240.4(B) Overcurrent Devices Rated 800 Amperes or Less.

If an adjustable trip circuit breaker is installed in accordance with 240.4(B)(1-3), it is permitted to be adjusted to a value not exceeding the next higher standard size overcurrent device shown in Table 240.6(A) above the ampacity of the conductors being protected where restricted access is provided in accordance with 240.6(C).
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If an adjustable trip circuit breaker is installed in accordance with 240.4(B)(1-3), it is permitted to be adjusted to a value not exceeding the next higher standard size overcurrent device shown in Table 240.6(A) above the ampacity of the conductors being protected where restricted access is provided in accordance with 240.6(C).

Code Change Summary: New language addresses adjustable trip overcurrent devices rated 800 amps or less.

Section 240.4(B) is used when selecting an overcurrent device rated 800 amps or less to protect conductors. Sometimes the ampacity of a conductor does not align with a standard overcurrent device rating from NEC® Table 240.6(A). When this occurs, it is permitted (unless prohibited elsewhere in the NEC) to select the next standard size overcurrent device higher than the ampacity rating of the conductors being protected.

An example would be installing a type THWN, 6 AWG copper branch circuit conductor between an overcurrent device and the utilization equipment, both having 75°C terminals. According to NEC® Table 310.16, this conductor has an ampacity of 65 amps in the 75°C column, but Table 240.6(A) does not show 65 amps as a standard size overcurrent device.

In this case, Section 240.4(B) would permit rounding up to the next higher standard size shown in the table which would be a 70-amp overcurrent device to protect the conductor rated 65 amps.

In the 2023 NEC® a new sentence was added at the bottom of Section 240.4(B) to include adjustable trip overcurrent devices in the rules for rounding up to the next standard size for overcurrent devices rated 800 amps or less. This code change allows adjustable trip overcurrent devices such as a circuit breaker, to be used in the same manner as non-adjustable trip circuit breakers. 

Before this change, using an adjustable trip circuit breaker could result in the need to require a larger conductor size than if a non-adjustable trip circuit breaker was used in the same circuit.

In the 2023 NEC®, according to the new language in Section 240.4(B), if an adjustable trip overcurrent device is installed in accordance with 240.4(B)(1), (B)(2), and (B)(3), it is permitted to be adjusted to a value not exceeding the next higher standard size overcurrent device shown in Table 240.6(A) above the ampacity of the conductors being protected where restricted access is provided in accordance with 240.6(C).

Below is a preview of the NEC®. See the actual NEC® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2023 NEC® edition of NFPA 70.

2020 Code Language:

240.4(B) Overcurrent Devices Rated 800 Amperes or Less. The next higher standard overcurrent device rating (above the ampacity of the conductors being protected) shall be permitted to be used, provided all of the following conditions are met:

(1) The conductors being protected are not part of a branch circuit supplying more than one receptacle for cord-and-plug-connected portable loads.

(2) The ampacity of the conductors does not correspond with the standard ampere rating of a fuse or a circuit breaker without overload trip adjustments above its rating (but that shall be permitted to have other trip or rating adjustments).

(3) The next higher standard rating selected does not exceed 800 amperes.

2023 Code Language:

240.4(B) Overcurrent Devices Rated 800 Amperes or Less. The next higher standard overcurrent device rating (above the ampacity of the conductors being protected) shall be permitted to be used, provided all of the following conditions are met:

(1) The conductors being protected are not part of a branch circuit supplying more than one receptacle for cord-and-plug-connected portable loads.

(2) The ampacity of the conductors does not correspond with the standard ampere rating of a fuse or a circuit breaker without overload trip adjustments above its rating (but that shall be permitted to have other trip or rating adjustments).

(3) The next higher standard rating selected does not exceed 800 amperes.

If the overcurrent protective device is an adjustable trip device installed in accordance with 240.4(B)(1), (B)(2), and (B)(3), it shall be permitted to be set to a value that does not exceed the next higher standard value above the ampacity of the conductors being protected as shown in Table 240.6(A) where restricted access in accordance with 240.6(C) is provided.

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240.4(B) Overcurrent Devices Rated 800 Amperes or Less.

Below is a Real Question from our Electrical Continuing Education Courses for Electrical License Renewal:

Based on the 2023 NEC, which of the following is true in Section 240.4(B)?

A: Adjustable trip circuit breakers are NOT permitted in the NEC.
B: Adjustable trip circuit breakers are NOT included in the rules for 240.4(B).
C: This section pertains to overcurrent devices rated 1000 amps or more.
D: If setting an adjustable trip circuit breaker to the next standard size higher than the ampacity of the conductor, restricted access in accordance with 240.6(C) must be provided.
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