Quick answer
A critical loads panel is a separate subpanel that holds only the circuits a home wants to keep running in an outage, so a battery or generator can power those must-run circuits without trying to carry the whole house.
An electrician moves chosen circuits, such as the refrigerator, lights, internet and furnace fan, from the main panel to this subpanel. The backup source then feeds just that panel through a gateway or transfer switch.
Quick facts
The key facts about Critical Loads Panel, with sources:
- Also called
- Backup loads panel, essential loads panel, protected loads panel
- Used with
- Home batteries (partial-home backup) and smaller generators 1
- Food clock without power
- About 4 hours for a closed fridge; about 48 hours for a full freezer 2
- Switching device
- Battery gateway or a transfer switch that keeps sources apart 4
Key takeaways
- A critical loads panel is a subpanel for the circuits you cannot do without in an outage.
- It lets a modest battery or generator cover the must-run circuits instead of failing under the whole house.
- Picking the circuits is the owner’s main job; wiring the panel is the electrician’s.
- Large loads like central air, ranges and EV chargers usually stay off it.
- Some newer systems use smart load control instead of a separate panel.
What a critical loads panel is
Your main electrical panel holds every circuit in the house. A critical loads panel is a second, smaller subpanel that holds only a chosen few. During normal times it gets power from the grid like everything else. During an outage it gets power from the backup source while the rest of the house stays dark.
Battery makers describe this as partial-home backup. Enphase, for example, says partial home backup suits owners who want to power the appliances they need most during an outage, with the system sized for the appliances they named as must-run with their installer 1.
The same idea works with a generator. A pre-wired circuit transfer switch is, in effect, a small critical loads panel.
The reason is simple arithmetic. A whole house can draw far more power at once than a typical home battery or small generator can supply.
Running an electric range, a dryer and central air together would trip or drain the backup in short order.
Moving only the must-run circuits to their own panel puts a hard ceiling on what the backup source ever sees, so it lasts longer and does not overload.
How power reaches the critical loads panel
- Utility → meter → main panel → lower-priority circuits
- Main panel → gateway or transfer switch → critical loads panel → must-run circuits
- Outage: gateway opens the grid side → battery or generator → critical loads panel only
- Grid returns: gateway reconnects → battery recharges → everything back to normal
- List must-run loadsWhat must run in an outage
- Add up the loadRunning watts plus motor starts
- Check the sourceBattery kW/kWh or generator watts
- Move circuitsElectrician relocates chosen breakers
- TestSimulated outage, then inspection
Types of backup layouts
| Layout | What is backed up | Notes |
|---|---|---|
| Critical loads subpanel | Only circuits moved into the new panel | Classic partial-home backup 1 |
| Whole-home backup | The entire main panel | Needs a larger battery bank or generator 1 |
| Whole-home with load control | Whole panel, but big loads are shed when needed | Avoids moving circuits |
| Pre-wired circuit transfer switch | A handful of circuits for a generator | Generator equivalent of a critical loads panel |
Example: a typical must-run list
A sample sort shows how an owner and electrician might sort circuits. Exact loads come from your nameplates. The food-safety times are from Ready.gov 2.
| Circuit | On critical panel? | Reason |
|---|---|---|
| Refrigerator and freezer | Yes | Fridge food stays cold about 4 hours, a full freezer about 48 hours 2 |
| Internet modem and router | Yes | Communication; small load |
| Furnace blower or boiler controls | Yes | Heat in winter; small motor |
| A few lighting circuits | Yes | Safe movement |
| Well pump or sump pump | Yes, if present | Water and flood protection; check the motor start |
| Central AC, range, dryer | Usually no | Large loads that would drain or overload the source |
| EV charger | No | 2023 NEC counts it at 7,200 VA or more 3 |
Use the appliance circuit lookup to see typical circuit sizes for each appliance.
Where it shows up
Physically, the critical loads panel usually mounts beside the main panel, often next to the battery gateway. On a quote it appears as “backup loads panel,” “critical loads subpanel” or “essential loads relocation.”
On permit drawings it is shown as a subpanel fed from the gateway, with a list of the circuits moved. Ask for that list in writing so you know what will work during an outage.
Benefits and drawbacks
What it does well
- A smaller battery or generator can cover what matters.
- Longer runtime because large loads are kept off.
- Clear, labeled set of backed-up circuits.
- Works with batteries and generators alike.
Where it falls short
- Circuits must be chosen up front; changing later means more electrician work.
- Needs wall space and may require panel changes.
- A circuit that feeds several rooms brings all of them along.
- Expanding to whole-home backup later may need reconfiguring.
Where a critical loads panel gets tricky
- Shared circuits. Many older homes have one circuit spread across rooms, so “just the fridge” may bring along other outlets.
- 240-volt loads. A well pump or heat pump can exceed a battery’s kW rating at start-up.
- Panel space. The main panel needs room for the feed; check with the panel space tool.
- Service type. Check the battery’s spec sheet for supported service voltages before the panel is planned.
What drives the cost
No dollar figures here. These factors move the quote; the cost tool shows the electrical pieces.
- Number of circuits moved. Each relocation is labor.
- Distance between panels. Longer runs need more wire.
- Main panel condition. A crowded or old panel may need work.
- Gateway or switch type. Set by the battery or generator maker.
- Permit and inspection. Set by your town.
- Warranty. Panel hardware is usually long-lived; backup equipment carries its own warranty.
How installation works
A licensed electrician or storage installer does this work.
- Walk through the house and agree on the must-run list.
- Measure or estimate those loads, including motor starts.
- Confirm the battery or generator can carry them.
- Pull a permit; install the subpanel and gateway or switch; move the circuits.
- Label both panels, run a simulated outage and pass inspection.
Upkeep
- Keep the circuit list on the panel door current.
