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Both are safe, code-recognized ways to connect a generator to your home when installed correctly. An interlock kit is the cheaper hardware and lets you run any circuit in your panel, but you manage the load yourself, breaker by breaker. A transfer switch powers a fixed set of pre-chosen circuits, often with wattmeters, and is simpler and harder to misuse during an outage.
Which is better depends on your panel, your generator, and how you want outages to go. Below is how each works, a side-by-side comparison, and a simple way to decide. One disclosure up front: we sell transfer switches, so we will be straight about where an interlock is the better choice.
An interlock kit is a metal plate or slide that mounts on your main panel's cover. It physically blocks the main breaker and a dedicated generator breaker from being on at the same time.
During an outage you:
The whole panel is now fed by the generator, and the interlock makes it impossible to have the utility and the generator connected together.
What an interlock needs:
A manual transfer switch mounts next to your panel. The circuits you choose, typically 6 to 12, are rewired to run through it. During an outage you plug in and start the generator, then flip each circuit from Line to Gen. Everything else in the house stays off.
Many switches, such as the Reliance Pro/Tran 2 line, include wattmeters, so you can see how hard the generator is working as you switch circuits on.
| Interlock kit | Manual transfer switch | |
|---|---|---|
| Circuits you can power | Any circuit in the panel | Only the pre-wired circuits (typically 6 to 12) |
| Load management | You turn breakers off and on to stay within the generator's limit | Limited to the chosen circuits; wattmeters on many models |
| Hardware cost | Lower | Higher (about $300 to $650 for common kits) |
| Fit | Must be listed for your specific panel | Works with most panels |
| Panel space | Needs a free breaker slot in the right spot | Mounts beside the panel |
| Ease during an outage | More steps, more room for mistakes | Simple: flip the switches you need |
| Good with large generators | Yes, the whole panel is available | Yes, with a 50A switch, but still limited to chosen circuits |
An interlock kit is usually the better fit when:
A transfer switch is usually the better fit when:
The deciding question: do you want flexibility or simplicity? An interlock gives you the whole panel and asks you to be careful. A transfer switch gives you a short list of circuits and makes it hard to get wrong.
Both are recognized ways to connect a generator safely when they are listed and installed correctly. The thing that is never acceptable is backfeeding a home through a wall outlet with a double-male cord. The CPSC calls that practice extremely dangerous, an electrocution risk to utility workers and neighbors.
Local rules vary. Some inspectors and utilities have specific requirements for interlocks, so check with your local building department before you buy. Either option should be installed with a permit, and we recommend a licensed electrician.
Both involve work inside your main panel. Some jurisdictions allow homeowners to do it with a permit; many require a licensed electrician. An interlock is less wiring than a transfer switch, but it still means installing a breaker and an inlet circuit in a live panel. Hire a licensed electrician unless you are qualified and your local rules allow it.
If the transfer switch side of the comparison fits you, these are in stock at Krato Power as of this writing.
Not sure what size? Our generator transfer switch guide walks through amps and circuit counts, and you can compare every option under manual transfer switches.
Which is better, an interlock or a transfer switch? An interlock is cheaper and lets you use the whole panel, but you manage the load. A transfer switch is simpler and limits you to pre-chosen circuits. Large generators and confident owners tend to favor interlocks; simplicity and overload protection favor a transfer switch.
What is the difference between a manual transfer switch and an interlock? A transfer switch is a separate box that moves selected circuits between utility and generator. An interlock is a plate on your main panel that prevents the main breaker and generator breaker from being on together, so the generator feeds the whole panel.
Are generator interlocks legal? Listed interlock kits installed correctly are accepted in many areas, but local rules vary. Check with your building department and get a permit.
Is an interlock kit cheaper than a transfer switch? The hardware usually is. Installation still requires an inlet box, a generator breaker, and electrical work, so get quotes for both.
Do I still need a power inlet box with an interlock? Yes. The generator connects through an outdoor inlet box wired to the generator breaker.
Want help choosing? Call our team at 888-855-7286 with your panel brand and your generator model, and we will tell you honestly whether a transfer switch or an interlock makes more sense.
This guide is general information, not electrical or professional installation advice. Interlock kits and transfer switches must be listed for your equipment and installed per the manufacturer's instructions and local electrical codes, typically by a licensed electrician with a permit.
Reviewed by the Krato Power team. Questions? Reach us at 888-855-7286.