Every hurricane season, the same scene plays out in Prairieville. The storm rolls through, the power goes out, and by the second afternoon there are generators running on front porches with orange extension cords snaked through a cracked window. I understand why. It is 95 degrees, the house is hot, and the fridge is starting to smell.
What I want to talk about is the next thing people try, which is running the house off that generator properly. That is where it gets dangerous, and there are two very different ways to do it.
Why backfeeding is the part that kills people
Plug a generator into a dryer outlet, or wire it into your panel without a mechanical disconnect, and the generator pushes power back up the service line. It does not stop at your meter. It goes out to the transformer on the pole, gets stepped up to thousands of volts, and now it is sitting on the line the crews are working on three streets over.
NEC Article 702 is the section that covers this. What it asks for, in plain terms, is a mechanical barrier. Your panel can draw from the utility or from the generator, never both at once.
That is the entire reason the two options below exist.
Option one: an interlock kit
An interlock is a metal plate that bolts onto the dead front of your existing panel. It physically blocks the generator breaker from being switched on while the main is on. Shut the main off, the plate slides, and now the generator breaker can move. There is no way to have both live at once, because the metal will not let you.
The advantage is access to the whole panel. Once the interlock is in, every circuit in the house can draw from the generator. You cannot run everything at once, since a 7,200-watt portable will not carry your AC and your water heater and your dryer together, but you get to choose. Run the fridge, the well pump, the living room and a window unit, and leave the rest off. Want hot water for an hour? Kill the non-essentials, turn the water heater breaker on, then turn it back off.
For most Prairieville homes with a modern panel and two open slots near the main, this is the practical answer. It costs less than a transfer switch and gives up almost nothing.
Option two: a transfer switch
A transfer switch isolates specific circuits. Instead of the whole panel, you get a small subpanel with six to ten circuits moved into it. The fridge, the freezer, the internet and a couple of lighting runs live on those circuits permanently.
The upside is that it is dead simple to use. Flip the switch, start the generator, done. The downside shows up on day four of an outage, when the one circuit you did not move over is the one you need, and it cannot be energized without opening the panel again.
With a permanent standby generator, you get an automatic transfer switch instead. It watches the incoming voltage, starts the engine when the grid drops, transfers the house over, and transfers back when the power returns. That is a different project with a different budget, and it is worth its own conversation.
What it takes to install one
The generator does not connect to the panel directly. It plugs into an inlet box outside the house, and the inlet is hardwired to a breaker in the panel.
- 30-amp inlet (NEMA L14-30P). Good for portables up to about 7,200 running watts. 10 AWG copper, 30-amp two-pole breaker.
- 50-amp inlet (NEMA 14-50 or CS6365). For the larger portables, up to about 12,000 running watts. 6 AWG copper, 50-amp two-pole breaker.
Either way, the inlet goes on an exterior wall away from windows and doors, and the run to the panel is usually rigid conduit. We put it where the generator can sit out in the open, not under a carport where the exhaust collects.
You also need two open breaker slots at the top or bottom of the bus, next to the main. That is the part people find out late. If your panel is packed with tandem breakers, or the bus has been hot, the honest answer is that the panel gets replaced first. Same story if it is one of the older models insurers no longer want to see.
One thing to know before you buy anything: this work is permitted and inspected. In East Baton Rouge that comes through the Permit and Inspection Division, Department of Development, on North 10th Street. In Ascension Parish it goes through the parish permit office. The inspector is checking the same thing the code is checking, which is that the interlock physically prevents backfeeding.
A note from the truck
If your panel has the space and the bus is sound, an interlock gives you the most capability for the least money. If it does not, I would rather tell you that up front than sell you a kit that fails inspection.
Straight answers to the questions I get asked
Can I run my central AC on a portable generator with an interlock? Usually not without help. A 4-ton condenser draws somewhere around 16 to 20 amps while running, but the startup spike, called locked rotor amps, is typically 90 to 115 amps for less than a second. That will stall most portables. A soft starter on the condenser cuts the inrush sharply, with manufacturers claiming 60 to 70 percent. With one installed, a 9,000-watt-and-up portable can carry the AC.
Do I need a permit? Yes. Adding an inlet and a backfeed breaker is permitted, inspected work in every parish around here.
Why can't I just use a double-male cord into the dryer outlet? Because that cord has live prongs on one end. It bypasses every overcurrent device between the generator and your house and it backfeeds the neighborhood, which is the exact scenario the lineman up the street does not survive. Insurance companies treat it the way you would expect.