Interlock Kit vs Transfer Switch: Which One Do You Need?

Home electrical panel with circuit breakers

Both let you safely power your house’s wiring from a portable generator without running a maze of extension cords. Here’s the real difference, and which one fits your situation.

BBy the The Brofessionals editors · Updated July 2026 · 6 min read

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Running extension cords through windows during an outage works, but it’s limited and inconvenient. An interlock kit or a manual transfer switch both let a portable generator safely power circuits through your home’s existing wiring — the difference is in cost, installation complexity, and how many circuits you can run at once.

	Interlock Kit	Manual Transfer Switch
What it does	A mechanical device preventing the main breaker and generator breaker from being on simultaneously	A separate sub-panel that lets you manually select which circuits draw from the generator
Cost (parts)	$50 – $150	$200 – $800 (installed cost typically $1,000–$2,200 with labor)
Installation	Simpler, often a few hours for a licensed electrician	More involved, typically a half-day install
Circuit selection	Powers your whole panel through the main breaker (up to generator capacity)	Powers only the specific circuits wired into the transfer switch
Best for	Budget-conscious buyers who want flexibility to power any circuit as needed	Buyers who want dedicated, always-ready circuits without manual breaker switching

Both require a licensed electrician and a permit in most jurisdictions. Neither is a DIY-safe project for anyone without electrical experience — done wrong, either can cause backfeed into the utility grid, which is dangerous for utility workers and illegal virtually everywhere.

How Each One Actually Works

Interlock Kit

A small mechanical bracket installed on your main panel that physically prevents both the main utility breaker and a dedicated generator breaker from being switched on at the same time. During an outage, you flip off the main breaker, flip on the generator breaker, and you’re powering your whole panel (up to your generator’s capacity) through your home’s existing wiring — no rewiring of individual circuits required.

Manual Transfer Switch

A separate small sub-panel installed near your main panel, pre-wired to a chosen set of circuits (typically 6–10). During an outage, you flip a set of switches on the transfer switch panel to move those specific circuits from utility power to generator power. It’s faster to operate once installed, but only the pre-selected circuits are available.

Check Generator Interlock Kit on Amazon → Check Manual Transfer Switch Generator on Amazon →

Which One Should You Choose

Pros

Interlock kit: lower cost and simpler install, with the flexibility to power any circuit in your panel as long as you stay under your generator's total capacity
Interlock kit: a good fit if your power needs vary outage to outage and you'd rather choose circuits on the fly
Transfer switch: faster and simpler to operate during an actual outage, since your key circuits are already pre-wired
Transfer switch: better if you always want the same specific circuits (fridge, sump pump, a few lights) powered without thinking about it

Cons

Interlock kit requires manually switching individual breakers in your main panel each time, which is more hands-on during an outage
Transfer switch limits you to only the circuits it was wired for, even if your generator has spare capacity
Both require professional installation; DIY installation is a serious safety and legal risk

FAQ

Which one is cheaper overall?The interlock kit is cheaper in parts and typically in labor too, since it’s a simpler installation than a dedicated transfer switch sub-panel.

Can I add more circuits to a transfer switch later?Typically only up to the number of slots the switch has — if you might want to power more circuits later, size the transfer switch generously upfront or consider an interlock kit’s whole-panel flexibility instead.

Is either option safe to install myself?No. Both require working inside your live main electrical panel and correctly preventing backfeed, which should always be done by a licensed electrician and typically requires a permit and inspection.

Does either option work with a standby (automatic) generator?No — both interlock kits and manual transfer switches are for portable generators. Standby generators use an automatic transfer switch, a different (and more expensive) component that switches without any manual action.

The Brofessionals Editors

We research generators, solar, garden gear, and DIY tools, then cross-check every pick against manufacturer specs and real-world discussion. No pay-to-play placements — just gear we would run ourselves. How we test.

Interlock Kit vs Transfer Switch: Which One Do You Need?