backup
What belongs on a critical-load panel
Walk the last outage, name the circuits you actually missed, then ask the electrician for a small extra panel and a transfer switch that cannot backfeed the street.
Think about the last time the neighborhood went dark. You probably did not miss the dryer. You missed the fridge, the furnace kicking on, maybe the sump, and the little box on the wall so the phone still worked.
Write those things down before anyone talks about kilowatts. Ready.gov’s outage advice starts the same way: take an inventory of what in the house relies on electricity, then plan for it. A salesperson who skips that list and jumps to “whole home” is selling a bigger machine than you sat with last time.
The extra panel
A critical-load panel is a small extra breaker box for that short list. On a normal day it still runs from the grid. When the street is dead, a transfer switch feeds it from a generator or a battery, and everything else on the main panel stays dark.
The switch exists so utility power and backup are never tied together. If they are, you can push power back out to the street and kill a lineman. That is why this is electrician work in most towns, and why a dryer-outlet “trick” is a bad idea even when a neighbor swears by it.
This extra panel does not make the battery bigger. It keeps the dryer from eating it.
Walk the house before you buy slots
Go to the panel. For each breaker you care about, read the label as it actually appears, even if the label is wrong. Then walk the rooms those breakers feed and ask a simpler question: did I miss this the last time the lights were out?
Most people end up with some version of this list: refrigerator, and a separate freezer if you have one; furnace or boiler controls and the blower (often not the electric heat strips); the sump; the well, if you have one; one lighting circuit per floor you actually walk; a bathroom light or receptacle you will use; the garage door opener, if that is how you leave; and the modem, router, and the internet box on the side of the house.
Everyone forgets the internet box. Then they also cannot run the thermostat app, the sump alarm, or a phone that no longer has copper.
Leave off unless the backup machine is huge: electric range, dryer, water heater, hot tub, whole-house air conditioning. Those five are why people outgrow a small switch.
Popular Mechanics notes that most manual transfer switches cover a limited set of circuits, often six to ten. Count a 240-volt breaker (dryer, range, well) as two slots, because it takes two poles in the box.
Popular Mechanics: manual transfer switch
If your “must stay on” list is already twelve circuits plus a well, you are not shopping a 6-circuit switch. You are shopping a dedicated subpanel or a bigger automatic transfer, and the quote should say so.
Add the watts after the list, not instead of it
Once the circuit list is honest, add running watts and starting watts for the greedy ones: the well, the fridge compressor, the sump, and anything medical that cannot miss. Read the metal tag on the machine (the nameplate). Don’t use a sales chart.
Order of magnitude, so you know what “greedy” looks like. A fridge is a few hundred watts running, more at start. An LED lighting circuit is tens of watts. Modem and router are tens of watts.
Furnace control plus blower is hundreds of watts, sometimes approaching 1 kW, and that is without electric heat strips. A sump is hundreds running, with a nasty start. A well pump is the one that eats generators. Starting watts can be several times running watts, and a 240-volt well is two slots.
Add the running watts. Then look at the two biggest starts (usually well plus fridge) and whether they can stagger. A 13.5 kWh battery at 1 kW of essentials is theoretically about 13 hours before you count inverter losses. That math collapses if the heat pump or the well is on the same panel.
Ready.gov also notes that a closed refrigerator keeps food cold for about four hours, and a full freezer for about 48. That is why the fridge is on the list even when you are trying to keep the panel tiny. It is not why you should also put the range on there.
Select-circuit switch, a small extra box, or whole-house ATS
Stay with the hardware for a minute. There are three common setups, and they are not interchangeable on a quote that just says “transfer switch, $2,000.”
A select-circuit transfer switch is cheaper, limited in slots, and leaves the circuits mapped in the main box. It is a common pairing with a portable generator and an outdoor inlet.
A dedicated critical-load subpanel means the electrician moves those breakers once into the small extra box. That pairs cleanly with a battery gateway or a small standby, because the gateway has a short, known list to feed.
Whole-house automatic transfer keeps everything up until the generator starts shedding load. That is the “I don’t want to think about it” story, and it is the big invoice. It is also a different product than a 10-circuit switch, so don’t compare those two prices.
An outdoor plug plus a sliding plate on the main breaker (an interlock) is cheaper than a listed automatic transfer switch. It is also easier to get wrong, and some inspectors hate it. If that is the bid, ask whether this town will pass it, in writing, before anyone cuts a hole.
The automatic vs manual transfer switch guide is the hardware decision. You already have enough here to put tape labels on breakers this weekend.
Never backfeed a dryer outlet. Ready.gov wants generators outdoors and at least 20 feet from windows, which is the placement conversation, not a garage-with-the-door-cracked story.
Which circuits stay on?
Which circuits stay on when the street goes dark? The quote should list them the way they appear in the breaker box, including the ones that stay off.
How does the house switch from utility power to the generator or battery? That’s a hand switch, a sliding plate on the main breaker plus an outdoor plug, or an automatic switch. The quote should say which one, and how many amps it is.
Is the outdoor plug outside, and can you run the utility and the generator at the same time? You shouldn’t be able to. That’s how people put power back on the street.
Who pulls the permit, and who meets the inspector?
If the bid is a round number and a brand of generator, it isn’t done. I’d get a second bid from someone who will walk the breaker box with you.
If you have a well, a medical device, or a heat pump you were hoping to sneak onto a 10-circuit switch, say that on the first call. Those three change the machine.