Cornerstone • Interlocks

Panel-Matched Generator Interlock Kits: How to Choose the Right One (Without Guessing)

A “panel-matched” interlock kit is designed for a specific panel model and breaker layout. If you don’t match the kit to your panel, you can end up with something that looks installed but doesn’t properly block unsafe power combinations.

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 “panel-matched” actually means

“Panel-matched” means the interlock kit is engineered for:

The panel manufacturer (Square D, Siemens, Eaton, GE, etc.)
The panel series/model (the exact catalog/model on the label)
The main breaker style and how breakers mount
A specific breaker position (interlock geometry must physically block unsafe combinations)

Bottom line: A “universal” kit or “close enough” match is where people get hurt — and where inspectors fail installs.

Why matching matters (safety + inspection + reliability)

Safety: The whole point is preventing backfeed and unsafe switching.
Inspection: Many AHJs require a listed kit and correct breaker placement.
Fit: Wrong kits don’t align to the handle throws and can’t properly block the main/generator breaker.
Repeatable use: A matched setup is predictable when you’re stressed during an outage.

Good news: If you correctly identify the panel and follow the manufacturer kit guidance, interlocks are a safe and widely accepted approach.

Step 1: Identify your panel (safe, no-guess method)

You’re looking for the panel label (often inside the door). It typically lists the manufacturer, model/catalog number, and allowed breaker types.

Look for: Brand, catalog/model, and breaker type listing.
Take a clear photo of the label (this is what an electrician/inspector uses).
If the label is missing or unreadable: treat this as a hire an electrician moment.

Do not rely on: breaker handle shape, “looks similar,” Amazon “fits most panels” language, or advice that ignores the panel label.

Common panel brands and breaker families (quick orientation)

This helps you speak the language — but the panel label and manufacturer documentation are the final authority.

Panel Brand	Common Breaker Families	Don’t confuse these
Square D	QO / Homeline	QO ≠ Homeline
Siemens	QP	Siemens QP ≠ Eaton BR
Eaton / Cutler-Hammer	BR / CH	BR ≠ CH
GE	THQL / THQP	THQL vs THQP depends on panel labeling

Important: “Same amps” does not mean “compatible.” Breaker families must be listed for the panel, and the interlock must match the panel layout.

Panel Match Checker (fast reality check)

This doesn’t replace an inspector or electrician — it helps you avoid the most common wrong turns.

Panel brand

Breaker family (from label)

Panel model/catalog number (optional)

I can clearly read the panel label (brand/model/breaker types). The interlock kit I’m considering is listed for my panel model/series (manufacturer docs). The generator backfeed breaker family is explicitly allowed on the panel label. I’ve checked local permit/inspection requirements (AHJ).

Best: manufacturer-listed kit If unsure: electrician Never “close enough”

Codes, AHJ, and “when to hire an electrician”

Most U.S. areas base generator/interlock work on the National Electrical Code (NEC), but adoption and amendments vary by state and municipality. Your AHJ (local inspector/building department) is the final authority.

Permits & inspections: often required for panel work, inlets, or interlocks.
Listed parts: many AHJs require a listed kit that matches the panel model/series.
NEC topics you’ll see referenced: Optional standby systems (often NEC 702) and generators (often NEC 445).

Stop and hire a licensed electrician if: your label is missing/unclear, your panel is unusual, you can’t confirm kit listing, or you don’t know local permit requirements.

What to do next (the safe path)

If you’re going the interlock route, your next “must-be-right” piece is the backfeed breaker family and the inlet/cable sizing.

Backfeed breaker guide (correct type) → Best Start: manual transfer switch → Generator sizing guide →

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