- What an inverter overload is
- How to tell an overload from something else
- What not to change when the inverter overloads
- Frequently asked questions
- Why does my solar inverter shut off when the pump starts?
- Is inverter clipping the same as overload?
- Can I run the house at the surge rating all afternoon?
- Sources and references
A solar inverter overload is the inverter refusing a load that is above its continuous rating, or above the surge it can hold for the seconds printed on the sheet. The fix is a smaller simultaneous load or a larger inverter that is still listed for the service. The fix is not a larger breaker. A breaker protects the wire. Upsizing it so the inverter stops tripping only removes the wire’s protection. The inverter was already telling the truth.
What an inverter overload is
Every inverter has a continuous wattage it can supply and, on many off-grid and backup units, a higher surge it can supply for a stated time. A motor can draw several times its running current for a moment while it starts. If that moment is inside the surge rating and the running watts are inside the continuous rating, the inverter holds. If either limit is exceeded, it shuts down or folds back. Those two numbers, and why a single “peak watt” line is not enough, are written for vehicles in RV inverter continuous and surge ratings. A house uses the same two numbers. The driveway is not what makes them real.
A grid-tied solar inverter overloads in a different direction as well. Its AC output is limited by its AC rating. If the array’s DC power would push more than that rating, the inverter holds the AC side at its maximum and the extra DC is not converted. That is clipping, not a tripped breaker in the kitchen. It is an array-to-inverter sizing choice. It is not solved by plugging in fewer appliances, because the appliances were not the cause. Do not treat every “inverter at 100 percent” screenshot as an overload fault. At solar noon on a clear day, a deliberately oversized array is supposed to sit on the ceiling.
Heat causes a third, related limit. Component temperatures rise with the power being dissipated. A hot inverter may reduce output before it hits the nameplate you remember from a cool morning. Clearing the air path is maintenance. Defeating the thermal limit is not. Fan and clearance checks are in how to maintain a solar inverter.
How to tell an overload from something else
An overload tracks the load. The well pump, the microwave, and the kettle together, and the inverter dies. Any one of them alone, and it runs. That pattern is the nameplate, not a failing array. A fault that appears at noon with the house idle, and disappears when a cloud arrives, is more often clipping, heat, or a DC-side limit. A fault that appears when the utility voltage sags is a grid event. A grid-tied inverter is required to stop energizing an unintentional island within 2 seconds. That stop is not an overload, and it should not be “fixed” by defeating protection.
Write down the watts you tried to run, not the emotion. Nameplate watts on appliances are not always the running watts, and a motor’s start is not printed on the front of the fridge. If you cannot measure, you can still stop stacking the large loads and see whether the trip disappears. If it does, the inverter is too small for that stack, or the stack is a habit you can change. If a single motor never starts, the surge is the suspect, not the daily energy production of the panels.
Waveform can imitate an overload. A motor that runs hot and trips on a modified sine inverter may be reacting to the stepped wave, not to a shortage of watts. Confirm the waveform before you buy a larger modified unit and repeat the problem. The distinction is in pure sine wave versus modified sine wave.
What not to change when the inverter overloads
| Tempting change | Why it is the wrong knob |
|---|---|
| A larger breaker | The breaker is sized to the wire. A bigger breaker lets the wire overheat. The inverter limit is still there. |
| More solar panels | Panels add energy over the day. They do not raise the inverter’s continuous AC rating. A surge at dusk still comes from the battery, if you have one. |
| Defeating thermal fold-back | The fold-back is the inverter protecting itself. Clearance and a clean fan are the allowed response. |
| A battery with more amp-hours, same inverter | More hours, not more watts. Overload is a power limit. A larger bank helps a load that ran and then died at midnight, which is a different complaint. |
If the right answer is a larger inverter, match the service voltage and the array’s maximum DC voltage, including a cold morning. On a backup system, also match the transfer equipment and the circuits you intend to keep. A bigger inverter on the same backup panel can start a pump the panel and the battery were not built for. Off-grid sizing is in how to size an off-grid inverter. A grid-tied house is not that design, but the rule against confusing energy with power is the same.
Frequently asked questions
Why does my solar inverter shut off when the pump starts?
The start surge is probably above the surge rating, or it lasts longer than the rating allows. The running load may be fine. A larger breaker will not start the pump. A pure sine inverter with a real surge rating might, if the battery can deliver the current. Measure before you buy.
Is inverter clipping the same as overload?
No. Clipping is the AC rating holding the output down while extra DC is available from the array. An overload, in the sense of this page, is a load asking for more AC than the inverter will give. One is a sizing choice at noon. The other is too many appliances, or one hard motor.
Can I run the house at the surge rating all afternoon?
No. The surge is a short allowance. The continuous rating is the afternoon. Running at the surge number for an hour is an overload even if the inverter survived the first minute.
Sources and references
Temperature rising with dissipated power: Sandia and NREL thermal study. A grid-tied inverter must cease to energize an unintentional island within 2 seconds: IEEE 1547-2018 primer. No breaker size and no universal surge multiple are stated. A motor’s start current belongs to that motor. The inverter’s surge belongs to its datasheet, including the seconds.
