Skip to main content

Generator interlock and transfer wrapper

Why you care (60 seconds)​

Backfeeding a service is dangerous and illegal. Generator interlocks and transfer equipment prevent parallel utility and generator sources.

Where people lose time​

  • Using unlisted interlock kits or DIY transfer setups.
  • Forgetting required disconnecting means for the generator.
  • Poor labeling that confuses which source is active.

This is​

The rule in plain language​

Optional standby systems must use approved transfer equipment or interlocks to prevent simultaneous connection to normal power, with proper disconnecting and labeling.

When it applies​

Any optional standby generator feeding premise wiring.

What you must do (checklist)​

  • Use listed transfer equipment or listed interlock kits.
  • Provide required generator disconnecting means.
  • Ensure only one source can energize the system at a time.
  • Label the system, source, and operating steps.

Quick examples​

  • A panel interlock must be listed for that specific panel model.
  • A generator disconnect must be readily accessible when required.

This is not​

Common misreads​

  • Using a double-ended cord or backfeed without transfer equipment.
  • Assuming a breaker alone is a transfer device.

What it doesn't cover​

  • Emergency or legally required standby systems.
  • Generator sizing or fuel system design.

False friends​

  • A "mechanical lockout" that is not listed for the panel is not acceptable.

Exceptions & edge cases​

  • Portable generators may use cord-and-plug connections with listed inlet kits.
  • Some AHJs require service-rated transfer equipment even for optional standby.

Cross-references (NEC map)​

  • Primary: 702.4, 702.6, 445.18
  • Secondary: 110.3(B), 230.82

Exam traps​

  • Confusing optional standby with emergency systems.
  • Missing the listing requirement for interlock kits.

Field notes​

  • Keep a one-line diagram and operating steps at the panel.
  • Label "generator backfeed prohibited" and source switching steps.

AHJ / Local amendments notes (placeholder)​

  • Add local amendments or interpretations here.

Revision notes​

  • Draft wrapper created for generator interlocks and transfer equipment.

Related