Portable generator inlet box, done right

A portable generator in the driveway does nothing useful for the house until the power gets inside without traveling back out to the street. The inlet box is the weatherproof plug on the exterior wall. You run a cord from the generator to that inlet, then an interlock or a transfer switch inside decides that the house is on the generator and not on the utility. That combination is the legal hookup. A cord in a dryer outlet is how people energize lines that a lineman thinks are dead.

This page is the portable-generator version of the hardware. If you are buying a pad-mounted standby, you want the automatic vs manual transfer switch guide instead. If you have not picked a machine, start with battery vs generator.

What does the hookup cost?

HomeGuide’s 2026 transfer-switch cost guide breaks the portable pieces out:

• Power inlet box: $20 to $100
• Heavy-duty power cord: $30 to $350
• Interlock kit installed (kit, inlet, breaker, labor in their job-supplies band): $400 to $850
• Manual transfer switch installed: $400 to $1,300
• Labor for a straightforward switch job: $200 to $500, often 2 to 4 hours
• Kits that bundle switch, inlet, and cord: about $300 to $500 for the hardware

HomeGuide: generator transfer switch installation cost

Cost to Renovate’s 2026 transfer-switch page puts the exterior inlet at $50 to $150 and the heavy-gauge run from the panel to the outside at $100 to $350, inside a typical whole-job band of $700 to $2,000 (national average around $1,200). Extra run length is real money on that page: on the order of $30 to $50 per extra 10 feet.

Cost to Renovate: generator transfer switch

The generator itself is extra. HomeGuide puts portables around $500 to $2,500. Don’t compare a $650 interlock-plus-inlet bid to a $12,000 standby package. Those are different jobs.

A long run through a finished wall, a panel that will not take a listed interlock, or a 50-amp inlet far from the basement panel will sit above those averages. A 30-amp inlet next to the garage, two feet from the panel, is the bottom.

What do three real-looking bids mean?

Bid A, $400 to $850. Listed interlock for your panel brand, 30-amp inlet on the garage wall next to the panel, generator breaker, permit. You supply a matching L14-30 cord. This is HomeGuide’s interlock band. You still flip breakers in the dark, so you need the critical-load list taped inside the door.

Bid B, $800 to $1,400. Six- to ten-circuit manual transfer switch, 30-amp inlet, cord in the kit, circuits pre-chosen (fridge, furnace or heat-pump air handler, a few lights, internet). HomeGuide’s manual-switch band. You pay more so you are not doing breaker yoga at 2 a.m.

Bid C, $1,800 to $2,500+. 50-amp inlet on the far side of the house because that is the only legal place to park the generator, long feeder through finished space, maybe a small subpanel, maybe the existing panel will not take a listed interlock so the electrician is building a proper switch setup. Cost to Renovate’s upper whole-job band. If this is the quote, ask whether a standby package is actually the next conversation, because you are already in serious electrical money.

If Bid A is $500 and Bid B is $1,800, A is often an inlet with no interlock, or an interlock with no inlet. You need both.

30-amp or 50-amp?

Match the inlet to the generator’s outlet, not to a wish. Most smaller portables use a NEMA L14-30 (30-amp, 120/240-volt twist-lock). Larger open-frame units often use a 14-50 or a CS6365-style 50-amp inlet. HomeGuide’s amp table is a sanity check on the switch side: 30-amp hardware is associated with roughly 7,500 to 8,000 watts, 50-amp with 8,500 to 12,500 watts. If the generator is 30-amp and the inlet is 50-amp, you own an adapter story and a mismatched breaker.

The cord is four-wire: two hots, a neutral, and a ground. A three-wire dryer cord is the wrong object. Length matters twice. You need enough cord to park the generator outside, away from doors and windows, with exhaust pointed away from the house. HomeGuide’s transfer-switch FAQ puts most generators 60 to 70 feet from the switch as a practical maximum, and 5 to 15 feet from openings for carbon monoxide. Never run it in the garage, even with the door up.

Buy the cord that matches the inlet. Adapters that turn a 30-amp generator into a 50-amp house inlet do not add capacity. They just let you plug in and overload the smaller machine.

Interlock vs a small transfer switch

Interlock: a sliding plate on the panel so you cannot turn the generator breaker on while the main is on. You still pick which branch breakers to leave on, and you still have to be home, so it is cheap and still manual. It needs a listed kit that matches the panel brand, a generator breaker, the inlet, and a permit. HomeGuide’s installed band is $400 to $850.

Manual transfer switch: a separate small panel or a six- to ten-circuit switch. You flip one handle (or a row of switches) instead of doing breaker yoga. Circuits are pre-chosen. HomeGuide’s installed band is $400 to $1,300. A six-circuit unit is enough for fridge, furnace, a few lights, and internet if you did the critical-load list first.

Either one is a complete portable hookup if the inlet, cord, and permit are in the price. Neither starts the generator for you. You have to be home.

An interlock that is a homemade bar, a piece of wood, or a zip tie is not a listed kit. Inspectors fail those, and they fail for a reason: nothing mechanical is stopping you from feeding the street.

Where should the inlet live?

On the outside wall, in the weather, as close to the panel as you can without putting the generator under a bedroom window or next to the dryer vent. Closer to the panel means less heavy wire. The inlet should be high enough that snow doesn’t bury it and far enough from the meter that the inspector doesn’t hate the working space.

Ask the electrician to stand where the generator will sit during an ice storm, then point at the inlet. If that story requires a 40-foot cord across the walk, pick another wall. You will not want to drag a wet 6-gauge cord around the house at midnight.

Keep a working carbon monoxide alarm on every floor, and do not “just this once” pull the generator into the garage because of rain. The inlet exists so the machine can stay outside.

What should be on the quote?

1. Inlet type and amps (L14-30 vs 14-50 vs CS6365), location, and who supplies the cord.
2. Interlock (listed kit, panel brand) or manual transfer switch (circuit count and which circuits).
3. Generator breaker size, wire size, and that it is four-wire.
4. Permit and inspection.
5. What you must turn off so you don’t overload the portable (the load list).
6. What is excluded: the generator, a cover, a new panel.
7. A test: after inspection, run the generator, transfer, and confirm the labeled circuits actually come on.

If the bid says “generator outlet” and does not say inlet plus interlock or transfer switch, it is a dryer receptacle with extra steps.

What goes wrong after you sign?

The inlet is 50-amp and the generator is 30-amp. The interlock is a homemade bar, not a listed kit, and it fails inspection. The cord is a dryer cord. The inlet is on the front porch ten feet from the bedroom window. Nobody labeled the breakers, so in the dark you leave the well and the range on and the generator dies. Someone stored the generator in the garage “just for tonight.” The first storm is also the first test, and the inlet was never energized under load.

Never backfeed. Inlet, interlock or transfer switch, permit, generator outside.

If you later size a standby, the portable inlet is not wasted knowledge. The sizing guide is the next question once a portable cannot cover the well plus the heat.

How do I decide in one afternoon?

1. Read the outlet on the generator you own or plan to buy. That is the inlet amperage.
2. Decide whether you can flip breakers (interlock) or want a short labeled list (manual switch).
3. Get a bid that names inlet, cord, interlock or switch, and permit as separate lines.
4. Walk the yard and mark where the generator will sit, then put the inlet on that wall.

The inlet is a small box. The rest of the job is what keeps it from being a dangerous one.