The National Electrical Code (NEC) continues to evolve in response to advances in technology, industry trends, market supply and demand, lessons learned, and public safety. The 2023 Code did not disappoint with new requirements and clarifications. However, clarifications can affect project budget, schedule, and success if they are overlooked.
Selective coordination is one area that can go awry. It was first introduced with the publication of 2005 NEC in Sec. 700.27: “Emergency system(s) overcurrent devices shall be selectively coordinated with all supply side overcurrent protection devices.” Like other new introductions, the Code-Making Panel clarified the intent of the requirement over multiple Code cycles. The 2023 clarification tries to resolve all doubts.
Selective coordination evaluations involve a detailed study of electrical distribution additions, modifications, and replacements by licensed professional engineers or other qualified people who work in the design, installation, or maintenance of electrical systems.
Electrical distribution changes introduce dynamic system changes with the potential for different results. Re-evaluation is required with every change, including any supply-side or load-side alteration. Both the original coordination effort and future reevaluation efforts are simplified by keeping no more than four tiers of overcurrent protection devices (OCPDs) from the main service or emergency power supply to the last branch circuit. Having five or six tiers of cascading OCPDs can make selective coordination difficult or impractical.
Changes to the 2023 NEC
Selective coordination (Sec. 700.32) impacts both non-health care emergency power systems and health care facility life safety electrical distribution systems. New and existing systems are commonly served by an on-site power supply system, including generators, inverters, and other listed/approved alternative stored energy systems.
Section 700.32 was reorganized into three parts, including general, replacements, and modifications. All three parts identify a requirement for OCPDs to be selectively coordinated with all supply-side and load-side OCPDs. The replacement or modification of any OCPD requires a reevaluation of the system for selective coordination. Likewise, additions, replacements, and modifications of the emergency or life safety system require reevaluation to ensure selective coordination.
What types of equipment constitute a change?
- Transformers, load-side or line-side.
- OCPDs, including additions, replacements, and modifications of fuses or circuit breakers.
- New distribution equipment including branch panel boards, distribution panels, switchboards, switchgear, and motor control centers.
- New power sources including generators, solar arrays, fuel cells, or microgrids.
What is the impact on the owner or owner’s representative?
If the facility is less than six years old, they’re likely in a good position. The following is recommended for master planning and the life cycle of a facility:
- Maintain. Maintain the professional engineer’s electronic models of the electrical distribution system evaluations for selective coordination, available fault current, and arc flash. It is easier and more cost-effective for the design professional to update the model with small changes as they occur rather than performing a full facility evaluation with every project.
- Partnership. Develop a stewardship partnership with one engineering professional to maintain a backup copy of your electronic models and update them with every addition, modification, or replacement. The design professional will act as a librarian for your electronic model, maintain it, and share it with you and other design professionals who provide you with service as appropriate.
- Budget. Include a project budget line item for the librarian to update the model when you are working with design professionals other than your librarian partner.
If the facility is more than six years old, the owner might have thought these requirements only applied to new construction or additions — but that’s incorrect. The legacy portions of the building’s electrical distribution system are not exempt. An addition, replacement, or modification could arguably result in a range of unforeseen conditions between a few small changes and a complete modification of the building’s emergency or life safety electrical distribution branch circuits.
What can you do to prevent selective coordination conflicts from crippling the budget or schedule of a future facility addition or renovation project? Follow these proactive planning tips.
- Model. Develop an electronic model of the existing electrical distribution system with the help of a licensed design professional. The design professional will provide an initial evaluation to identify any existing concerns.
- Address. Communicate existing selective coordination concerns with a planned approach.
- Maintain and partner. Keep the electronic models in partnership with a trusted license design professional.
Proactive planning will reduce unknowns, supply preliminary insight, and protect renovations/additions so they stay on budget and schedule.
