Grounding Electrodes, SE Cables and More

Fire pump disconnecting means

Q: Is the disconnect for an electric motor driving a fire pump required to be within sight of the motor or is it permitted to be out of sight if capable of being locked in the off position? Can the disconnect and overcurrent protection be located in a panelboard?

A: Where a disconnect switch or circuit breaker is provided in the fire pump branch circuit, it does not have to be within sight of the fire pump electric motor because there is an isolation switch in the listed fire pump controller.

This switch is usually a molded case switch that is part of the fire pump controller and is connected ahead of the disconnect switch in the fire pump controller.

This isolating switch is required in all fire pump controllers other than limited-service controllers that are permitted for motors rated 30 horsepower or less and are acceptable to the authority having jurisdiction (AHJ).

The requirement for an isolation switch ahead of the disconnecting means in a fire pump controller is in 10.4.2 of NFPA 20-2003 Standard for the Installation of Stationary Pumps for Fire Protection.

Regardless of whether the fire pump controller is for unrestricted service or limited service, the circuit breaker in the controller is a suitable disconnecting means for the fire pump motor because the controller must be within sight of the fire pump motor to comply with 10.2.1 of NFPA 20.

This is what is required: “Controllers shall be located as close as is practical to the motors they control and shall be within sight of the motors.”

If the fire pump motor controller is installed to comply with this rule, the requirement for a motor disconnect within sight of the motor as outlined in 430.102(B) of the National Electrical Code (NEC) is satisfied.

The answer to the second question is no. The disconnecting means for the fire pump branch circuit cannot be located in a panelboard. Acceptable power sources for electric motor-driven fire pumps are included in 695.3 of the NEC.

Where an electric utility is the source, it may be a separate service or a connection ahead of, and not within, the same cabinet, enclosure or vertical switchboard section as the service disconnecting means.

The following are the reasons for separation: “The connection shall be located and arranged so as to minimize the possibility of damage by fire from within the premises and from exposing hazards.”

This same logic applies to other power sources that are acceptable where the electric utility is not considered to be reliable.

Service-entrance conductors are allowed to run directly to the fire pump controller. If this can be accomplished, the installation will be simplified but the fire pump controller must be marked “Suitable for Use as Service Equipment.”

If it is necessary to provide a disconnect and overcurrent protection for the fire pump branch circuit because the service is remote from the fire pump, the following requirements apply: disconnecting means and overcurrent protection must be six times the full-load current of the fire pump motor, the disconnecting means must be marked “Fire Pump Disconnecting Means” with letters at least one inch high, and the disconnecting means must be supervised in the closed position by one of four different methods.

These and other requirements appear in of NFPA-20 and 695.4(B)(1) through (5) in the NEC.

Conductor temperature limitations

Q: Am I permitted to terminate 2/0 AWG copper conductors with Type THHW insulation on a 200-ampere main circuit breaker in a single-family service panelboard that has lugs marked AL9CU? The service is three-wire, 120/240 volt, single-phase.

A: Although this installation is probably acceptable because of the elevated ampacities permitted for 120/240V, three-wire, single-phase, service-entrance conductors that supply dwelling units, lugs that are acceptable for terminating 90°C insulated conductors at their ampacities do not permit the use of the 90°C ampacity shown in Table 310.16 because of limitations on the end-use equipment.

The following information appears in the General Information for Electrical Equipment Directory published by Underwriters Laboratories Inc.: “A 75°C or 90ºC temperature marking on a terminal (e.g. AL7, CU7AL, AL7CU, or AL9, CU9AL, AL9CU) does not in itself indicate that a 75°C or 90°C insulated wire can be used unless the equipment in which the terminals are installed is marked for 75ºC or 90ºC.”

Also, under Panelboards (QEUY), this sentence appears in the commentary: “Unless the panelboard is marked to indicate otherwise, the termination provisions are based on the use of 60ºC ampacities for wire sizes 14-1 AWG, and 75°C ampacities for wire sizes 1/0 AWG and larger.”

Although 90°C insulated conductors are used as service-entrance conductors for the one-family dwelling unit, they may be used for a calculated load of 200 amperes because Table 310.15(B)(6) allows 2/0 AWG copper conductors with 75°C insulation or 90°C insulation to be rated at 200 amperes.

