Panel-Matched Interlock Kits: How to Choose the Right One (and Avoid Dangerous Mistakes)
Interlock kits can be a clean whole-panel backup method — but only when the kit is UL-listed and matches your exact panel brand + model. If you can’t confirm that match, don’t guess.
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1) What an interlock kit does
An interlock kit is a mechanical safety device installed on your electrical panel that prevents the main breaker and the generator backfeed breaker from being ON at the same time. That physical “either/or” lockout is what helps prevent dangerous backfeed.
2) When interlocks are a good choice
Interlocks are often a great fit when:
- You want flexibility to choose circuits during an outage.
- You’re comfortable managing loads (turning breakers on/off to avoid overload).
- Your panel can be positively identified (brand + model + breaker family).
- You plan to use a proper inlet + cord + generator breaker + labeling.
| Option | Best for | Tradeoff |
|---|---|---|
| Interlock kit | Whole-panel selection during outage | Must match panel exactly; you manage loads manually |
| Manual transfer switch | Clean “essentials circuits” setup | Limited to selected circuits (6/10-circuit, etc.) |
3) Step-by-step: match your panel the right way
Step A — Identify the panel brand + model
Open the panel door and look for the data label (often on the inside of the door). You’re looking for a model/catalog number and the breaker family.
Step B — Confirm breaker family and position
Interlocks are panel-specific because they’re physically shaped to block a specific breaker position. Confirm the breaker type (family/series) and where the generator breaker will sit.
Step C — Buy only UL-listed / manufacturer-approved matches
Only buy an interlock kit that explicitly lists compatibility with your exact panel model and breaker family. If the listing is vague, that’s a “no.”
4) What to avoid (common mistakes)
- “Universal” interlock kits — interlocks are mechanical and panel-specific by design.
- Drilling/bending/adapting parts to “fit.”
- Wrong breaker type for the panel (interlocks depend on correct breaker family).
- No labeling of generator breaker and operating steps.
- Skipping the inlet/cord sizing (heat + voltage drop + failures).
5) If you can’t confirm the panel model
If you can’t confidently identify your panel brand/model and breaker family, the smart move is a manual transfer switch. It’s clean, code-friendly, and avoids guesswork.
6) FAQ
Are interlock kits “code compliant”?
It depends on the kit, the panel match, and your local AHJ. The safest path is an interlock kit that is clearly listed for your panel model and installed to code with proper labeling and inlet/breaker sizing.
Can I buy a “universal” interlock and make it work?
Don’t. Mechanical fit and listing/compatibility matter. If the listing is vague or requires modification, choose a manual transfer switch instead.
What else do I need with an interlock?
Typically: a generator inlet (often 30A L14-30), a properly sized cord, the correct generator backfeed breaker for your panel family, labeling, and a safe operating procedure.
What’s the simplest safe backup method for most homeowners?
A manual transfer switch for a handful of essentials circuits is often the simplest, cleanest starting point. Interlocks are great when the panel match is confirmed and you want whole-panel flexibility.
Want help choosing the safe path?
If you tell me your panel brand (Square D, Siemens, Eaton, GE, etc.) and what you’re trying to run, I can tell you whether an interlock makes sense or whether a transfer switch is the cleaner move.
Interlock Readiness Check (Safety Gate)
Answer these 4 questions. If you’re unsure on any item, the safe move is a manual transfer switch. This is about preventing dangerous backfeed and avoiding mismatched hardware.