Transfer Switch Selector: Interlock Kit, Manual or Automatic
Answer four questions to see which safe way of connecting backup power to your home usually fits.
Backup power must be connected to your home wiring safely, never through a wall outlet. Answer four questions about your power source, what you want to run, whether switching must be automatic and your budget, and the selector explains which connection method usually fits. Every option must be installed by a licensed electrician.
How to use this tool
- Choose your backup power source.
- Choose how much of the house you want to power.
- Say whether power must come back without anyone at home.
- Choose a budget level, then read the recommendation and the reasons.
Worked example
With the default answers (portable generator, a few essential circuits, manual switching is fine, lowest cost), the selector recommends a generator interlock kit or a small manual transfer switch, the most affordable code-compliant options for a portable generator. Change the automatic answer to yes and it recommends an automatic transfer switch, which standby generators and whole-home batteries use.
Understanding your results
An interlock kit lets you run any circuit within the generator’s capacity, but you manage the breakers. A manual transfer switch powers a pre-selected set of circuits through a dedicated sub-panel. An automatic transfer switch detects the outage and switches on its own. All three prevent backfeeding the grid when installed correctly.
Common mistakes to avoid
- Using a double-male cord to backfeed through an outlet. It is dangerous and illegal in most places.
- Buying an interlock kit that is not listed for your specific panel.
- Undersizing the inlet and cord for the generator’s output.
- Skipping the permit and inspection, which can affect insurance.
Next steps
Size the generator with the Home Generator Size Calculator.
Frequently asked questions
Interlock kits that are listed for your panel and installed by a licensed electrician are accepted in many jurisdictions, but rules vary. Your electrician and local building department can confirm what is allowed and whether a permit is required. Costs vary widely with the type, the number of circuits and the installation. Manual switches and interlock kits are generally the least expensive; automatic transfer switches for standby generators cost more. Get itemized quotes. We recommend a licensed electrician. Work inside the main panel carries shock and fire risk, and most areas require a permit and inspection.Is a generator interlock kit legal?
What does a transfer switch cost?
Can I install a transfer switch myself?
This tool is for planning and education only. It does not store your entries. Work on home wiring must be done by a licensed electrician. Read our disclaimer.
When this tool helps most
Use it before connecting a generator to your home. It compares interlock kits, manual transfer switches and automatic switches for your setup.
Common mistakes to avoid
- Backfeeding through a dryer or wall outlet.
- Buying an interlock kit that is not listed for your panel.
- Mismatching the inlet, cord and generator outlet amperage.
Understanding your result
The selector suggests a connection type; a licensed electrician confirms it fits your panel, pulls any permit and installs it.
How to get the most accurate result
- Use numbers from your own appliance labels, manuals, bills and quotes instead of averages.
- Change one input at a time to see which assumption matters most.
- Save or print the result and bring it to your electrician or installer.
- Re-run the tool when your rates, appliances or plans change.
Step-by-step guides that use this tool
These guides explain the decisions behind the numbers, so you can act on your result with confidence.