Connecting a generator to your house seems straightforward until you realize that doing it wrong can kill someone. Specifically, it can kill a utility worker who’s repairing power lines, assuming those lines are dead. This phenomenon — called backfeed — is why every method of connecting a generator to your home’s electrical system requires a device that physically prevents generator power from reaching the utility grid. No exceptions, no shortcuts, no “just this once.”
As an electrical engineer, I’ve installed transfer switches and interlock kits on dozens of homes. There are exactly three safe ways to get generator power into your house, ranging from simple (extension cords) to professional (automatic transfer switch). Here’s how each works, what they cost, and which one is right for your situation.
Method 1: Extension Cords (Simplest, No Installation)
How It Works
Run heavy-duty extension cords from the generator’s outlets directly to individual appliances inside your home. The generator stays outside (at least 20 feet from the house), and cords run through a cracked window or door to reach appliances.
Pros
Cons
Best Practices
Best For
Renters, occasional use, budget-conscious homeowners, or anyone who only needs to power plug-in appliances (refrigerator, space heater, lamps, electronics).
Method 2: Manual Transfer Switch ($700-1,500 Installed)
How It Works
A manual transfer switch is installed next to your main electrical panel by a licensed electrician. It connects to specific circuits in your panel (typically 6-10 circuits) and provides a switching mechanism that transfers those circuits between utility power and generator power. A power inlet box is mounted on the exterior of your house, and you connect the generator to this inlet with a heavy-duty cord (called a generator cord or genset cord).
The transfer process:
- Start the generator and let it warm up
- Plug the generator cord into the power inlet box
- At the transfer switch, flip each circuit switch from “Line” (utility) to “Gen” (generator)
- Selected circuits now receive generator power through your home’s existing wiring
- When utility power returns, flip switches back to “Line” and shut down the generator
Pros
Cons
Popular Transfer Switch Brands
Best For
Homeowners with portable generators who want to power hardwired circuits (furnace, well pump, sump pump) safely and conveniently. This is the most popular connection method for portable generators.
Method 3: Interlock Kit ($250-600 Installed)
How It Works
An interlock kit is a mechanical device that mounts on your existing electrical panel. It’s a sliding metal plate that physically prevents the main breaker and a dedicated generator breaker from being turned on simultaneously. When you slide the interlock to enable the generator breaker, the main breaker must be off — disconnecting your home from the utility grid and preventing backfeed.
The transfer process:
- Start the generator and connect it to the power inlet box
- Turn OFF the main breaker
- Slide the interlock plate to allow the generator breaker to turn on
- Turn ON the generator breaker
- Turn on individual circuit breakers as needed (managing total load to stay within generator capacity)
- When utility power returns, reverse the process: turn off generator breaker, slide interlock, turn on main breaker
Pros
Cons
Best For
Homeowners who want whole-panel access on a budget, are comfortable managing loads manually, and have a compatible electrical panel. Particularly good for larger generators (7,500W+) where you want flexibility to power different circuits at different times.
What About Automatic Transfer Switches?
Automatic transfer switches (ATS) are primarily used with standby generators. They detect utility power failure, signal the generator to start, and transfer the load automatically — no human intervention required. For portable generators, an ATS isn’t practical because someone still needs to go outside, start the generator, and connect the cord. Manual transfer switches and interlock kits are the appropriate solutions for portable generators.
If you want fully automatic backup power, the solution is a standby generator with an integrated ATS — a different category of product entirely, with installed costs of $7,000-15,000+.
The Generator Cord (Power Inlet Setup)
Both transfer switches and interlock kits require a power inlet box and generator cord:
Power Inlet Box
A weatherproof box mounted on the exterior of your house, typically near the electrical panel. It has a twist-lock receptacle that accepts the generator cord. The inlet box is wired through the wall to the transfer switch or generator breaker inside. Installation requires drilling through the exterior wall and running appropriate gauge wire.
