Solar, Batteries & Backup Power
Transfer Switches & Interlocks Explained
A transfer switch keeps generator power and utility power from meeting. It's the piece that makes backup power safe.
Updated 2026-10-15
Why it's required
Connecting a generator without isolation can backfeed the utility transformer, energizing lines that crews believe are dead. That's why plugging a generator into a dryer outlet with a double-male cord is dangerous and illegal. Code requires a listed transfer means.
Your options
From simplest to most automated:
- Interlock kit: a mechanical plate that prevents the main and generator breakers from being on at once
- Manual transfer switch: selects specific circuits for generator power
- Automatic transfer switch (ATS): senses an outage, starts the generator, and transfers load
- Service-rated ATS with load shedding for whole-home systems
Portable generators
For portable units, an interlock with a properly rated inlet box is a cost-effective, code-compliant setup. Keep the generator outdoors, well away from doors and windows, to avoid carbon monoxide exposure.
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Frequently asked questions
Is an interlock kit legal?
Listed interlock kits approved for your panel are accepted in most jurisdictions. Confirm with your electrician and local inspector.
Can a transfer switch power my whole house from a portable generator?
It can connect the whole panel, but you must manage loads manually so you don't exceed the generator's capacity.
Does the utility need to know?
Some utilities ask to be notified about standby generators; all require that they be isolated from the grid.
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This guide is general information, not engineering or legal advice. Electrical codes are adopted and amended locally — consult a licensed electrician and your local building department for your project.