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From the archives—March 19, 2025
Good morning, the 2023 NEC added Section 240.11 Selective Coordination, which states, “If one or more feeder overcurrent protective devices are required to be selectively coordinated with a service overcurrent protective device ... all feeder overcurrent protective devices supplied directly by the service overcurrent protective device shall be selectively coordinated with the service overcurrent protective device.” I am assuming the definition of a feeder is all circuit conductors between the service equipment, the source of a separately derived system, or other power supply source and the final branch-circuit overcurrent device. Figure 700.32 (under Section 700.32 Selective Coordination) shows an emergency distribution system. The figure basically says that all the OCPDs in the figure need to selectively coordinate with each other, except that “B” does not need to selectively coordinate with “A.” Then if OCPD “D” is a feeder breaker, does that mean that B actually would have to selectively coordinate with A, according to the new Section 240.11?
The requirement in Section 240.11 is a general requirement for selective coordination that applies when one or more feeders are required to be selectively coordinated with the service OCPD upstream from the feeders.
The reason all of the feeder OCPDs are required to be selectively coordinated with the service OCPD is so the service OCPD is not unintentionally opened in the event of a fault at any of the downstream feeder levels. Keep in mind the requirements in Article 240 are generally applied and may be modified or supplemented by requirements in chapters 5–7. The informational note and related figure to Section 700.32 are informational in nature and not enforceable.
From the archives—Dec. 16, 2023
In the 2023 NEC, the informational note/figure to Section 700.32(C) states that OCPD-B is not required to selectively coordinate with OCPD-A because OCPD-B is not an emergency system OCPD. Doesn’t new Section 240.11 require OCPD-B to be selectively coordinated with the service OCPD-A?
In the informational note/figure to 700.32, OCPD-B would not be required to be selectively coordinated with OCPD-A. OCPD-B does not require selective coordination, as it is not an emergency system requiring selective coordination by Section 700.32. As such, Section 240.11 does not apply. The purpose of selectively coordinating OCPDs is to achieve a higher level of reliability by localizing outages. In the one-line diagram in the figure provided in Section 700.32, if either one or both of OCPD-A or OCPD-B trips, the result in outage would be the same.
For more information about selective coordination, see “Know Your Design Requirements." You can also get more out of this discussion through the CQD Spotlight podcast.
Post sponsored by Eaton Corp.
Section 240.11 is the first NEC inclusion of requirements for selective coordination on the normal side of the power system distribution system. Historically, selectivity has only been required within life safety circuits, such as those found in Articles 700, 701 or 708. Section 240.11 was added to 2023 NEC to avoid a needless transfer to emergency backup when possible. The figure below demonstrates this requirement such that if a fault should occur downstream of OCPDs 2, 3 or 4, that portion of the system would be isolated, avoiding opening of OCPD 1, the service disconnect, hence avoiding a transfer to the emergency backup system. Electrical safety and reliability is improved when needless transfers are avoided. Only rely on these safety features when absolutely necessary.
Learn more about protection, reliability and selective coordination
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