How the panel and transfer switch work
The generator is only half of backup power. The other half is inside: the main panel, the transfer switch, and which circuits the generator actually reaches. Cut the power, compare the two common hookups, and see why a generator must never be plugged into an outlet.
Right now
- Utility power
- On
- Main breaker
- On
- Transfer switch
- On utility
- Generator
- Ready
- Circuits with power
- 6 of 6 switched on
- Voltage
- Steady
What just happened
Cut the power to start. Click any circuit to switch it on or off.
Essentials only, or the whole house.
Either way, the transfer switch connects its circuits to the utility or the generator and never both. The difference is how many circuits sit behind it.
| Critical-load subpanel | Whole-house switch | |
|---|---|---|
| What runs in an outage | Only the circuits moved into the subpanel: well pump, heat, fridge, some lights and outlets | Everything in the house, with a load manager switching off the biggest loads |
| Generator size | Smaller, because it only carries the essentials | Larger, sized for the whole house or paired with load management |
| Where the switch sits | After the main panel, feeding a small subpanel | Between the meter and the main panel, as the house's service disconnect |
| The catch | Anything left in the main panel is dark, and people find out in the first storm | Without load management, big appliances can overload the generator |
Myths about plugging a generator into the house.
Every storm season, someone plugs a portable generator into a dryer outlet with a double-ended cord to power the house. It powers the house, and it also sends power wherever the wiring lets it, including back out to the street.
Myth
If I turn the main breaker off first, a generator in the dryer outlet is safe.
Reality
The main keeps the power off the street only while it stays off, and nothing stops someone switching it back on. The cord's other end has live bare prongs, and the setup breaks the electrical code.
Myth
My generator is too small to hurt anyone on the line.
Reality
The transformer on the pole works in both directions. It steps 240 volts up to the thousands of volts on the line, whatever size the generator is.
Myth
The line crew will know my generator is running.
Reality
Crews treat downed lines as live and take precautions, and backfeed is one of the hazards those precautions exist for. They shouldn't have to count on it.
Myth
An interlock is just a fancier way of doing the same thing.
Reality
An interlock is a plate that makes it physically impossible to have the main and the generator breaker on at the same time, with a proper inlet instead of a cord with bare prongs. It's installed by an electrician, with a permit.
The safe ways to use a portable generator are a manual transfer switch or a panel interlock with an inlet box, installed by a licensed electrician with a permit, or extension cords run from the generator directly to the appliances. Run it outside, away from windows and doors.
Six calls that start with "the power's out."
The first question sorts most of them: do the neighbors have power? Pick one to see it play out on the drawing.
Overloaded generator
"The generator comes on, then everything cuts out again after a few seconds."
On a whole-house switch every circuit can reach the generator, so the heat pump, the dryer and the EV charger can all ask for power at once. The generator's breaker trips and the house goes dark. A load manager fixes it by switching the biggest loads off while the house is on generator power.
Transfer switch stuck
"I can hear the generator running, but the house is dark."
The generator starts and runs, but the transfer switch never moves, so no power reaches the house. A failed control board, a blown fuse or a damaged control wire between the generator and the switch are the usual causes.
Main breaker tripped
"Half the house is out, but the neighbors have power and the generator is running."
The street has power but the house doesn't, because the main breaker tripped. In a critical-load setup the transfer switch is fed through the main panel, so it sees no power and starts the generator, and only the subpanel's circuits come back on.
Well pump not on the subpanel
"The generator works, but we have no water when the power's out."
With a critical-load subpanel, only the circuits that were moved into it get generator power. If the well pump was left in the main panel, the house has lights and heat in an outage but no water, and the owner usually finds out during the first storm.
Lost neutral
"Some lights are really bright and others are dim, and they change when the fridge kicks on."
The neutral wire from the utility balances the two halves of the panel. When it breaks or corrodes, often at the service drop after a storm, the voltage swings: some lights glow too bright while others dim, and electronics can be damaged. It's a utility or electrician emergency.
Generator in the dryer outlet
"Can I just plug my generator into the dryer outlet if I turn the main off?"
A portable generator plugged into a dryer outlet with a double-ended cord sends power backward through the panel. If the main breaker is on, it goes out through the meter to the transformer, which steps it up to thousands of volts on the lines a crew is repairing. Even with the main off, the cord's plug has live bare prongs, nothing stops the main from being switched back on, and it breaks the electrical code. The safe ways to connect a portable generator are a transfer switch or a panel interlock installed by an electrician.
Where AI helps the office and the trucks.
Storms bring a wave of calls that sound the same and aren't, and generator season brings quotes that each need a load calculation and a pile of paperwork. Both are work software can take a first pass at, with an electrician making the calls.
Storm calls sorted by the first question
Do the neighbors have power? A tripped main, a lost neutral and a real outage sound alike on the phone. An intake agent asks the questions on this page, tells a caller with swinging lights to turn off the main and call the utility, and puts the rest in the right queue.
Custom AI agentsGenerator proposals from a panel photo
The homeowner sends a photo of the panel directory and a list of what they need in an outage. AI drafts the critical circuit list and the generator size for the electrician to check, before anyone drives out.
Custom AI agentsPermits and inspections tracked
Every generator install needs a permit, a utility notice and an inspection. AI keeps each job's paperwork moving and reminds the office what's waiting on whom.
AI Cowork training
This page is a simplified picture for learning, not a wiring guide. Don't open an electrical panel's cover: work inside it is for a licensed electrician, and a generator hookup needs a permit and an inspection. If lights swing bright and dim, turn off the main breaker and call the utility. Stay away from downed lines and treat them as live.
