Generator Overload: Why the Breaker Keeps Tripping (and How to Stop It)
Overloading is the most common reason a generator’s breaker trips or an inverter generator cuts out. The good news is that it is easy to diagnose with a little arithmetic. This guide explains the two kinds of overload, how to work out your numbers and how to get everything running without tripping anything.
Why generator breakers trip
- Running overload: the total watts of everything plugged in is more than the generator (or a single outlet) can supply continuously.
- Starting surge: motors and compressors briefly draw two to three times their running watts when they start. If the surge exceeds the generator’s starting (surge) rating, the breaker trips or the engine bogs down.
- A short circuit or ground fault: a damaged cord or faulty appliance makes the breaker or GFCI trip immediately, even with a small load.
The math: amps and watts
Amps = watts ÷ volts, and watts = amps × volts. Our watts to amps calculator does it for you.
| Outlet or breaker | Voltage | Maximum watts | Continuous load (80%) |
|---|---|---|---|
| 15 A household-style outlet | 120 V | 1,800 W | 1,440 W |
| 20 A outlet | 120 V | 2,400 W | 1,920 W |
| 30 A (L5-30 or TT-30) outlet | 120 V | 3,600 W | 2,880 W |
| 30 A (L14-30) outlet | 240 V | 7,200 W | 5,760 W |
| 50 A outlet | 240 V | 12,000 W | 9,600 W |
A generator rated 7,500 running watts can still trip a 20 A outlet breaker if more than 2,400 W is plugged into that outlet. Spread loads across outlets and legs.
Step by step: stop the trips
- Unplug everything and reset any tripped breaker and GFCI. If it trips again with nothing plugged in, the generator has a fault. Stop and have it checked.
- List your loads with running and starting watts. Check the appliance label or our appliance wattage chart.
- Add up the running watts. Make sure it is below the generator’s rated running watts, leaving about 20% headroom.
- Find the largest starting surge and add it to the running total. That must be below the generator’s starting (surge) watts. The generator size calculator does this for you.
- Start the biggest motor first, then add smaller loads one at a time. Let each load settle before adding the next.
- Balance 120 V loads across the two legs of a 120/240 V generator, so that one half is not overloaded.
Example
A generator rated 3,500 running watts and 4,000 starting watts powers a refrigerator (700 W running, 2,200 W extra to start), a sump pump (1,050 W running, 2,200 W extra) and lights and internet (200 W).
- Running total: 700 + 1,050 + 200 = 1,950 W. That is comfortably under 3,500 W.
- If both motors start at the same moment (common when power is restored): 1,950 + 2,200 + 2,200 = 6,350 W. That is far above the 4,000 W starting rating, so the breaker trips.
- If you stagger the starts: the worst case is one motor starting while everything else runs, 1,950 + 2,200 = 4,150 W. That is just over 4,000 W, so expect an occasional trip.
Staggering fixes the big problem, but this setup is still marginal. Switch off other loads while the pump or refrigerator starts, or choose a generator with at least 4,500 starting watts.
Common overload triggers
- Air conditioners, especially in summer. Window units and RV roof units can need three to four times their running watts at start.
- Well pumps, sump pumps and refrigerators starting at the same time after the power returns.
- Electric heaters, kettles and microwaves, which draw their full wattage continuously.
- Power tools with high starting current, such as table saws and compressors.
Fixes that work
- Stagger the starts and avoid turning everything on at once.
- Drop big loads you do not need. Skip the electric kettle and dryer on a small generator.
- Use soft starters on air conditioners and some pumps to reduce starting current.
- Use heavier extension cords to cut voltage drop. See our wire size calculator and cord gauge tips in our connection guide.
- Move up a size if you routinely hit the limit. Estimate with our load calculator.
What not to do
- Never replace a breaker with a larger one, or bypass it. Breakers protect the wiring and the generator.
- Never use damaged or undersized extension cords.
- Never keep resetting a breaker that trips right away. Find out why.
- Do not run the generator at 100% for hours. Aim for about 50 to 80% of rated output.
Inverter generators and the overload light
Inverter generators protect themselves by shutting off AC output with an overload light. Turn the generator off, unplug the loads, wait a minute, restart and add loads again. Repeated overloads cause heat and wear.
Frequently asked questions
Why does my generator trip when I plug in a refrigerator?
The compressor surge can be about three times the running watts. Combined with other loads, this can exceed the starting rating.
Why does the generator’s GFCI keep tripping?
Moisture, damaged cords and ground faults in appliances are the usual causes. Dry the cord and plugs, move them off wet ground and test another appliance.
How much power can I take from one outlet?
A 20 A, 120 V outlet is limited to 2,400 W maximum and about 1,920 W continuous, regardless of the generator’s total output.
How do I know what size generator I need?
Add your running watts and the largest surge, then add 20% headroom. Use our size calculator.
Related guides
Figures are typical planning values. Check your generator’s manual and appliance labels for exact numbers.
