How do you hook up a portable generator to your house?
You connect it through a transfer switch or a breaker interlock plus an outdoor inlet box, installed by a licensed electrician, normally under a permit, and the job usually costs $400 to $1,300.
You hook a portable generator to your house through a transfer switch, or through a breaker interlock kit plus an outdoor generator inlet box. A licensed electrician installs either one, normally under a permit. In 2026 guides put the job at about $400 to $1,300 for a standard manual transfer switch and about $400 to $850 for an interlock with an inlet, with local labor, panel condition, and permit fees moving the total. Never connect a generator to house wiring without one of these two devices.
Why the device is not optional
A generator that feeds your wiring with the utility connection still live can send power back out onto the utility line. That backfeed can hurt or kill line workers repairing the outage, and it can damage the generator. A transfer switch or an interlock makes it impossible for the two sources to be connected at once. NEC 702.5 is the rule that asks for this kind of transfer equipment on optional standby systems.
Because the work involves your panel, plan on a licensed electrician and an electrical permit. Your local inspector decides what they accept, so ask your town which products and which panel setups they allow before you buy anything.
The three options
| Option | Which circuits run | How you switch | Typical installed cost |
|---|---|---|---|
| Manual transfer switch (6 to 10 circuits) | The circuits an electrician moves into the switch | Flip each circuit from utility to generator | $400 to $1,300, up to $2,500 |
| Breaker interlock plus inlet | Any breaker in your panel, one by one | A plate lets the generator breaker on only while the main is off | $400 to $850 |
| Automatic transfer switch | Selected circuits or the whole house | Nothing, the switch moves itself | Sold with a standby generator |
Costs are 2025 to 2026 ranges. HomeGuide gives $400 to $2,500 total for a transfer switch and $400 to $850 installed for an interlock, and a 2026 manual-switch guide that cites Angi gives $400 to $1,300 for a standard manual switch. The kit alone is smaller: a 10-circuit 30 A Reliance Controls kit was listed at about $478 at a big-box store in June 2026, and interlock hardware often runs $40 to $80 before the breaker, inlet, labor, and permit.
Manual transfer switch
A manual transfer switch is a small separate panel next to your main panel. Your electrician moves the circuits you picked, such as the refrigerator, furnace blower, sump pump, and some lights, onto that switch. Each one has its own lever, so you turn on only what the generator can carry. Reliance Controls sells them in 6 and 10 circuit versions, and Generac’s HomeLink line runs from 8 to 16 circuits. The limit is that you are locked into the circuits that were moved. A pre-wired kit also tends to cost more to buy and install than an interlock.
Breaker interlock plus inlet box
An interlock is a metal plate fitted to your existing panel. It physically stops the main breaker and a dedicated generator breaker from being on together. You still need a generator inlet box on the outside wall and a matching double-pole breaker, which the electrician installs. The big plus is flexibility: you can run any circuit in the panel, one at a time, as long as the total stays under your generator’s rating. The catch is that you have to manage the load yourself, and the kit must be made for your panel. Westinghouse’s WLock G, for example, is built for GE 150 A and 200 A panels with 1-1/4 in. breaker spacing, and other panels need a kit made for that panel. Your electrician checks the panel model first.
Automatic transfer switch
An automatic switch belongs with a permanently installed standby generator. It senses the outage, starts the generator, and moves your loads for you within seconds: Generac’s controller waits about 5 seconds to confirm the outage and lets the engine warm up about 5 seconds before it takes the load. You normally buy it with the unit rather than on its own. Generac and Kohler sell their standby generators with or without the switch, and its cost sits inside the total for a whole-house system. If you only own a portable, you choose between the first two options.
Inlet and cord ratings
Whichever device you pick, the generator plugs into an inlet box on the outside of the house. The inlet’s rating has to match the cord and the generator’s outlet.
| Inlet | Common plug | Amps | Watts at 240 V |
|---|---|---|---|
| 30 A | L14-30 | 30 | 7,200 (rated 7,500 at 250 V) |
| 50 A | varies by maker | 50 | 12,000 (rated 12,500 at 250 V) |
Maker labels use 250 V, which is how Reliance’s PB30 inlet box shows up as a 7,500 W part. At the 240 V your house runs on, 30 A is 7,200 W and 50 A is 12,000 W. You can check any figure with the watts to amps calculator. Many mid-size portables put out 7,500 W or less and have an L14-30 outlet, so a 30 A inlet is the common match. A generator rated above 7,500 running watts outgrows the 30 A inlet and needs the 50 A inlet and its heavier cord. The generator’s own running watts are the real limit, not the inlet.
The licensed electrician installs a double-pole breaker that matches the inlet’s amps and wire sized for it. If you are comparing quotes, pick the 30 A or 50 A breaker in the wire size calculator to see why the 50 A inlet needs heavier wire.
Pick the generator size before the switch
Size comes first because the switch only decides which loads you can reach. The generator decides how many of them run at once. Add up the running watts of what you want, then add the single highest starting watts, and the generator size calculator does that for you. A 10-circuit switch with a 3,500 W generator will have circuits you cannot turn on together.
To choose which circuits to back up, start with what spoils or hurts when it stops: the refrigerator and freezer, the furnace blower, a sump pump, a well pump if you have one, and a few lights. Add comfort loads like a microwave or a window air conditioner only if your total still fits. The big electric loads, such as an electric range, dryer, water heater, and central air conditioning, are the ones that usually do not fit on a portable.
Where the generator goes
Run a portable generator outdoors only. Ready.gov says to keep it at least 20 feet from windows, doors and attached garages, and the CPSC says at least 20 feet from the house. Generators put out carbon monoxide, which has no color or smell, so aim the exhaust away from the house. Keep the unit dry, since a wet generator can shock you. Install carbon monoxide alarms with battery backup on every level of your home, and let the generator cool before you refuel it.
The distance affects your plan: with the generator at least 20 feet out, the cord has to reach the inlet, and a short cord that comes in a kit may not. Longer cords with the same plug and amp rating as the inlet are sold separately. Ask your electrician where the inlet should go so the cord does not cross a walkway or a window.
What the electrician does and what you do
The electrician mounts the switch or interlock, installs the inlet and the dedicated breaker, runs the circuit, labels everything, tests that the utility and the generator can never both feed the house, and takes care of the permit and inspection. You do not wire any of it yourself. This guide does not give wiring steps on purpose, because a mistake can energize utility lines or start a fire.
During an outage, follow the switch or interlock maker’s operating steps, and ask your electrician to walk you through them before you need them. Run only the circuits you planned, and turn big loads on one at a time so the starting surge does not stall the unit. When utility power returns, use the maker’s steps for going back to utility power before you shut down and unplug the generator.
Getting quotes
Ask each electrician for a written price that names the device, the inlet amps, the breaker, the permit, and the cord. Treat the ranges here as a starting point, since region and panel access move the total.