Generator inlet box (power inlet) installation

What the inlet box is for

Without an inlet, people run a heavy extension cord through a cracked window to power a few things. That leaves a gap for rain and pests, and the cord only runs what it plugs into. An inlet box fixes the awkward part. It is a small outdoor box with a locking, weatherproof receptacle on the side of the house. A cable inside the wall runs from it to your panel. You plug the generator in outside, and the house is powered through the panel.

The inlet does not make anything safe on its own. It only supplies a plug. The safety comes from the device on the other end of the cable: a generator interlock kit or a transfer switch. If the inlet is connected to the panel without one of those, power can flow back onto the utility lines, which is the main hazard utilities warn about with generators.

Choosing the rating

Inlets come in common ratings of 30 amps and 50 amps. The rating needs to match the generator output and the circuit wire. Bigger is not always better: a 50 amp inlet on a small generator just means more expensive wire.

Inlet	Typical use
30 amp	Mid-size portable generators for a fridge, lights, furnace fan, internet
50 amp	Large portable generators that can support more circuits at once

Pick the generator and the inlet together. If you already own a generator, bring its model number. The outlet type on the generator decides the plug style.

Placement matters

• Keep it outdoors. The generator needs to run outside, away from windows, doors and vents. Exhaust carries carbon monoxide.
• Keep the run short. Every extra foot of cable adds cost, and some walls are hard to cut into.
• Keep it dry. Choose a spot under an eave if possible. A cover on the inlet helps in rain.
• Keep it secure. The generator cord should not cross a walkway.
• Check clearances. Inspectors look for working space, gas meter distances and labels. Cities set the details.

Stucco and block walls need core drilling, which adds labor. Often a better route runs through the garage.

Costs as of October 2026

A published cost guide puts an interlock install at $400 to $850. Adding an inlet box and a cord raises the total to as much as $1,800. The same guide covers transfer switches at $400 to $2,500. The cost page has the full range for the interlock-and-inlet combination.

What moves it within that range:

• Distance from the panel to the inlet
• Wall type and finish
• Wire and conduit size for 30 amps or 50 amps
• Whether the generator cord is included
• Whether a permit and inspection is bundled

Permit and inspection

An inlet box is part of a change to the home’s service equipment. Cities normally want an electrical permit and an inspection, and the inspector looks at the inlet, the labels and the lockout device. Permit rules differ by city. See electrical permits in Southern California.

Checklist for the visit

1. Photograph the panel with the door open.
2. Say where the generator will sit.
3. Have the generator model on hand.
4. List the circuits you most need on.
5. Ask whether the cord, labels and permit are in the price.

If you are leaning toward a battery instead, the inlet may still be worth installing as a second source. See generator vs battery backup.

Labels and warnings

The inlet, the panel and the meter area should carry labels that show the generator source and warn anyone working on the equipment. Inspectors look for them. The labels matter during a real outage too, because a house guest or a neighbor helping at night should see right away that the house is also fed from the generator.

Keep the generator cord stored where you can find it in the dark, with a note on how to connect it. Many people tape a laminated card to the panel door with the steps from the electrician.

Maintenance

Run the generator under load a few times a year and keep fuel fresh, since old gasoline gums up carburetors. Check the inlet cover for cracks and the pins for corrosion. A plug that has overheated shows discolored plastic and should be replaced.