Notice that 75°C 2/0 AWG copper conductors such as Types RHW, THW and THWN are permitted to be rated at 200 amperes; therefore, Type THHW insulation as used in this installation is being used as Type THW insulation with a 75°C rating.

Bonding flexible metal conduit

Q: A properly sized circuit breaker in a service switchboard supplies a 480Y/277V dry-type transformer. The secondary voltage is 208Y/120. I used flexible metal conduit not more than 6 feet long as the wiring method at the transformer for the primary and secondary conductors to reduce hum in the rigid metal conduit that is used as the wiring method for the primary and secondary conductors. The electrical inspector informed me that bonding jumpers are required to bond the flexible metal conduit. I thought that lengths less than 6 feet did not have to be bonded.

A: A change in 250.118 in the 2005 NEC that deals with flexible metal conduit may have caused a misunderstanding. In the 2002 NEC, item (5) of 250.118 reads like this: “(5) Flexible metal conduit where both the conduit and fittings are listed for grounding.”

This phrase gave the impression that some flexible metal conduit was suitable for grounding regardless of length or size.

This phrase was removed from the 2005 edition because listed flexible metal conduit that complies with Item (5) in the 2002 edition does not exist: Only listed flexible metal conduit that meets all of the following conditions is recognized as an equipment-grounding conductor: “a. The conduit is terminated in fittings listed for grounding; b. the circuit conductors contained in the conduit are protected by overcurrent devices rated at 20 amperes or less; c. the combined length of flexible metal conduit and flexible metallic tubing and liquidtight flexible metal conduit in the same ground return path does not exceed 1.8m (6 ft.); d. where used to connect equipment where flexibility is necessary after installation, an equipment grounding conductor shall be installed.”

It is assumed that the overcurrent-protection devices for the primary and secondary conductors exceed 20 amperes; therefore, a properly sized bonding jumper installed inside or outside of the flexible metal conduit is required.

Permission to install the bonding jumper on the outside of the flexible metal conduit is granted by 250.102(E) provided that the length of the equipment-bonding jumper does not exceed 6 feet.

SE cable and a pool panelboard

Q: May I install Type SE cable that has no covering on the ground wire to feed a swimming pool panel in a cabana adjacent to an in-the-ground swimming pool at an apartment complex?

A: Wiring methods for a swimming pool panelboard are permitted to be rigid metal conduit, intermediate metal conduit, liquidtight, flexible nonmetallic conduit or rigid nonmetallic conduit. This information is in 680.25(A).

An exception to this rule allows the use of an approved cable assembly as a feeder between an existing remote panelboard and service equipment where the cable assembly includes an equipment-grounding conductor within its outer sheath.

If the feeder does not qualify under the exception to 680.25(A), the equipment-grounding conductor must be insulated to comply with 680.25(B)(2).

Therefore, the answer is no, Type SE cable with a bare equipment-grounding conductor cannot be used to supply the panelboard that serves swimming pool equipment branch circuits.

Grounding-electrode conductor size

Q: A 4 AWG copper grounding-electrode conductor is required for a 200-ampere service to comply with 250.66 where the grounding electrode is 10 feet or more of buried metal water pipe. What size grounding-electrode conductor is required for two 200-ampere main circuit breaker panelboards that are double-barrel lugged in the meter base?

A: The service-entrance conductors for this service are probably 500 Kcmil copper conductors with 75°C insulation. Where the grounding-electrode conductor is connected to the grounded-service conductor at the service head, the minimum size is 1/0 AWG copper.

If acceptable to the utility company and the authority having jurisdiction, this 1/0 conductor may be connected to the grounded-service conductor terminal in the meter base.

Another method is to run a 4 AWG copper conductor in one continuous length from the neutral bus in one panelboard through a ground clamp connected to the water pipe to the neutral bus in the other panelboard.

These different connection points for the grounding-electrode conductor are permitted by 250.24(A). EC

FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. He can be reached at 504.734.1720. 


About the Author

George W. Flach

Code Q&A Columnist
George W. Flach was a regular contributing Code editor for Electrical Contractor magazine, serving for more than 40 years. His long-running column, Code Q&A, is one of the most widely read in the magazine's history. He is a former chief electrical in...

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