Required • Safety

Generator Backfeed Breakers: Choosing the Correct Breaker (Why “Close Enough” Is Dangerous)

Interlock kits only work when the generator backfeed breaker is the correct type for your panel. Same amps does not mean compatibility. If you’re evaluating interlocks, start with the panel-matched interlock guide .

Codes + local rules: Generator connections are governed by national standards and your state/local electrical code. Always follow your local building department / inspector (your Authority Having Jurisdiction). If you’re unsure at any point, hire a licensed electrician.

What a generator backfeed breaker actually does

A generator backfeed breaker allows generator power to flow into your main panel. When paired with a properly panel-matched interlock kit , it prevents the generator and utility power from being connected at the same time.

Critical: If the breaker is the wrong family or doesn’t seat correctly, the interlock may not protect you from backfeed — even if it “looks installed.”

Codes, permits, and local authority requirements (don’t skip this)

Most U.S. areas base generator + interlock work on the National Electrical Code (NEC), but your state or city may add rules. Your local building department / inspector (the AHJ) is the final authority. If you’re not sure how to verify compatibility, review the panel-matched interlock guide before buying parts.

Permits & inspections: Many places require a permit and a final inspection for interlocks, inlets, or panel work.
Approved parts: Some jurisdictions require a listed / approved interlock kit and breaker family per the panel label.
NEC topics you’ll see referenced: Optional standby systems (often NEC 702) and generators (often NEC 445).

Practical rule: If the instructions, panel label, or local rules aren’t crystal clear, the safest move is to stop and hire a licensed electrician.

Why this matters: Incorrect generator connections can backfeed the grid, cause fire/shock hazards, damage equipment, and put line workers at risk.

Breaker family matters more than amp rating

Electrical panels are engineered for specific breaker families. Two breakers can both say “30A” and still be mechanically incompatible. That’s a major reason true panel-matched interlock kits exist.

Mini breaker-family lookup (common examples)

Panel Brand	Common Breaker Families	Notes
Square D	QO / Homeline	QO ≠ Homeline. Not interchangeable.
Siemens	QP	Often confused with Eaton BR — not the same.
Eaton / Cutler-Hammer	BR / CH	BR ≠ CH. Different physical designs.
GE	THQL / THQP	Panel label specifies which is allowed.

Rule: If the panel label doesn’t list the breaker family, stop and verify — or hire an electrician.

Amp rating is necessary — but not sufficient

Typical generator backfeed breakers are 30A or 50A, matched to:

Generator output
Inlet type (L14-30 vs 14-50)
Wire gauge

Important: Oversizing the breaker does not give you more power. It removes protection.

Installation position and interlock geometry

Interlocks are designed for a specific breaker position in the panel. If the breaker is in the wrong slot, the interlock cannot physically block unsafe combinations. Positioning is one of the key “panel-match” details covered in the panel-matched interlock guide .

Breaker position must match the interlock design
Main breaker + generator breaker relationship matters
Inspectors check this

Reality check: If you can’t confidently confirm the correct breaker position for the interlock, hire a licensed electrician.

Common mistakes to avoid

Using a “similar looking” breaker
Mixing breaker brands
Buying a breaker not listed on the panel label
Assuming the electrician will “figure it out”
Buying interlock + breaker separately without checking compatibility

Shortcut: If you want the “no guessing” approach, use the panel-matched interlock guide to confirm panel brand/model + kit compatibility first.

Quick safety check (2 questions)

I can identify my panel brand and breaker family from the panel label. The breaker I plan to use is explicitly listed as compatible.

If either answer is “no,” the safer choice is a manual transfer switch — or review the panel-matched interlock guide and hire a licensed electrician if anything is unclear.

Follow local authority: Even when everything seems correct, your local AHJ may require a specific kit, a permit, and an inspection. When in doubt, follow local rules and use a licensed electrician.

Next steps

Panel-matched interlock guide → Best Start: manual transfer switch →

Reminder: This guide is educational. Code requirements vary by state and municipality. Follow your local AHJ and manufacturer instructions. If you’re unsure, hire a licensed electrician.