Terminal Markings in a Panelboard and More

Article 210 Branch Circuits

Article 250 Grounding

Article 300 Wiring Methods

Article 404 Switches

Article 408 Switchboards and Panelboards

Article 430 Motors, Motor Circuits and Controllers

Article 527 Temporary Installations

Also mentioned are the General Information for Electrical Equipment Directory and Volume 1 of the Fire Resistance Directory, both published by Underwriters Laboratories Inc.

Disconnects for motors

Q:What has changed in Article 430 for the disconnecting means for motors? Some electrical inspectors are uncertain about the status of the use of lockable circuit breakers on motor branch circuits.

A:The changes in the 2002 edition require a disconnecting means within sight of the motor, or a permanently installed locking device on the switch or circuit breaker where the motor installation satisfies either parts (a) or (b) of the Exception to 430.102(B). In prior editions of the NEC, the motor disconnect had to be within sight (not more than 50 feet away) of the motor controller, and had to be capable of being locked in the off position if the motor was more than 50 feet away. The 2002 edition requires an additional disconnecting means within sight of the motor unless the installation meets the criteria in the exception to 430.102(B). Part (a) of this Exception does not require a disconnecting means where a disconnect introduces additional or increased hazards. Fine Print Note 1 gives some examples of additional or increased hazards and includes motors over 100 hp, submersible pump motors, variable frequency drives and motors in hazardous locations.

Part (b) of this Exception removes the requirement for a disconnect within sight of the motor in industrial locations with written safety procedures, and qualified people to service the motors and machines.

Where motor installations comply with parts (a) or (b) of the Exception, a permanently installed locking means must be provided on the circuit breaker or disconnect switch. Lock-off devices that do not have provision for accepting a lock do not satisfy the requirement. Lock-off devices that are held in place by the trim cover on a circuit breaker panel are also not acceptable. The lock-off device should be secured to the disconnect switch or circuit breaker.

Use of dimmer switches

Q:Does the Code allow the use of a flush wall-mounted dimmer switch to control a single receptacle that will be used to provide power to a floor lamp in the living room of a residence?

A:The answer is no. General-use dimmer switches should only control permanently installed incandescent luminaires (lighting fixtures). This is the way part (E) of 404.14 reads: “Dimmer Switches. General-use dimmer switches shall be used only to control permanently installed incandescent luminaries (lighting fixtures) unless listed for the control of other loads and installed accordingly.”

Under the category Dimmers, General Use Switch (EOYX) in the General Information for Electrical Equipment Directory (White Book) published by Underwriters Laboratories Inc., the following information appears: “This listing covers dimmers for mounting in flush device boxes or on outlet box covers, unless otherwise stated in the individual listing. They are intended only for the control of permanently installed incandescent fixtures.”

GFCI-protected receptacles

Q:Does the National Electrical Code permit a GFCI-protected receptacle on the outside of a dwelling to be supplied from an Arc-Fault Circuit Interrupter-protected branch circuit that supplies the bedroom? Will such an arrangement cause nuisance tripping of the GFCI or AFCI?

A:Outdoor receptacles installed at dwelling units must be GFCI-protected to comply with 210.8(A)(3). And AFCI protection is required for bedrooms in dwelling units to comply with 210.12(B).

Although both devices are connected to the same branch circuit, there should be no interaction and no nuisance tripping of the GFCI and AFCI because of this arrangement.

Flexible metal conduit in healthcare facilities

Q:Is flexible metal conduit an acceptable wiring method for receptacles and the examining lighting fixture in a patient bedroom in a hospital?

A:Flexible metal conduit may be used as the wiring method in patient care areas under the following limited conditions: The flexible metal conduit is terminated in fittings that are listed for grounding; the circuit conductors in the raceway are protected by overcurrent devices rated 20A or less; the total length of flexible metal conduit, flexible metal tubing, and liquidtight flexible metal conduit does not exceed 6 feet; the conduit is not installed for flexibility. If all of these conditions are satisfied and an insulated copper equipment grounding conductor that meets the size requirements of 250.122 is installed along with the circuit conductors, flexible metal conduit may be used.

Although 250.118(5) recognizes flexible metal conduit as a grounding means without restrictions on length, size of overcurrent protection, etc., the 2003 edition of the Electrical Equipment Directory (White Book) published by Underwriters Laboratories Inc has this sentence under Flexible Metal Conduit (DXVZ): “Flexible Metal conduit longer than six feet has not been judged to be suitable as a grounding means.”