Generator Cord
A heavy-duty cord (typically 30A or 50A, 10-gauge or 6-gauge) with twist-lock plugs on both ends — one end connects to the generator’s 240V outlet, the other to the power inlet box. Cord length is typically 20-30 feet. Use the shortest cord that reaches from your generator placement to the inlet box to minimize voltage drop.
Important: The generator cord must match the amperage of your transfer switch or generator breaker. A 30A transfer switch requires a 30A cord. A 50A setup requires a 50A cord. Mismatched amperage creates fire hazards.
What You Must NEVER Do
The “Suicide Cord” (Male-to-Male Plug)
A male-to-male extension cord (also called a “suicide cord” or “backfeed cord”) has exposed prongs on both ends. People use them to plug a generator into a wall outlet, backfeeding power through the home’s wiring. This is:
There is no scenario where a suicide cord is acceptable. If someone suggests it, they’re giving you dangerous advice. The cost of a proper transfer switch or interlock kit ($250-1,500) is trivial compared to the liability of killing a utility worker or burning down your house.
Installation Considerations
Permits and Inspections
Most jurisdictions require an electrical permit for transfer switch or interlock kit installation. The work must be performed by (or at minimum inspected by) a licensed electrician. After installation, an electrical inspector verifies the work meets code. Don’t skip this step — unpermitted electrical work can void your insurance and create liability issues.
Generator Sizing
Your transfer switch or interlock kit should match your generator’s output. A 30A/7,500W generator pairs with a 30A transfer switch and 30A inlet. A 50A/12,000W generator pairs with a 50A setup. Oversizing the transfer switch beyond your generator’s capacity doesn’t provide any benefit and may mask overload conditions.
Inlet Box Placement
Place the power inlet box on the exterior wall closest to where you’ll position the generator. Keep the generator cord as short as possible (20-25 feet is ideal). The inlet should be at least 18 inches above grade and protected from direct rain exposure. Consider which side of the house is most sheltered from prevailing storm winds.
Frequently Asked Questions
Q: Can I install a transfer switch myself?
Technically, a knowledgeable homeowner with electrical experience can install a transfer switch. However, it involves working inside your main electrical panel with live utility wires — this is dangerous and, in most jurisdictions, requires a licensed electrician and a permit. The risk of electrocution, improper wiring, or code violations makes professional installation strongly recommended. The $500-1,000 installation cost is money well spent for safety and code compliance.
Q: How do I know if an interlock kit fits my panel?
Interlock kits are panel-specific — they’re designed for specific brands and models. Check the label inside your panel door for the manufacturer (Square D, Siemens, Eaton/Cutler-Hammer, GE, etc.) and model number. Interlock kit manufacturers like GenInterlock and Reliance Controls have compatibility charts on their websites. If your panel is very old or an uncommon brand, an interlock kit may not be available, and a transfer switch is your best option.
Q: Do I need a 30A or 50A transfer switch?
Match the transfer switch to your generator’s largest outlet. Most portable generators under 7,500W have a 30A/240V outlet — use a 30A transfer switch. Generators over 7,500W typically have a 50A/240V outlet — use a 50A transfer switch. If your generator only has 120V outlets (no 240V), you’ll need a transfer switch designed for 120V-only connection, or you’ll need to upgrade to a generator with a 240V outlet.
Q: Can I power my whole house with a transfer switch?
A manual transfer switch powers only the circuits connected to it (typically 6-10). An interlock kit gives access to all circuits in your panel, but you’re still limited by the generator’s output — you can’t run all circuits simultaneously unless your generator is large enough. In practice, you select the most important circuits and manage loads to stay within your generator’s capacity.
The Bottom Line
For occasional use with plug-in appliances only, extension cords work fine. For powering hardwired circuits (furnace, well pump, sump pump), you need either a manual transfer switch ($700-1,500 installed) or an interlock kit ($250-600 installed). Both are safe, code-compliant, and prevent deadly backfeed. The transfer switch is simpler to operate; the interlock kit is cheaper and provides whole-panel access. Either way, hire a licensed electrician, pull a permit, and never use a suicide cord. Your safety and your neighbors’ safety depend on it.
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