Legally required standby power sources

What the code requires

Section 701.12 covers the power sources for legally required standby systems. If the normal supply fails, standby power must be available within the time the application requires, and never more than 60 seconds later. The supply can be one or more of the system types listed in 701.12(A) through (I), in addition to the normal service.

The source has to suit the job. Under 701.12(A), it is chosen based on whether the loads need short-time or long-duration service. Under 701.12(B), the equipment must be located or designed, or both, to reduce the chance of complete failure from floods, fires, icing and vandalism. How long the supply must last is covered in 701.12(C).

A generator approved by your inspector is allowed under 701.12(D)(1) if it is sized under 701.4 and can start automatically when normal power is lost. An outdoor generator with a readily accessible disconnect within sight of the building does not need a second disconnect at the building. If its conductors end at a disconnect in or on the building, that disconnect must meet 225.36.

Under 701.12(F), a separate service may be used where your inspector approves it. It needs separate service drops or laterals that are electrically and physically remote from the other service conductors.

On the job

• Expect your inspector to confirm that standby power picks up the loads within 60 seconds of losing normal power.
• The source is sized under 701.4, using the Article 220 Parts I–IV load calculation or another approved method.
• Standby equipment must be located or designed, or both, so that floods, fire, icing and vandalism are less likely to take it out, as 701.12(B) requires.

What changed in 2023

The 2023 NEC reorganized 701.12 along the same lines as 700.12, including supply duration and microgrids; under 701.12(H), designated on-site standby sources may connect to a microgrid if the system isolates the legally required standby system from all other loads when normal power is lost, or meets 701.4(C).

In California

In the 2025 CEC, HCD (the state housing agency) adopted Chapter 7 except Articles 701 and 760, so ask your building department which rules apply to your building.

Related sections

• NEC 701.4
• NEC 700.12: Emergency power sources and the 10-second rule
• NEC 445.18: Generator disconnect and emergency shutdown
• NEC 225.36
• NEC 701.32

Where this comes from

• Mike Holt (EC&M): NEC Requirements for Emergency and Standby Systems, May 16 2025
• NFPA: 2026 NEC (A2025) CMP-13 First Draft public input report, reprinting 2023 text
• Electrical Contractor: Concluding the 2023 Code Review (M. Earley), Sep 11 2023
• California HCD: 01/23 Final Express Terms, Part 3 (2025 CEC adoption)
• Read the official NEC free at NFPA