Whole-home versus partial backup: what the difference means

"Whole-home" and "partial" backup describe how many of your circuits keep working when the grid drops. Whole-home means everything in the house stays on. Partial means a short list of circuits does, and the rest go dark until the grid returns.

That's the whole idea. The rest of this page is why the difference matters.

What each one means

A circuit is one run of wiring from your main electrical panel, protected by a breaker. Lights in the hall might be one circuit. The oven is usually its own.

With partial backup, a chosen set of circuits is moved so they can run from the backup source. These are often called essential or critical loads. A "load" is just anything that draws power: a fridge, a router, a lamp.

With whole-home backup, the backup source is connected so it can feed the entire panel. Nothing is left off by design, though the system can still be too small to run everything at once.

The same split exists with generators. Homes may use a transfer switch "for a few circuits or the whole home."¹

Your product's manual and your electrician will tell you what a given battery system supports.

Why size is the real limit

Whole-home sounds simple. The catch is power. Whole-home generators vary widely in size.² Every big appliance that runs at once adds to the total, so a whole-home system has to be sized for the lot.

Batteries have two limits, not one. One is how much power they can deliver at once. The other is how much energy they hold. Your manual lists both. Whole-home backup on a small battery may run the lot for a short time, or it may switch itself off under load. That's a design question, and it's one for the installer.

What partial backup usually protects

Home storage can act as a backup battery during an outage.³

Ready.gov gives a first task: "Take an inventory of the items you need that rely on electricity."⁴

That inventory is the start of a loads list. Most people find the list is shorter than they expected.

Trade-offs, plainly

None of this is a ranking. Neither is better in general. A household with a well pump, medical equipment and a full-size heat pump has very different needs from a household that wants lights, a fridge and Wi-Fi.

Who does the work

Either way, the wiring changes happen at your panel. That's licensed electrician work. Don't open the panel yourself, and don't try to move breakers around to "make a backup circuit."

Bring a written list. The questions page covers what to ask.