How Much Load Does AC Put on an Electrical Panel in Phoenix?

The AC load on an electrical panel is the question behind a lot of the calls we get in Phoenix. Can a 200 amp panel run two AC units? Will a bigger system overload it? Do I need a service upgrade for a heat pump? The honest answer depends on your house, but the way to find it is the same every time, and you can follow most of it yourself before you call anyone.

Reading your AC's electrical numbers

Every outdoor condenser has a data label, usually on the side panel. Two numbers matter for your electrical system:

• MCA (minimum circuit ampacity): the smallest wire size the circuit can use, expressed in amps. This is the closest thing to the unit's real running demand on paper.
• MAX fuse/breaker (sometimes MOCP): the largest breaker the manufacturer allows on that circuit. It's set above the running current so the breaker doesn't trip when the compressor starts.
• LRA (locked rotor amps): the momentary current the compressor pulls as it starts. It's much higher than the running current, but it only lasts a fraction of a second.

Indoor equipment has its own label. With a straight AC and gas furnace, the indoor blower is a small load. With a heat pump or an electric furnace, the air handler usually contains electric heat strips. In some homes those strips draw more than the condenser does, so they belong in the math too.

Why adding up breakers doesn't work

Open almost any panel and add the numbers on every breaker, and the total will be well past the main breaker. That's normal. Breakers protect wiring, and most circuits never run near their rating, and never all at once. A panel isn't "full" because the breakers add up to more than 200.

The reverse is also true, and it matters more in Phoenix. An AC compressor can run close to its rating for hours, every afternoon from May into October. That's why the code treats air conditioning differently from a bedroom outlet circuit, and why a house can feel fine in March and trip the main in July.

How a load calculation actually works

A load calculation is the method electricians and plan reviewers use to decide what size service a home needs. In plain terms it goes like this:

• General loads are figured from the home's square footage, plus kitchen and laundry circuits, and then reduced, because not everything runs at once.
• Fixed appliances like the range, dryer, water heater and pool equipment are added from their nameplates, with reductions allowed in some cases.
• Heating and cooling go in at full value. Since you don't run the AC and the heat at the same time, the calculation counts whichever one is larger, not both.
• EV chargers and other new loads go in at their full rating unless a load management system limits them.

The total, divided by the voltage, gives the amps the service needs. For scale: a 200 amp service at 240 volts works out to 48,000 volt-amps of capacity. Your AC takes the biggest single bite of that, and everything else has to fit in what's left. We go deeper on the next step up in our 200 amp vs 400 amp service guide.

Is 200 amps enough for two AC units?

Often, yes. Plenty of Phoenix homes run two AC units on a 200 amp service without trouble. Where it gets tight is when the two units come with everything else Phoenix homes tend to add over time: a pool and heater, an electric range, an EV charger, a casita with its own mini split. Each one is reasonable on its own. Stacked together, they can push the calculation past what the service can carry.

Older homes are the other case. A 100 or 125 amp panel that was sized for a swamp cooler and a gas range was never meant to carry modern central air plus a second unit. That's not a breaker swap. It's a service upgrade, with a permit, utility coordination with SRP or APS, and a city inspection. Our SRP vs APS guide explains the utility side.

Heat pumps, replacements and second units

• Switching from gas heat to a heat pump: the cooling side may be similar to your old AC, but the backup heat strips are a new electric load. Check the air handler's nameplate before you assume the panel is fine.
• Replacing an old unit with a bigger one: a larger unit can need a larger breaker and wire. The existing circuit has to match the new nameplate, not the old one.
• Adding a second unit or a mini split: you need a new 240 volt circuit, a disconnect at the unit and room in the panel, and the load calculation has to pass with it included.
• Variable-speed or inverter units: many start softly instead of with a hard jolt. That helps with flicker on startup, but they still count in the load calculation at their nameplate rating.

Summer heat and the panel itself

A breaker trips on heat. A panel on a west-facing wall in a 115 degree afternoon is already hot before the AC kicks on, and the AC runs hardest at exactly that time. A loose lug or a tired breaker heats up under that load, then cools overnight, every day of the summer. That's how a marginal connection turns into a burned one. We covered the wider picture in what 115 degree summers do to your wiring. If your lights dip when the compressor starts, read why lights dim when the AC turns on to see when that's normal and when it isn't.

Two-AC ranch homes in Arcadia

We're based in Arcadia, where much of the housing is 1940s and 50s ranch homes that have been added onto for decades. A common pattern is an original small service that once ran a swamp cooler and now feeds central air, a second unit for an addition, a pool and sometimes a casita. Those are the homes where the AC load question most often ends in a service upgrade. The same goes for older parts of central Phoenix, Tempe and Scottsdale.

Want to know where your panel stands?

Send us a photo of your main breaker and your condenser's nameplate, and tell us what you're planning to add. We'll tell you whether it needs a load calculation or a bigger service, and give you a free written estimate if it does. See our panel upgrade services, or the panel upgrade cost guide for what drives the price. B and D Electric LLC is licensed and bonded, Arizona ROC 361086, and our two owners have more than 40 years of combined experience. Call or text (480) 828-1181, or request an estimate.