Best Generator Transfer Switches and Interlock Kits
The best generator transfer switches and interlock kits for portable generators: 6 vs 10 circuits, 30A vs 50A, and which setup suits your panel.
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The short answer
For most homes using a portable generator up to about 7,500 running watts, the Reliance Controls 31406CRK 6-circuit, 30-amp transfer switch kit is the best all-round choice, and the 31410CRK 10-circuit version is the pick if you want to back up more circuits. If your panel has room and you want to power any circuit in the house, a panel interlock kit paired with a 30- or 50-amp power inlet box is the lower-cost, more flexible route. Either way, have a licensed electrician install it and pull the permit your town requires.
Our top picks
- Best overall: Reliance Controls 31406CRK — A 6-circuit, 30-amp kit for portables up to about 7,500 running watts. Check price on Amazon
- Best for more circuits: Reliance Controls 31410CRK — The 10-circuit version for backing up more of the house. Check price on Amazon
- Best interlock for GE panels: GE-compatible interlock kit — The lower-cost route that can power any circuit in the panel. Check price on Amazon
Not sure what size you need? Tick your appliances in our generator size calculator and get a recommended wattage in seconds.
Why you need one (and why “backfeeding” is dangerous)
Plugging a generator into a dryer outlet with a double-male cord sends power backward into your panel and, unless the main breaker is off, out onto the utility lines, where it can electrocute line workers. It can also energize your wiring in ways that start fires. A transfer switch or interlock makes it physically impossible to have utility power and generator power connected at the same time. Many local codes require one, and generator manufacturers say the same in their manuals.
Transfer switch vs. interlock kit
| Manual transfer switch | Panel interlock kit | |
|---|---|---|
| How it works | A small sub-panel next to your main panel; you move selected circuits to generator power with switches | A sliding plate on your main panel that lets the generator breaker turn on only when the main breaker is off |
| Circuits you can power | Only the 6–10 you pre-wire | Any circuit in the panel (you manage the load by switching breakers) |
| Parts cost | Higher | Lower (kit + a 2-pole breaker + inlet box) |
| Panel compatibility | Works with most panels | Must match your panel brand, model and amp rating, and needs open space near the main breaker |
| Ease during an outage | Simple: flip labeled switches, wattmeters on some models | Requires turning off the main and managing breakers yourself |
| Best for | Owners who want a simple, guided setup | Owners with a compatible panel who want whole-panel flexibility |
Our picks at a glance
| Pick | Product | Type | Rating | Best for | Amazon |
|---|---|---|---|---|---|
| Best overall | Reliance Controls 31406CRK | 6-circuit manual transfer switch kit | 30A, generators up to 7,500 running watts | Essentials: fridge, furnace, well pump, lights | Check price |
| Best for more circuits | Reliance Controls 31410CRK | 10-circuit manual transfer switch kit | 30A | Larger homes with more circuits to cover | Check price |
| Best interlock (GE panels) | GE-compatible interlock kit | Panel interlock | For GE 150/200A main-breaker panels | Whole-panel flexibility on GE panels | Check price |
| Best interlock (Siemens/Murray) | Siemens/Murray-compatible interlock | Panel interlock | For Siemens and Murray main-breaker panels | Whole-panel flexibility on those panels | Check price |
| Best inlet box | Reliance Controls PB30 | 30A power inlet box (L14-30) | Up to 7,500 running watts | Pairs with either option | Check price |
| Best for power stations | Nature’s Generator 30A 6-circuit transfer switch | 6-circuit manual transfer switch | 120V, 30A | Battery backup instead of gas | Check price |
How we picked
We compared manufacturer specifications, electrical-code guidance, installation manuals and owner reviews. We weighted amp rating relative to common portable generators, how many circuits each option covers, how easy it is to use in the dark during an outage, and whether the product is a well-established part that electricians and inspectors recognize.
1. Reliance Controls 31406CRK — Best overall
The Pro/Tran 31406CRK is the transfer switch most electricians have installed many times. It’s a 30-amp, 6-circuit unit that mounts beside your main panel, with a pre-wired whip that connects to the circuits you choose. Each circuit gets its own Line/Off/Generator switch, so during an outage you plug the generator into the inlet, start it, and move the circuits over one by one. It is designed for generators up to 7,500 running watts, which matches the 30-amp L14-30 outlet on most large portables.
Good to know: six circuits fills up fast. A 240V well pump or water heater uses two of them. List your must-run circuits before you choose between 6 and 10.
Check the Reliance Controls 31406CRK on Amazon →
2. Reliance Controls 31410CRK — Best for more circuits
The 31410CRK is the same Pro/Tran design with 10 circuits. That’s enough for a fridge, freezer, furnace blower, well pump, sump pump, kitchen and bedroom lights and a few outlets in a typical house. It is still a 30-amp switch, so the total load is capped by your generator, but the extra circuits make it easier to rotate what’s running.