Wiring in air-handling space in a residence

Q: The area above a suspended ceiling in the basement of a one-family dwelling unit is used for return air for the heating/cooling system. Is this space classified as “other space used for environmental air” as mentioned in 300.22 (C) of the NEC? Is nonmetallic sheathed cable a suitable wiring method in this space? If not, what types of wiring methods are permitted?

A: The space above a suspended ceiling that is used for the movement of environmental air as mentioned in 300.22(C) applies to all occupancies: therefore, the space above a drop ceiling in the basement of a residence is covered by 300.22(C). The Exception does not apply to this installation since it only applies to stud or joist spaces that are used for environmental air movement.

Wiring methods that are permitted in this space are mentioned in 300.22(C)(1). Some that are permitted include Type MI cable, Type MC cable without a nonmetallic covering, Type AC cable, factory-assembled multiconductor control or power cable listed for use in environmental air spaces, flexible metal raceways, electrical metallic tubing, intermediate metal conduit and rigid metal conduit. Nonmetallic sheathed cable is not permitted in this space.

Fluorescent fixtures in fire-rated ceilings

Q:Are there any fire-rated fluorescent fixtures suitable for installation in a one-hour fire-rated ceiling?

A:Yes, there are some recessed fluorescent lighting fixtures that are permitted to be installed in a fire-rated ceiling. These luminaires have the following statement in addition to the UL listing mark: “Luminaire Classified for Fire Resistance. Fire Resistance Classification. See Fire Resistance Directory Control No. ___.” Manufacturers that have this classification are found under the title: “Luminaires and Luminaire Assemblies Classified for Fire Resistance (LDHW)” in Volume 1 of the Fire Resistance Directory published by Underwriters Laboratories Inc. It includes classifications that were in effect on Dec. 12, 2002.

Recessed fluorescent fixtures are classified for installation in floor-ceiling designs and wall-partition assemblies. Make sure when selecting a recessed fluorescent fixture for installation in one-hour rated construction that the fixture is classified for that application. Here is an example of the construction details for one manufacturer’s classified fluorescent fixture: “Recessed fluorescent luminaire for use in maximum one-hour fire-rated U300-Series Wall and Partition designs minimum 2-by-4 inch wood studs spaced maximum 16 inches on center and faced on both sides with minimum 5/8-inch thick gypsum board. Luminaires installed in accordance with accompanying instructions. Aggregate area of luminaries not to exceed one per 25 square feet of wall area. Luminaires on opposite sides of a wall or partition shall be separated by a horizontal distance of not less than 16 inches.” Similar detailed specifications apply to ceiling mounted recessed fluorescent fixtures. Generally, fixtures cannot exceed one for every 25 square feet of ceiling area and they cannot be less than 3 feet apart.

Receptacles connected to temporary wiring

Q:Is the assured equipment grounding conductor program a suitable substitute for GFCI-protected receptacles on a construction site?

A:Ground-Fault Protection of 15, 20, and 30A, 125V receptacles supplied from temporary wiring and used by personnel during construction are required to be protected by GFCIs. However, there is an exception for industrial establishments where maintenance and supervision ensure that qualified personnel are involved, and failure of equipment would create a greater hazard or connected equipment is not compatible with GFCI protection. If these conditions exist, an assured equipment grounding conductor program meeting all of the requirements in 527.6(B)(2) is acceptable instead of GFCI protection. Also, the assured equipment grounding conductor program is permitted to be used on all 125V receptacles rated over 30A and all 250V receptacles. Finally, GFCI protected receptacles are not required where cord sets or devices listed for ground fault protection of personnel are provided for portable use.

Terminal markings in a panelboard

Q:May I use the wire terminal markings on lugs in panelboards? For example, the main lugs in a panelboard are marked CU9AL. Do these symbols allow the use of 90 C aluminum conductors at their 90 C ampacity? Also, is it permissible to terminate two neutral conductors in a single hole on the neutral bus?

A:Markings on the main lugs in a panelboard should not be used to select conductor material (copper or aluminum) and conductor insulation temperature ratings. Instructions on the wiring diagram on the inside of the cover generally specify conductor material and temperature rating of the insulation. These instructions must be followed, not the information on the lugs.

You are not allowed to install more than one grounded circuit conductor (may be a neutral) in a single neutral bus terminal. An exception permits parallel grounded conductors under a single terminal where the terminal is identified for more than one wire. This requirement and exception appear in 408.21. 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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