How to Connect a Generator to Your House Safely

This is the only way to use a generator with your house without a transfer switch or interlock. Run a heavy outdoor cord from the generator to each appliance and plug it in directly. Use 12 gauge for 50 ft runs and 10 gauge for motor loads like a sump pump, so voltage drop stays low. Thin 16 gauge cords overheat and starve motors.

A fan cord saves clutter. If your generator has a 120 V 30 A twist-lock outlet, one 25 ft fan cord brings three household outlets to the back door. Do not prop a door or window open for the cords, since that lets exhaust in. Cords cannot reach a furnace, a well pump or anything hardwired, which is where the next two options come in.

An interlock is the cheapest legal way to feed your breaker panel. An electrician mounts a sliding plate on the panel cover, adds a 30 A two-pole breaker in the top slot, and wires it to an outdoor inlet box. A 30 A cord runs from the generator's L14-30R outlet to that inlet. Parts come to about $220, and the electrician typically charges $300 to $800 depending on region and how far the inlet sits from the panel.

You get the whole panel. On outage day you choose which circuits to switch on, as long as the total stays under the generator's running watts and under 7,200 W, the limit of a 30 A, 240 V connection. Kits are panel-specific, so read the label inside your panel door for brand, series and amperage before ordering.

Most portable generators ship with the neutral bonded to the frame, and neither an interlock nor this style of transfer switch switches the neutral. Some inspectors want that bond removed for a panel connection. Ask your electrician to check it when the permit is pulled.

A transfer switch is a small subpanel beside your main panel with one switch per circuit, each set to line, off or generator. The Reliance 31410CRK covers 10 circuits and ships with the inlet box and a 10 ft cord. Parts run $250 to $500 and installation is similar to an interlock, so expect $700 to $1,200 all in.

Pick it over an interlock when your panel has no matching interlock kit, when the panel is full, or when someone else in the house will run the generator. Each switch is labeled, and you never touch the main breaker. The trade-off is that only the 10 wired circuits can run on generator power.

A double-male cord into a dryer or range outlet is often called a suicide cord, and the name is earned. With the main breaker on, generator power flows out through your meter and the utility transformer steps it up to thousands of volts on the street line. A lineworker who expects a dead wire can be killed, and lineworkers have died this way.

It also endangers you. The exposed prongs are live the moment the engine runs. When grid power returns, two unsynchronized sources meet in your panel, which can destroy the generator and start a fire. It violates the National Electrical Code, insurers can deny the claim, and many utilities pull the meter when they find one.

Hire a licensed electrician and pull a permit for any panel connection. An interlock or transfer switch costs less than one burned-out generator.

Step 1. Roll the generator outside, at least 20 feet from the house with the exhaust pointed away from doors and windows. Never run it in a garage, carport or crawl space, even with the door open. Check that the battery CO alarms on each sleeping level work.

Step 2. Turn off the main breaker. Then switch off every branch breaker so nothing starts at once when the generator comes on.

Step 3. Slide the interlock plate so the generator breaker can turn on. The main is now locked off.

Step 4. Plug the L14-30 cord into the generator and into the inlet box, then start the generator and let it run for a minute or two with no load.

Step 5. Turn on the generator breaker in the panel. Then turn on circuits one at a time, starting with the biggest motor, such as the well pump, fridge or furnace. Give each one a few seconds to start before adding the next, and stay under the generator's running watts.

Step 6. To refuel, turn off the generator breaker, shut the engine down and let it cool before adding fuel. Spilled gas on a hot muffler starts fires.

Step 7. When the grid comes back, turn off the generator breaker, slide the plate back, turn the main on, then stop the generator and unplug the cord. Our generator fuel calculator tells you how many gallons or propane tanks to stock for a long outage.

For an interlock or the Reliance kit, you need a generator with an L14-30R 120/240 V outlet. That outlet is what makes 240 V loads like a well pump possible. All three below have it. Run your loads through the generator sizer first so you buy the right size, not the biggest one.