The question of how to actually get generator power into a house separates everyone who buys a portable generator into three camps: people who run extension cords through a cracked window, people who installed a transfer switch or interlock the first weekend they owned the generator, and people who're stalling because they think it's complicated. This piece is for the third group.
There are three legal ways to do this. The right answer for your situation depends on how much of the house you want to power and how often you expect to use the generator. None of them are conceptually hard. All of them are within reach of a typical electrician for under $1,200 total installed.
Method 1: Extension cords
The simplest approach. Run heavy-gauge outdoor extension cords from the generator outside to whichever individual appliances you want to power — fridge, lamps, fans, electronics, a window AC. No wiring work. No permit. Works the day you get the generator home.
What you need: 12-gauge or 10-gauge outdoor-rated extension cords, sized for the run length and load. For a 20-foot run powering a fridge + a few lamps + electronics, a 12-gauge SJTW cord rated 15 amps is fine. For longer runs or larger loads, step up to 10-gauge.
What you can't power this way: anything hardwired into the panel. That means furnace, well pump, central AC, electric water heater, hardwired sump pumps. For most outages, what you can run is enough — keep the food cold, charge devices, watch the news, maintain communication. For longer outages, especially in cold weather where furnace operation matters, you'll want a panel-level connection.
Pros: Zero install cost. No permit. Immediately usable.
Cons: Limited to what you can plug into a cord. Cords running through doors create CO infiltration paths. Tripping hazard.
Method 2: Manual transfer switch
A manual transfer switch is a panel-mounted device that physically disconnects selected circuits from the utility grid and reconnects them to a generator inlet. The switch can only be in "utility" or "generator" position, never both — that's what prevents backfeed. Six to ten circuits is typical for a residential install (the most common is the Reliance Pro/Tran 6 or 10).
How it works in practice: you choose which circuits you want to be on backup power — fridge, furnace blower, kitchen counter outlets, a few bedroom outlets, the panel feeds to those circuits — and the electrician wires them through the transfer switch. During an outage, you plug the generator into an inlet box mounted on the exterior of the house, flip the transfer switch from "utility" to "generator," and the selected circuits come alive while the rest of the panel stays disconnected from both grid and generator.
Cost: $600 to $1,200 fully installed, including switch ($250–350), inlet box ($60–100), generator cord ($60–150), permit fees ($50–150), and electrician labor (3–5 hours at typical rates). Permanent install — works for any future generator within wattage range.
What you'll need from the generator side: an L14-30 outlet (30A, 240V four-prong twist-lock) for a 7,500W or smaller unit, or an L14-50 (50A, 240V) for larger units. Almost every dual-fuel generator at 5,000W+ has the L14-30; bigger generators have both.
Pros: Code-compliant nationwide. Can power hardwired circuits (furnace, sump pump, hardwired well pump). Permanent install — no setup in an outage. Sells with the house.
Cons: Upfront cost. Limited to the circuits you wire through it (usually 6–10).
Method 3: Generator interlock kit
An interlock kit is a metal slide mounted on your panel cover that physically prevents the main breaker and a dedicated generator-feed breaker from being on at the same time. When you want to switch to generator power, you flip the main breaker off, slide the interlock, and flip the generator-feed breaker on. The mechanical interlock makes it impossible to have both breakers on simultaneously.
This is functionally equivalent to a transfer switch but cheaper and works at the panel level rather than the circuit level — meaning any circuit in the panel can be powered (within the generator's wattage limit). You manage load by turning off non-essential breakers manually when running on generator power.
Cost: $400 to $700 installed. The kit itself is $80–150 (typically panel-specific — Square D QO, Siemens, Cutler-Hammer/Eaton, GE — must match your panel). Generator inlet box and cord same as the transfer-switch route. Electrician labor 2–3 hours.
Code status: permitted in most jurisdictions and required by NEC 702.5 to be listed for use with the specific panel. A few municipalities require a transfer switch instead — check before assuming. The installation requires a permit and inspection in most places.
Pros: Cheaper than a transfer switch. Can power any circuit (subject to wattage). Doesn't take up additional wall space.
Cons: Requires panel-specific kit. Manual load management — you'll trip breakers if you don't turn off non-essentials. Not allowed in all jurisdictions.
Generator inlet boxes
For both methods 2 and 3, you need a "power inlet box" — an outdoor-rated receptacle on the exterior wall of the house that accepts the generator cord. The most common is the Reliance PB30 (30A) or PB50 (50A). The inlet box is wired through the wall to the transfer switch or generator-feed breaker. Cord runs from generator to inlet box during operation.
Mount the inlet box near the panel for a short interior cable run, but at a height and location that lets the cord reach where you'll position the generator outside — 20 feet minimum from any door, window, or vent.
The illegal method (don't)
The "suicide cord" — an extension cord with male plugs on both ends, plugged into a generator on one end and a dryer outlet on the other — is a method that some people use and that occasionally kills line workers, homeowners, or both. It's illegal in every US jurisdiction and against generator manufacturer instructions. We covered why in detail in generator safety: CO and backfeeding. There is no "I just open the main breaker first" workaround that makes it safe; the main breaker can be defeated by a family member, fail mechanically, or be re-closed by accident.
Which method to choose
| Scenario | Best method |
|---|---|
| Rare outage, just keep the fridge cold | Extension cords |
| Annual outages, want to run furnace + fridge + lights | Manual transfer switch (or interlock kit) |
| Frequent outages or rural location with well water | Interlock kit (panel-level coverage) |
| Plan to upgrade to standby (whole-house) later | Skip portable connection; price standby instead |
| Renter or short-term residence | Extension cords |
What to ask the electrician
- What's the wattage of the largest generator I might ever own here? (Sizes the inlet box and breaker.)
- Is interlock approved in this jurisdiction, or do you have to use a transfer switch?
- What's the permit cost and inspection process?
- What location on the exterior wall makes sense for the inlet box?
- If transfer switch — which circuits should we wire through it?
A competent electrician will walk through these in one visit, give a written quote, and have the job done in a Saturday. Pull the permit, pass inspection, and you're set up for every outage for as long as you own the house.
Frequently Asked Questions
Can I install a transfer switch or interlock kit myself?
Legally, in most jurisdictions, no — panel work requires a licensed electrician and a permit. Some jurisdictions allow homeowner-permitted work in their own residence. Even where it's legal, panel work is one of the worst places to learn DIY: a mistake can kill you, start a fire, or void your home insurance. The cost of hiring an electrician is small compared to the consequences of getting it wrong.
Will a transfer switch work with any generator?
Yes, within wattage limits. A transfer switch rated for 30A (7,200W at 240V) accepts any generator with an L14-30 output and the right cord. A 50A transfer switch accepts up to 12,000W generators with L14-50. The switch doesn't care about the generator brand.
How long does it take to switch over to generator power?
With a transfer switch or interlock kit: about 60–90 seconds, including starting the generator, plugging in the cord, and flipping the breakers. Fast enough that you can switch over before perishable foods warm up.
Do I need a 240V generator to power my house?
If you want to power 240V circuits (well pump, central AC, electric water heater, electric range, electric dryer), yes — you need a generator with 240V output, typically L14-30 (7,500W class) or L14-50 (12,000W+). If you only need 120V circuits (fridge, lights, electronics, gas furnace blower), a 120V-only generator works with a smaller transfer switch.
Will my home insurance care about how the generator is connected?
Most home insurance policies require that any permanent electrical work be done to code and permitted. An unpermitted DIY transfer switch installation could void coverage on a claim related to the panel, electrical fire, or backfeed incident. Pull the permit, keep the documentation — your insurance company may ask.