Transfer switches and interlocks for standby power

What the code requires

Section 702.5 requires interconnection or transfer equipment for every optional standby system, such as a home generator. The equipment must suit its use, must be listed, and must be designed and installed so that the standby source and the normal supply cannot be connected to each other by accident.

Some transfer switches install between the utility meter and the meter enclosure. Under 702.5(B), these must be listed meter-mounted transfer switches and must be approved. An informational note points to UL 1008M, the standard for these switches, and another explains that manual and nonautomatic equipment relies on a person to operate it.

Except in dwelling units, 702.5(C) requires the equipment's short-circuit current rating to be field-marked on its exterior, based on the type and settings of the overcurrent device that protects it. If the standby system can run in parallel with the normal source, 702.5(D) also requires it to meet Article 705, Part I or Part II.

On the job

• Transfer equipment must be listed, such as a listed transfer switch or a listed interlock kit. Backfeeding a panel from a generator through an unlisted setup does not meet the code.
• A transfer switch mounted at the meter must be the listed meter-mounted type and must be approved by your inspector.
• Outside of dwelling units, look for the field-marked short-circuit current rating on the outside of the transfer equipment.

Exceptions that matter

• A portable generator may be connected temporarily without transfer equipment only where qualified persons service the installation and the normal supply is isolated by a lockable disconnect or by disconnecting the normal-supply conductors.

What changed in 2023

The 2023 NEC added interconnection equipment to the title, dropped the 2020 limit to systems where the utility is the normal or standby source, moved the existing listing requirement into 702.5(A) rather than adding a new one, and dropped the 2020 rule that meter-mounted transfer switches be the manual type unless rated for automatic loads.

Related sections

• NEC 702.4: Sizing whole-home generators and backup batteries
• NEC 702.7
• NEC 702.12
• NEC 230.82
• NEC 705.12: The 120% rule for solar and battery breakers

Where this comes from

• NFPA: 2026 NEC (A2025) CMP-13 First Draft public input report, reprinting 2023 text
• ExpertCE: How does the 2023 NEC update interconnection and transfer equipment requirements?
• Mike Holt: Summary of the 2023 Changes to the NEC
• Electrical Contractor: Meter-Mounted Transfer Switches (M. Ode), Nov 12 2025
• Read the official NEC free at NFPA