- Test with a simulated outage once a year, with the installer if the system has no self-test.
- Avoid plugging new heavy loads into backed-up outlets.
- Keep the panel area clear and dry, with the working space in front of it free of storage.
- After any remodel, check that new circuits did not end up on the backup panel by accident.
Warning signs
If the backup source trips during outages, the panel likely holds more load than it can carry. If backed-up outlets lose power while others work, there may be a wiring or gateway fault. Either way, call the installer.
Warm panel covers, buzzing, or a burning smell need an electrician right away; see emergency electrician help.
Two sources means two ways to be live
A critical loads panel can be energized by the battery or generator even when the grid is down and the main breaker is off. Never open it or work on its circuits. Only a licensed electrician should service it.
Codes that apply
| Authority | Rule | What it covers |
|---|---|---|
| NFPA 70 (NEC) | 2017 ed. as cited by UL, Section 702.5 | Transfer equipment must prevent accidental interconnection 4 |
| NFPA 70 (NEC) | 2023 ed., Section 220.57 | EVSE load at 7,200 VA or nameplate, whichever is larger 3 |
| ICC | 2021 IRC Section R328 | Placement and size limits for the battery feeding the panel 5 |
| Local inspector | Adopted code edition | Approves the subpanel, feed and labeling |
Critical loads panel vs related terms
| Term | What it is | How it relates |
|---|---|---|
| Subpanels in general | Any panel fed from the main | A critical loads panel is one kind |
| Transfer switch | Device that picks the source | Feeds the critical panel from a generator |
| ATS | Self-acting transfer switch | Can feed a partial-home panel |
| Load calculation | Sum of expected loads | Decides what fits on the panel |
Myths
- Myth I can pick individual outlets.
- Reality You pick circuits, and one circuit may serve several outlets and rooms.
- Myth More circuits on the panel is always better.
- Reality Every added load shortens runtime or risks overload.
- Myth A critical loads panel is required for any battery.
- Reality Whole-home designs exist; partial-home is one option 1.
State factors
Which NEC and residential code editions your state has adopted decide the rules for the panel and the battery feeding it. Outage exposure also differs: EIA reported nearly 53 hours without power in South Carolina in 2024, versus 11 nationally 6.
Do you need one?
If your battery or generator is smaller than your whole-home load, a critical loads panel is the simplest way to make it last. If you can afford a large battery bank or a whole-home generator, you may skip it.
Start with a list of must-run circuits and the load calculator, then ask your installer to show you which circuits fit.
Walk the house with the breaker list
Before the installer arrives, flip one breaker at a time during the day and note what goes dark. That map makes the must-run list accurate.
Questions about Critical Loads Panel
What is a critical loads panel?
On the wall it looks like a second, smaller breaker box beside the main panel, usually with a handful of breakers and a label such as “backup loads.”
Those breakers are the circuits an electrician moved over from the main panel, and they are the only ones the battery or generator feeds when the grid is down.
What should go in a critical loads panel?
Most homes choose the refrigerator and freezer, internet equipment, a few lighting circuits, furnace or boiler controls, and a sump or well pump if present. Large loads like central air, electric ranges, dryers and EV chargers usually stay off, because they would drain or overload the backup source quickly.
Do I need a critical loads panel for a home battery?
Not always. Partial-home backup with a critical loads panel suits smaller systems. Whole-home backup, where the gateway switches the entire main panel, is an option with enough battery capacity. Some systems use load control to shed big loads instead. Your installer sizes the system to the layout you choose.
Can I move circuits into the critical loads panel myself?
No. Moving circuits means working inside live panels and changing how a second power source connects, which is licensed electrician work with a permit. Your part is choosing which circuits matter and mapping what each breaker controls with the power on, so the electrician knows what to move.
How many circuits can go in a critical loads panel?
The limit is the backup source, not the panel. The total running load and the largest motor start must fit within the battery’s kW rating or the generator’s watts, and the stored kWh or fuel decides runtime. A load calculation shows how many circuits fit.
Is a critical loads panel the same as a subpanel?
It is a type of subpanel. Any panel fed from the main is a subpanel. A critical loads panel is one set aside for circuits that stay powered during outages, fed through a gateway or transfer switch that can connect it to the backup source.
Will a critical loads panel work with a generator?
Yes. A pre-wired circuit transfer switch or a subpanel fed through an automatic transfer switch works the same way: only those circuits get generator power. The transfer equipment must keep utility and generator power from ever connecting, as NEC 702.5 requires.
What happens to the rest of the house in an outage?
Circuits left in the main panel go dark until the grid returns. Only the circuits in the critical loads panel stay on. That is why mapping your breakers ahead of time matters, so you are not surprised by which rooms have power.
Can I add circuits to the backup panel later?
Usually, if there is space in the panel and capacity in the backup source. It means another electrician visit and possibly a permit. Some owners who later add batteries switch to whole-home backup, which can require reconfiguring the system.
Sources
- Enphase, Storage System Owner’s Guide (partial and whole home backup), retrieved .
- Ready.gov, Power Outages, retrieved .
- Larimer County (CO), 2023 NEC Significant Code Changes, retrieved .
- IAEI Magazine, UL Question Corner: NEC 702.5 transfer equipment, 2017 NEC, May/June 2017, retrieved .
- UL Code Authorities, 2021 Residential ESS Requirements (IRC R328), retrieved .
- U.S. EIA, Today in Energy: hurricanes in 2024 led to the most hours without power in 10 years, retrieved .
Expert review
Written by the HyreElectrical Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Checked against Enphase’s owner’s guide, Ready.gov, Larimer County’s 2023 NEC summary, IAEI’s UL column, UL’s IRC R328 summary and EIA outage data on 2026-10-10.
Suggest a correction. We fix errors and say what changed.