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New Sizes for Branch Circuit: Tracing the history of these changes and what’s in the 2023 Code

By Mark C. Ode | Jan 16, 2023
Illustration of an open book reading "NEC" against a backdrop of workers and a crane during sunset. Image by Wikimedia Commons.
For as long as I can remember, the normal branch circuit size in the NEC started at 15A and increased from there.

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For as long as I can remember, the normal branch circuit size in the NEC started at 15A and increased from there. New subsections 210.23(A)(1) and (A)(2), covering multiple outlet branch circuit permissible loads at 10A, have been inserted into the 2023 NEC.

Branch circuit sizes

When stating the normal branch circuit size, recognize that small conductor branch circuit sizes of 7A for 18 AWG in 240.4(D)(1) and 10A for 16 AWG in 240.4(D)(2) were inserted into the 2008 NEC and remain in the 2023 edition. However, looking back into the 2008 NEC Committee Report on Proposals, the proposed reason for the 7A and 10A sizes in the small conductor rule was based on a change that occurred in the 2002 edition of NFPA 79, the Electrical Standard for Industrial Machinery. The proposed text for 240.4(D)(1) and (D)(2) recognized the need for using power circuit conductors, other than for control circuits, at sizes smaller than 14 AWG. The proposal stated that these smaller sizes should be allowed if the condition of use is also provided and use as a branch circuit was severely limited. 

The circuits in 240.4(D) were based on a UL special service investigation conducted for the protection of 18 AWG and 16 AWG copper conductors using class CC, J or T fuses. The panel statement further clarified that the acceptance of these sizes would not, by itself, allow the use of 18 AWG and 16 AWG as conductors for all branch circuit applications.

The small conductor rule in 240.4(D) remains relatively unchanged since the 2008 NEC in that it has definite restrictions. The 18 AWG copper conductors are limited to 7A of overcurrent protection, provided all the following conditions are met: (1) continuous loads not exceeding 5.6A; (2) overcurrent protection provided by one of the following: branch-circuit-rated circuit breakers listed and marked for use with 18 AWG copper conductor; branch-circuit-rated fuses listed and marked for use with 18 AWG copper conductor; or class CC, CF, J or T fuses. In addition, 16 AWG copper conductors are limited to 10A of overcurrent protection provided all the following conditions are met: (1) continuous loads not exceeding 8A; (2) overcurrent protection is provided by one of the following: branch-circuit-rated circuit breakers listed and marked for use with 16 AWG copper conductor; branch-circuit-rated fuses listed and marked for use with 16 AWG copper conductor; or class CC, CF, J or T fuses.

Section 240.10 states supplementary overcurrent protective devices are intended to provide limited overcurrent protection for specific applications and utilization equipment.

 

Term clarifications

Furthermore, the difference between “branch-circuit-rated fuses and circuit breakers” and “supplementary protection” as noted in 240.10 must be understood for what is happening in 240.4(D) and new 210.23(A)(1) and (A)(2). Section 240.10 states supplementary overcurrent protective devices are intended to provide limited overcurrent protection for specific applications and utilization equipment. It further clarifies that supplementary overcurrent protection is used for luminaires, appliances and other equipment, or for internal circuits and equipment components. These devices cannot be used as a substitute for required branch-­circuit overcurrent devices, or in place of the required branch circuit protection.

In addition, 240.10 does not require supplementary overcurrent devices to be readily accessible, while branch circuit devices are required to be. Branch circuit overcurrent protective devices are listed devices designed to be installed in panelboards, switchboards, fusible switches and similar equipment. Short-circuit testing conducted on the listed breakers and fuses is done individually, must open the circuit without damage and the breakers must also function afterward. Component supplementary protectors are generally short-circuit tested with upstream branch circuit protection and don’t need to function at the end of the test.

Back to the example

Let’s get back to the 10A branch circuits in 210.23(A)(1) and (2) in the 2023 NEC and how this will affect branch circuits in dwellings and other installations. Section 210.23 states that in no case can the load exceed the branch-circuit ampere rating. A branch circuit supplying two or more outlets or receptacles must supply only the loads specified according to its size in accordance with 210.23(A) and as summarized in 210.24 Table 210.24(1) for copper and Table 210.24(2). Section 210.23(A)(1) states 10A branch circuit can only supply one or more lighting outlets, dwelling unit exhaust fans on bathroom or laundry room lighting circuits, or a gas fireplace unit supplied by an individual branch circuit. Ten-ampere branch circuits cannot supply receptacle outlets; fixed appliances, except as permitted for individual branch circuits; garage door openers; or laundry equipment. Table 210.24(1) further restricts 10A branch circuits to 14 AWG copper and Table 210.24(2) restricts 10A branch circuits to 12 AWG aluminum and copper-clad aluminum.

Ten-ampere branch circuits are severely limited now as to the loads supplied, but the 2026 NEC will see more changes to these requirements as further testing and additional loads are contemplated.

About The Author

ODE is a retired lead engineering instructor at Underwriters Laboratories and is owner of Southwest Electrical Training and Consulting. Contact him at 919.949.2576 and [email protected]

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