General Installation Requirements, Part VI

Figure 1

National Electrical Code (NEC) Article 110, “Requirements for Electrical Installations,” applies generally to all electrical installations, like all of the articles located in the first four chapters. Topics mentioned in the scope (110.1) include examination and approval, installation and use, access to and spaces about electrical conductors and equipment, enclosures intended for personnel entry, and tunnel installations.


While the scope mentions a number of topics, Article 110 also covers quite a few others. Some of these other subjects include voltages; conductors; wiring integrity; interrupting rating; selective coordination; mechanical execution of work; mounting and cooling of electrical equipment; arc flash hazard warning markings, which includes the new section for field-applied hazard markings; various requirements pertaining to disconnecting means; and enclosure types.


An important topic not previously mentioned is electrical connections. General requirements pertaining to electrical connections are in 110.14; this section is divided into three subheadings, which include terminals, splices and temperature limitations. When conductors are connected to terminal parts, it is required to thoroughly ensure the connection is good and the conductors are not damaged. The connection of conductors to terminal parts shall be made by means of pressure connectors (including set-screw type), solder lugs or splices to flexible leads [110.14(A)]. This section states connection by means of wire-binding screws or studs and nuts that have upturned lugs or the equivalent shall be permitted for 10 AWG or smaller conductors. Terminating an 8 AWG or larger conductor to a wire-binding screw would be a violation of this section.


For example, a 30-ampere (A), single-phase, 208-volt (V), locking receptacle will be installed. This receptacle will be located a considerable distance from the branch-circuit overcurrent device. To keep the voltage drop within the recommended percentage in 210.19(A) Informational Note No. 4, size 8 AWG conductors will be installed. The overcurrent device supplying power to the receptacle will be a 30A, two-pole circuit breaker. The terminations on the breaker are lugs listed for 10 and 8 AWG conductors. Because the lugs are listed for 8 AWG conductors, it shall be permissible to connect 8 AWG conductors to the 30A circuit breaker. The conductors will connect to the receptacle by means of wire-binding screws. In accordance with 110.14(A), 10 AWG conductors are the largest conductors that can be connected to wire-binding screws. Therefore, it would be a violation to wrap the 8 AWG conductors around the terminal screws on the 30A receptacle (see Figure 1).


Since 8 AWG conductors shall not be terminated under wire-binding screws, a different installation method is required for the receptacle in Figure 1. Although there are several methods to make this installation Code-compliant, one would be to splice 10 AWG jumper wires onto the 8 AWG conductors. In accordance with 110.14(A), 10 AWG conductors can be wrapped around the terminal screws on this receptacle. Since smaller conductors (10 AWG) will be spliced to larger conductors (8 AWG), will this be a violation of 240.4? As stated in 240.4, conductors, other than flexible cords, flexible cables and fixture wires, shall be protected against overcurrent in accordance with their ampacities specified in 310.15, unless otherwise permitted or required in 240.4(A) through (G). Splicing 10 AWG jumper wires to 8 AWG conductors will not be a violation in this installation because the overcurrent device is rated 30A. As long as correction or adjustment factors do not lower the allowable ampacity to 25A or less, the 10 AWG conductors will be protected against overcurrent in accordance with the ampacity specified in 310.15 (see Figure 2).


The last sentence in 110.14(A) contains two provisions. The first provision states that only one conductor is permitted under a terminal unless the terminal is listed for more than one conductor. This provision is consistent with 110.3(B), which states that listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling. Mechanical lugs with one terminal (typically referred to as one barrel) are usually listed for one conductor. If more than one conductor were installed in a mechanical lug listed for a single conductor, it would be a violation of 110.14(A) and 110.3(B). There are mechanical lugs manufactured for terminating more than one conductor, but these have a single termination, or barrel, for each conductor. For example, two-barrel mechanical lugs are listed for terminating two conductors, three-barrel mechanical lugs are listed for terminating three conductors, and so on. (see Figure 3).


A stipulation in Article 408 that pertains to grounded conductor terminations in panelboards is similar to the requirement in 110.14(A). Article 408 covers switchboards, switchgear and panelboards. Unless meeting the exception, each grounded conductor shall terminate within the panelboard in an individual terminal that is not also used for another conductor [408.41]. Some terminal bars in panelboards are listed for more than one conductor per terminal, but be careful. There are restrictions. For example, in the listing for the panelboard in this example, two equipment grounding conductors may be terminated per terminal for conductor sizes 14–12 AWG copper or 12–10 AWG aluminum. The listing of this panelboard states that it is permissible to install two conductors under one terminal, but the conductors must be equipment grounding conductors. Installing two grounded or neutral conductors under one terminal shall not be permitted. Also in this example, the conductor sizes are limited to 14–12 AWG copper or 12–10 AWG aluminum (see Figure 4).


The second provision in 110.14(A) states that terminals used to connect aluminum shall be so identified. Most, if not all, aluminum-alloy mechanical lugs are listed for either copper or aluminum conductors. Copper mechanical lugs are usually listed for copper conductors only. A marking of AL9CU or CU9AL on the lug indicates it is suitable for use with either copper or aluminum conductors. The number 9 indicates the lug has a 90°C conductor temperature rating. A marking of AL7CU or CU7AL on the lug indicates it is listed for copper and aluminum conductors. The number 7 indicates the lug has a 75°C conductor temperature rating (see Figure 5).


Requirements for conductor splices are in 110.14(B). The first sentence states conductors shall be spliced or joined with splicing devices identified for the use or by brazing, welding or soldering with a fusible metal or alloy. Splicing or joining conductors with splicing devices is done more often than splicing conductors by brazing, welding and soldering.


Wire connectors (usually referred to in the field as wire nuts) and push-in wire connectors are the most common examples of conductor-splicing devices that are identified for the use. If conductors are soldered, first mechanically and electrically splice or join the conductors so they are secure without solder, and then solder the conductors. All splices and joints and the free ends of conductors shall be covered with an insulation equivalent to that of the conductors or with an identified insulating device. 


With wire connectors and push-in wire connectors, as long as no bare conductor is exposed, the device itself will serve as an equivalent insulation. The last sentence in 110.14(B) requires wire connectors or splicing means installed on conductors that will be directly buried underground to be listed for such use. Regular wire connectors are not listed for direct burial, but a variety of available products are.


Next month’s column continues the discussion of Article 110.

About the Author

Charles R. Miller

Code Contributor

Charles R. Miller, owner of Lighthouse Educational Services, teaches custom-tailored seminars on the National Electrical Code and NFPA 70E. He is the author of “Illustrated Guide to the National Electrical Code” and “Electrician's Exam Prep Manual.”...

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