Good to know: more circuits doesn’t mean more power. You still need to keep the combined load under the generator’s running watts.
Check the Reliance Controls 31410CRK on Amazon →
3. GE-compatible interlock kit — Best interlock for GE panels
An interlock kit is a steel plate that bolts to your panel cover. When the main breaker is on, the plate blocks the generator breaker; to power the house from the generator, you switch the main off, slide the plate, and switch the generator breaker on. This listing is a third-party kit made for GE 150- and 200-amp main-breaker panels. You also need a 2-pole breaker in the top-right slot (typically 30A for an L14-30 inlet) and an inlet box outside.
Good to know: interlock kits are panel-specific, and some inspectors want a kit that is listed for your exact panel. Confirm with your electrician and local building department before buying.
Check the GE-compatible interlock kit on Amazon →
4. Siemens/Murray-compatible interlock — Best for Siemens panels
Siemens sells its own interlock under part number ECSBPK02, and compatible kits are widely available for Siemens and Murray main-breaker panels. Functionally it’s the same idea: whole-panel flexibility for much less than a transfer switch, as long as your panel matches.
Good to know: measure the spacing between the main breaker and the first branch breaker and match it to the kit’s spec; that dimension decides whether an interlock will fit.
Check the Siemens/Murray interlock on Amazon →
For other panel brands (Square D, Eaton/Cutler-Hammer), search by your panel’s model number: Square D interlock kits or Eaton interlock kits.
5. Reliance Controls PB30 — Best power inlet box
Whatever you choose, the generator connects to the house through an outdoor inlet box, not through a window. The PB30 is a 30-amp, NEMA 3R weather-resistant box with an L14-30 inlet, rated for generators up to 7,500 running watts. It’s the standard match for a 30-amp transfer switch or interlock. If your generator has a 50-amp outlet and you plan to use it, choose a 50-amp inlet and switch instead.
Check the Reliance PB30 on Amazon →
6. Nature’s Generator 30A 6-circuit transfer switch — Best for power stations
If you’re backing up with a large battery power station rather than a gas generator, you still need a safe way into your panel. Nature’s Generator’s UL-listed manual transfer switch is rated for 30 amps at 120V across six circuits, and the maker lists it as compatible with lithium power stations and solar generators as well as gas and dual-fuel generators. It comes pre-wired with an L5-30P inlet and a 30A cord, and illuminated rocker switches show which circuits are on backup power.
Good to know: it’s a 120V setup, so it won’t run 240V loads like a well pump. Confirm your power station has a matching 30A outlet, and have a licensed electrician install it.
Check the Nature’s Generator 30A transfer switch on Amazon →
Sizing: 30-amp or 50-amp?
| Generator outlet | Typical running watts | Switch/inlet to match |
|---|---|---|
| L14-30 (30A, 120/240V) | Up to about 7,500W | 30A transfer switch or interlock + 30A inlet |
| 14-50 or CS6365 (50A, 120/240V) | About 7,500–12,000W | 50A transfer switch or interlock + 50A inlet |
| L5-30 / TT-30 (30A, 120V only) | Up to about 3,600W | 120V-only setups; won’t run 240V loads |
Match the switch to the generator outlet you’ll actually use. A big generator like the Westinghouse WGen9500DF has both 30A and 50A outlets, so you can choose either path.
Buying and installation checklist
- List your must-run circuits and add up their running and starting watts.
- Check your panel brand, model and amp rating before buying an interlock; take a photo of the label for your electrician.
- Match amps: switch, inlet, cord and generator outlet should all be the same rating.
- Buy a proper cord: a heavy-gauge L14-30 generator cord long enough to keep the generator at least 20 feet from the house.
- Permits and inspection: required in many areas, and your homeowner’s insurance may care.
- CO safety: run generators outdoors only, away from doors, windows and vents, and install CO alarms inside.
FAQ
Is an interlock kit as safe as a transfer switch?
When it’s listed for your panel and installed correctly, an interlock provides the same protection against backfeeding: the generator breaker cannot be on while the main breaker is on. Some jurisdictions have specific rules, so check locally.
Can I install a generator transfer switch myself?
It involves working inside your main panel, and many areas require a licensed electrician and a permit. Hiring an electrician is the safe choice.
How many circuits do I need on a transfer switch?
Six circuits covers essentials in a smaller home; ten is better if you have a well pump, sump pump and several rooms to light. Remember 240V loads use two circuits.
Do I need a 30-amp or 50-amp transfer switch?
Match the generator outlet you will use. A 30A L14-30 setup suits generators up to about 7,500 running watts; larger generators with a 50A outlet can use a 50A switch or interlock.
Is it legal to backfeed a dryer outlet with a generator?
No. Backfeeding without a transfer switch or interlock violates electrical codes and can electrocute utility workers. Always use an approved transfer device.
