A portable generator sitting in the yard is only half of a backup power system. The other half is a safe way to get its electricity to the things you want to run. There are three legitimate options, from a handful of extension cords to a permanently installed inlet and transfer switch. This guide explains each one, what it can and cannot power, and why the shortcut you may have heard about is dangerous.
Quick answer
For a few appliances, run outdoor-rated extension cords straight from the generator. To power hard-wired circuits such as a furnace, well pump or lights, have a licensed electrician install a power inlet box on an outside wall and either a manual transfer switch or an interlock kit at your electrical panel. Never feed the house through a wall or dryer outlet.
In this guide
Option 1: Extension cords
The simplest method. Plug appliances directly into the generator with heavy-duty cords run through a window or door that can still be closed on the cord, or through a purpose-made cord pass-through.
- Use outdoor-rated cords with three prongs and a wire gauge heavy enough for the load. For a refrigerator or space heater on a 50-foot run, 12-gauge is the minimum; use 10-gauge for longer runs or heavier loads.
- Check the cord rating against the appliance: a cord rated for 15 amps carries 1,800 watts at 120 volts.
- Inspect cords every time for cuts, crushed insulation and bent prongs.
- Keep connections dry and off the ground.
Pros
- No installation, works anywhere
- Lowest cost
- Nothing to permit or inspect
Cons
- Cannot power a furnace, well pump, ceiling lights or anything hard-wired
- Cords through doors and windows let in cold and water
- Easy to overload a single cord
Option 2: Manual transfer switch
A manual transfer switch is a small sub-panel installed next to your main panel. The electrician moves a handful of chosen circuits, typically six to ten, into it: furnace, well pump, refrigerator, a few lights and outlets. A power inlet box on the outside wall connects to the switch. During an outage you plug the generator into the inlet with a single heavy cord, start it, and flip the switch from utility to generator. Each circuit has its own breaker, so you can see what is on.
Transfer switches are rated by amperage, commonly 30 A (up to 7,200 watts from a 120/240 V generator) or 50 A (up to 12,000 watts). Choose one that matches the 240 V outlet on your generator: an L14-30 outlet pairs with a 30 A switch, a 14-50 outlet with a 50 A switch.
Pros
- Powers hard-wired circuits, including the furnace and well pump
- Impossible to backfeed
- Clear view of which circuits are live
- Widely understood by inspectors
Cons
- Limited to the circuits moved into the switch
- Costs more than an interlock
- Needs a permit and a licensed electrician
Option 3: Interlock kit with an inlet box
An interlock is a sliding metal plate fitted to your existing main panel. It makes it physically impossible to switch on the generator breaker unless the main utility breaker is off, and vice versa. The generator feeds the whole panel through a dedicated backfeed breaker connected to the outside inlet box, and you choose which circuits to run by switching the others off.
Because the generator feeds the entire panel, you must manage the load yourself. Switch off the big 240 V circuits (range, dryer, water heater, air conditioning) before starting, then bring circuits on one at a time. Interlock kits must be listed for your specific panel model, and some jurisdictions do not allow them, so ask the electrician first.
Pros
- Any circuit in the house can be used
- Less expensive than a transfer switch
- Compact: no extra panel
Cons
- You must manage the load manually to avoid overloading the generator
- Kit must match your panel exactly and be allowed locally
- Needs a permit and a licensed electrician
What the installed setup involves
- Power inlet box. Mounted outside, rated to match the generator outlet (30 A L14-30 or 50 A 14-50).
- Generator cord. A 10-gauge cord for 30 A, 6-gauge for 50 A, in a length that lets the generator sit at least 20 feet from the house. Longer is fine; thinner is not.
- Transfer switch or interlock at the panel, with the backfeed breaker.
- Permit and inspection, which the electrician usually handles.
- Neutral bonding check. Portable generators have either a bonded or a floating neutral. The electrician will confirm which yours has and set up the system to suit it. This matters for safety and for GFCI outlets working correctly.
Using it during an outage
- Wheel the generator outside, at least 20 feet from the house, with the exhaust pointing away from doors, windows and vents.
- Switch off the main breaker (or the generator-side breakers), then connect the cord to the inlet and the generator.
- Start the generator and let it warm up for a minute or two.
- Transfer to generator power. On an interlock, flip the main off and the generator breaker on.
- Bring circuits on one at a time, largest motor first.
- When utility power returns, transfer back to the utility, then shut the generator down and let it cool before refueling.
Which option is right for you?
| If you want to | Choose |
|---|---|
| Run a refrigerator, a few lights and chargers in a rare outage | Extension cords |
| Power a furnace or well pump without touching the rest of the house | Manual transfer switch |
| Choose freely among all circuits and keep the cost down | Interlock kit, if allowed locally |
| Forget about it entirely and have the house switch over on its own | A standby generator with an automatic transfer switch |
Frequently asked questions
Can I connect a generator to my house without a transfer switch?
Safely, only with extension cords to individual appliances. An interlock kit is an alternative to a full transfer switch for powering circuits, but it still needs a proper inlet, a backfeed breaker and installation by an electrician. There is no safe way to feed house wiring through an ordinary outlet.
Do I need a permit to install a generator inlet?
In most places, yes. The work involves your electrical panel, and inspectors want to confirm that the house cannot be connected to the generator and the grid at the same time. The electrician normally pulls the permit.
Does my generator need to be grounded?
Follow the manual. Most portable generators used with cord-connected appliances and a properly installed transfer switch do not need a separate ground rod, because the frame serves as the ground. Some installations and local codes do require one, which is another reason to involve an electrician.
Can an interlock kit damage my electrical panel?
Not if it is listed for that exact panel and installed correctly. Generic or ill-fitting kits are the problem, and they are the reason some inspectors refuse them. Buy the kit made for your panel model.
