type of overcurrent device selected.
In my opinion, this is not a very safe method of obtaining power for the jockey pump because a short-circuit or ground-fault on the 12 AWG conductors between the connection point at the 2/0 AWG conductors and the line terminals of the jockey pump disconnecting means will result in catastrophic failure of the 12 AWG wires and could cause a fire in the pump room. For this reason, I think a branch circuit originating from a distribution panel supplied by the normal service to the building is a better way of furnishing electric power to the jockey pump.
Bonding water pipe to a swimming pool
Q: Should a metal hose bib that is approximately four feet from the inside edge of an in-the-ground swimming pool be bonded to the reinforcing steel in the pool walls? The metal water pipe is used as the grounding electrode for the service.
A: The exposed metal hose bib has to be connected to the common bonding grid of the swimming pool with a copper conductor not smaller than 8 AWG. Part 680.26(B)(5) requires bonding of metal piping and other exposed metal that are within five feet horizontally of the inside walls of the pool, and not separated from the pool by a permanent barrier.
Part (c) of 680.26 requires that the connections of the 8 AWG solid-copper conductor be made by exothermic welding, pressure connectors or clamps that are labeled as suitable for the purpose and are stainless steel, brass, copper or copper alloy. With one end of the 8 AWG conductor connected to the metal water piping or hose bib, the other end is permitted to be connected to the pool reinforced steel; the wall of a bolted or welded metal pool; an 8 AWG solid copper bonding jumper or to brass or other corrosion-resistant rigid metal or intermediate metal conduit that is part of the bonding grid.
Grounding separately derived systems
Q: A single-phase dry-type transformer with a 480-volt primary and a 120/240-volt secondary is to be installed in a building with no metal water pipe or effectively grounded structural steel that could be used as a grounding electrode conductor. Does the Code permit running the grounding electrode conductor from the midpoint of the secondary in the metal raceway that contains the primary conductors?
A: Yes, that can be done, but you must comply with 250.30, 250.64(E) and 250.97. Since the metal raceway contains conductors operating at more than 250 volts to ground, the requirements for bonding the raceway must be satisfied. Generally, double locknuts are required, or listed fittings that are identified for bonding must be used. Part (E) of 250.64 requires the metal enclosure for the grounding electrode conductor to be electrically continuous from the transformer enclosure to the grounding electrode and to be securely fastened to the ground clamp. Finally, 250.30(A)(1) specifies the minimum size of the grounding electrode conductor and where it is to be connected into the separately derived system.
Grounding metal luminaire (lighting fixture) poles
Q: We just received an electrical drawing that shows 27 metal poles with lighting fixtures for parking lot lighting for a large discount department store. The voltage is 480/277 and the wiring method is nonmetallic conduit underground. The drawing shows an 8-foot ground rod at each pole with a 6 AWG copper conductor running from the rod to the grounding terminal in the pole. There is no equipment grounding conductor in the PVC conduit. Does this method of grounding each pole satisfy the grounding requirements in the NEC?
A: No, it does not. An equipment grounding conductor must be provided in the raceway along with the branch circuit conductors. Its size is based on the ampere rating of the branch circuit overcurrent device. For 30-, 40- or 50-ampere branch circuits, the minimum size is 10 AWG copper. The equipment grounding conductor must be connected to the grounding lug in the pole. Construction and installation requirements for metal poles used to support luminaires (lighting fixtures) are covered in 410.15(B).
The ground rod and grounding electrode conductor provided at the base of each pole is probably intended to “bleed off” voltages from lightning strikes in the vicinity during thunderstorms.
Supplementary grounding electrodes are recognized in 250.54 and are permitted to be connected to equipment grounding conductors, but are not required to meet bonding or earth resistance requirements in 250.50 and 250.56. The last sentence in 250.4(A)(5) reads like this: “The earth shall not be used as the sole equipment grounding conductor or effective ground-fault current path.” Part of the last sentence in 250.54 also does not recognize the earth as an equipment grounding conductor. This is what it says: “… the earth shall not be used as the sole equipment grounding conductor.” Without an equipment grounding conductor in the nonmetallic conduit, the earth is being used as an equipment grounding conductor. And it is likely that a metal pole will remain energized without opening the branch circuit overcurrent device should a phase-to-ground fault develop because of damaged installation on an ungrounded phase conductor in the pole that allows the bare, damaged conductor to make contact with the interior surface of the pole.
Neutral conductor terminations in a panelboard
Q: Is there any rule in the NEC that does not allow the termination of two neutral conductors in the same hole in a neutral bus? How about a neutral conductor and equipment grounding conductor in the same hole on a neutral bus in a service panelboard, or two equipment grounding conductors in the same hole in an equipment grounding bus in a panelboard?
A: The answers to these questions are based on the NEC and manufacturers’ instructions that are furnished with the panelboard. Two neutral conductors cannot be terminated in a single hole in the neutral bus. New 408.21, entitled “Grounding Conductor Terminations,” reads like this: “Each grounding conductor shall terminate within the panelboard in an individual terminal that is not also used for another conductor.” An exception applies to parallel conductors and permits more than one neutral conductor in a single terminal where the terminal is identified for this application. A neutral conductor and equipment grounding conductor in the same terminal are also prohibited by 408.21.
More than one equipment grounding conductor in a single terminal is acceptable if the panelboard is marked to indicate this fact. The last sentence in 110.14(A) says: “Terminals for more than one conductor and terminals used to connect aluminum shall be so identified.” EC
FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. He can be reached at 504.254.2132.