Stumped by the National Electrical Code (NEC)? June 2010

Stumped by the National Electrical Code (NEC)? June 2010

Your most pressing National Electrical Code (NEC) questions answered. All questions and answers are based on the 2008 NEC

Q. What are the conductor termination requirements for copper wire?

A. The general rules for terminations are found in 110.14.

Conductor terminal and splicing devices must be identified for the conductor material, and they must be properly installed and used. See the definition of "Identified" in Art. 100.

Conductor terminations must comply with the manufacturer's instructions as required by 110.3(B). For example, if the instructions for the device state, "Suitable for 18-12 AWG Stranded," then only stranded conductors can be used with the terminating device. If the instructions state, "Suitable for 18-12 AWG Solid," then only solid conductors are permitted. If the instructions state, "Suitable for 18-12 AWG," then either solid or stranded conductors can be used with the terminating device.

Many terminations and equipment are marked with a tightening torque. Conductors must terminate in devices that have been properly tightened in accordance with the manufacturer's torque specifications included with equipment instructions. Failure to torque terminals can result in excessive heating of terminals or splicing devices (due to a loose connection), which can result in a fire because of a short circuit or ground fault. In addition, this is a violation of 110.3(B), which requires all equipment to be installed in accordance with listing or labeling instructions

Conductor terminals must ensure a good connection without damaging the conductors and must be made by pressure connectors (including set screw type) or splices to flexible leads. See the definition of "Connector, Pressure" in Art. 100. Grounding conductors and bonding jumpers must be connected by listed pressure connectors, terminal bars, exothermic welding, or other listed means [250.8(A)].

Terminals for more than one conductor must be identified for this purpose, either within the equipment instructions or on the terminal itself. Split-bolt connectors are commonly listed for only two conductors, although some are listed for three conductors. However, it's a common industry practice to terminate as many conductors as possible within a split-bolt connector, even though this violates the NEC (Figure). Many devices are listed for more than one conductor per terminal. For example, some circuit breakers rated 30A or less can have two conductors under each lug. Grounding and bonding terminals are also listed for more than one conductor under the terminal. Split-bolt connectors for aluminum-to-aluminum or aluminum-to-copper conductors must be identified as suitable for the application.

Q. What are the requirements when using a cord as a disconnecting means for appliances and motors?

A. The requirements are found in 422.33(A) and (B), and read as follows:

(A) Attachment Plugs and Receptacles. A plug and receptacle can serve as the disconnecting means for a cord- and plug-connected appliance.

(B) Cord-and-Plug-Connected Ranges. The plug and receptacle of a cord- and plug-connected household electric range can serve as the range disconnecting means, if the plug is accessible from the front of the range by the removal of a drawer.

Q. What are the conductor fill requirements for signaling circuits?

A. The number and size of conductors or cables in a raceway are limited in accordance with 300.17. Raceways must be large enough to permit the installation and removal of conductors without damaging conductor insulation [725.3(A)]. When all conductors in a raceway are the same size and insulation, the number of conductors permitted can be found in Annex C for the raceway type.

Q. What are the grounding requirements for a generator mounted on a vehicle?

A.The frame of a vehicle-mounted generator isn’t required to be grounded (connected to the earth) if [250.34(B)]:

(1) The generator frame is bonded to the vehicle frame,

(2) The generator only supplies equipment or receptacles mounted on the vehicle or generator, and

(3) The metal parts of the generator and the receptacle grounding terminal are connected to the generator frame.

Q. Please explain the grounding requirements for a service that consist of up to six switches or six circuit breakers mounted in a group of separate enclosures.

A. A grounding electrode conductor is permitted from each service disconnecting means sized not smaller than specified in Table 250.66, based on the area of the ungrounded conductor for each service disconnecting means. Or, a single grounding electrode conductor is permitted from a common location, sized not smaller than specified in Table 250.66, based on the area of the ungrounded conductor at the location where the connection is made [250.64(D)].

Q. When are hospital-grade receptacles required?

A. Not nearly as often as most people think. Only receptacles for inpatient sleeping beds or procedure table beds used in a critical care area (patient bed location) must be listed as “hospital-grade” [517.18(B)]. Hospital-grade receptacles aren’t required in treatment rooms of clinics, medical and dental offices, or outpatient facilities, because these locations don’t have a “patient bed location” as defined in 517.2.

Q. What are the GFCI requirements for receptacles in a commercial repair garage?

A. GFCI protection is required for all 15A and 20A, 125V receptacles used for service and repair operations, such as electrical automotive diagnostic equipment, electric hand tools, portable lighting devices, etc [511.12]. See the definition of "Ground-Fault Circuit Interrupter" in Art. 100.

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