Will It Trip the Breaker?
Add up what you want to run on shore power or a generator — and check the number that actually trips things: starting watts, the split-second surge when a compressor kicks on.
1 · Pick your power source
Plugged into a friend's garage? A campground pedestal? Boondocking on a generator? Your budget is whatever that source can deliver — pick it here.
2 · Flip on your appliances
Check everything that would run at the same time. Watts are typical presets — tap an appliance open to match your actual labels. Air conditioners can be doubled up (front + rear), each with its own soft start.
3 · The verdict
50A fine print: your rig splits circuits across two 120V legs of 6,000 W each. The panel decides which leg each circuit lives on — worst case, assume the big loads share one leg and keep the heavy hitters under ~6,000 W. And because a big start surge hits whichever single leg that appliance lives on, the worst-case start check above is figured against one 6,000 W leg — not the full 12,000 W.
Ways to get under budget
Estimates only. These presets are typical loads — your actual nameplate ratings vary, wiring and pedestal condition matter, and hot weather raises compressor draw. Never bypass or upsize a breaker to "fix" a trip; the breaker is protecting your wiring. See our full disclaimer.
How the math works
- Running vs. starting watts. Running watts are the steady draw once an appliance is going. Anything with a compressor or motor also needs a much bigger starting (inrush) surge for a fraction of a second — that surge, not the steady load, is what stalls generators and trips marginal circuits.
- LRA — locked-rotor amps. The instant an AC compressor starts, the rotor isn't spinning yet, so it briefly draws its locked-rotor current — a 13,500 BTU rooftop unit can spike to ~4,500 W even though it runs on ~1,350 W.
- The worst-case start check adds the running load of everything else that's on, plus the single largest start surge among your appliances, and compares it to what your source can deliver at that instant.
- Breakers ride through a brief surge; generators don't. A thermal breaker takes seconds to heat up, so for shore power we allow roughly 2× the rating for the split-second start. A generator's inverter has a hard electronic ceiling — its peak watts — so that's the limit we use.
- Altitude derating. Thin air means less oxygen per intake stroke, so engine generators lose roughly 3% of output per 1,000 ft above ~500 ft. A "2,200 W" generator at 5,000 ft is really a ~1,900 W generator.
- What a soft start does. A soft start ramps the compressor up instead of slamming it on, cutting the start surge from ~4,500 W to ~1,800 W on a 13.5k unit — it's how small inverter generators start rooftop ACs.
- Presets are typical values. Check the data plate or label on your actual appliances and edit the numbers — that's why every field is editable.
Gear that pairs with this calculator
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FAQ
Why does my A/C trip a generator that's "big enough" on paper?
The number that matters at the instant the compressor kicks on isn't running watts — it's starting (locked-rotor) watts, which are typically 3–4× higher. A 13,500 BTU rooftop unit that runs on about 1,350 W can spike to roughly 4,500 W for a fraction of a second while the rotor gets moving. A generator's surge rating only lasts a few seconds, and an inverter generator has a hard electronic ceiling at its peak watts. Altitude compounds it: engine generators lose roughly 3% of output per 1,000 ft above 500 ft, so a generator that looks big enough on the sticker can bog down or trip its overload the moment the compressor starts.
What does a soft start actually do?
A soft start staggers the compressor's start, ramping it up over a fraction of a second instead of slamming it across the line — which cuts the inrush surge by roughly 60–70%. On a typical 13,500 BTU unit the start spike drops from around 4,500 W to roughly 1,800 W. That reduction is exactly what lets a 2,200 W-class inverter generator start a 13.5k rooftop A/C at all. The device installs at the A/C unit itself, wired in with the compressor's start components, and it's a one-time install per air conditioner.
Is 50 amp twice as much power as 30 amp?
It's much more than twice. A 30 amp RV connection is a single 120 V leg: 30 A × 120 V = 3,600 W total. A 50 amp RV connection is two separate 120 V legs at 50 A each: 2 × 50 A × 120 V = 12,000 W — more than three times the power. That's why a 50 amp rig can run two air conditioners, an electric water heater, and a microwave at once, while a 30 amp rig has to juggle which big loads run at the same time.
Can I plug my 30A RV into a house outlet?
Yes — a 30A-to-15A dogbone adapter lets the RV cord plug into an ordinary household outlet. But the adapter doesn't add capacity: you get whatever the house circuit delivers, about 1,800 W on a 15 A circuit or 2,400 W on a dedicated 20 A one. That's enough for the converter, the refrigerator, lights, and chargers — but in most cases not enough to start and run the air conditioner. Use a single heavy-gauge (10 or 12 AWG) extension cord kept as short as practical, never daisy-chain light-duty cords, and check that the cord and outlet aren't getting warm.
Why do campground pedestals damage RV air conditioners?
On hot afternoons a crowded campground's voltage can sag well below a healthy 120 V — a brownout. When voltage drops, a compressor draws more amps to do the same work, and that extra current turns into heat in the compressor windings. Running through repeated low-voltage spells shortens compressor life and can kill the unit outright. A surge protector with EMS (electrical management system) features monitors the pedestal and disconnects on low voltage, high voltage, miswiring, or an open ground — cheap insurance compared to replacing a rooftop air conditioner.
What runs on 12V vs 120V in my RV?
An RV has two electrical systems. The 12 V DC side runs off the batteries: interior lights, vent fans, the water pump, the furnace blower (propane makes the heat, but the fan is 12 V), and control boards — including the controls on an absorption fridge. The 120 V AC side needs shore power, a generator, or an inverter: the air conditioner, microwave, wall outlets, the electric water heater element, and the converter that charges the batteries. The split matters most when boondocking without an inverter — everything on the 12 V list keeps working from the batteries, and nothing on the 120 V list does.