Understand the terms
A transfer switch isolates the utility supply from the generator supply and selects which source feeds a home circuit or panel. A manual transfer switch requires a person to make the change. An automatic transfer switch (ATS) can detect a utility outage and change sources when used with a compatible standby generator and controls.
A panel interlock kit is a mechanical accessory designed for a particular panel configuration. It allows the generator breaker to be operated only when the corresponding utility main breaker is in the required off position. It is not a universal substitute for any transfer switch or panel accessory.
The names are sometimes used loosely in product listings. Confirm the exact device, listing, panel compatibility, circuit coverage, and operating method in the quote.
Manual transfer switch vs. panel interlock
| Question | Manual transfer switch | Panel interlock kit |
|---|---|---|
| What does it do? | Selects utility or generator source for the circuits covered by the switch. | Physically constrains the compatible panel breakers so the sources cannot be connected together in the intended configuration. |
| How is it operated? | The homeowner manually switches the named circuits after following the equipment instructions. | The homeowner follows the exact panel/interlock instructions and selects the approved generator-fed circuits. |
| Circuit selection | Usually limited to the circuits wired through the switch; exact capacity varies by device. | Uses compatible breakers in the existing panel; load limits and breaker arrangement depend on the panel and generator. |
| Panel compatibility | Must be appropriate for the service, generator, and selected circuit arrangement. | Must be specifically listed or approved for the exact panel model and configuration. |
| Automatic operation? | No. A separate ATS is a different device and system configuration. | No. The owner operates it manually. |
| What determines cost? | Device type/rating, circuits, wiring route, labor, permitting, and service scope. | Panel compatibility, the listed interlock and breaker, inlet/routing work, labor, permitting, and any needed panel changes. |
An automatic transfer switch for a permanently installed standby unit is a third arrangement. Do not compare its price or capabilities to a manual switch/interlock without matching amperage, service-entrance rating, circuits, and included work.
Backfeed is the hazard to prevent
Connecting generator power to household wiring without correctly installed transfer equipment can energize utility wiring and endanger utility workers, neighbors, or occupants. CPSC explicitly warns never to power house wiring by plugging a generator into a wall outlet; it also says this can bypass household circuit protection. ESFI likewise recommends appropriate transfer equipment. Never use a “suicide cord,” dryer outlet, or improvised connection.
This page is not wiring instruction. A qualified electrician must determine whether a transfer switch or a panel-specific interlock is permitted for the exact equipment and local jurisdiction, select compatible listed equipment, and complete any required permit and inspection.
Questions for a qualified electrician
- Which exact generator, inlet, transfer equipment, panel, and breaker models are included?
- Is the proposed interlock or switch listed/approved for this exact panel and service arrangement?
- Which loads can be energized together, and how will the homeowner know what to shed?
- Do the generator’s neutral/grounding arrangement and transfer equipment require specific configuration?
- What permit, inspection, labeling, operating instructions, and commissioning are included?
- Will panel condition or capacity require repairs or replacement before the work is approved?
Request an itemized written quote; scope, not a device label alone, determines cost. See our transfer-switch cost guide for planning factors, and follow the generator, switch, and panel manufacturers’ current instructions.