Why does my power station shut off when the pump or fridge starts?
Power basics Updated 2026-08-15
Because a motor does not draw its running watts at the instant it starts. For a fraction of a second the rotor is not turning yet, the motor looks close to a short circuit, and it pulls locked-rotor current — several times its running current. Your machine is comparing that spike against its surge ceiling, not against its continuous rating, and it trips before the appliance ever reaches its running load.
That is why a pump rated well under a station’s continuous output still refuses to start on it, and why the fix is a bigger surge ceiling or a lower inrush — never a bigger battery.
Three loads, three completely different starts
Published start-up figures
Each of these comes off a manufacturer document for a specific model, with the ratio the document itself supports. The spread is the point: "motors need two to three times their running watts" is a rule of thumb that is wrong about every row below.
Real power, off the maker’s own table: Little Giant’s 6-CIA order information prints a Full Load Watts column, and 720 W is what stands in it — not a figure converted from current.
We read 3 documents for the other pumps this record cites on 2026-08-08 and found no published watt figure in them. Their spread is carried as apparent power instead, 598 to 1,116 VA, because current is what their makers do print — which is why this row is a single figure and not a band.
See the load record →From the locked-rotor amps printed on the same row of the same sheet.
Locked-rotor amps divided by full-load amps, both from the maker.
A rotary compressor, and the reason an RV air conditioner is the hardest common load to start.
See the load record →Quoted by the compressor manufacturer, not estimated.
Also a compressor — but a variable-speed one with its own electronic drive, which ramps instead of slamming. Same appliance category, no inrush at all.
See the load record →Not a motor: this is the input capacitors of a switching supply charging, over tens of milliseconds. It is a much larger multiple than any pump and matters far less.
See the load record →Official spec + Derived from official coefficientsverified 2026-08-01appliance records
Duration is why the last row is harmless and the first two are not. A capacitive inrush is over in a few line cycles; a motor start lasts hundreds of milliseconds, which is inside the window any surge rating is meant to cover. Our engine bands them by their published duration and enforces them differently, rather than treating every spike as equal.
The rule of thumb that oversizes by three times
The standard tables used to size breakers and motor controllers publish locked-rotor envelopes for each horsepower class. Those envelopes are deliberately generous — they exist so a protective device never nuisance-trips. Read as an appliance figure they are badly wrong in the expensive direction: for the pump above, the code envelope is more than twice what the pump maker measured on its own product. Where we have only an envelope value we label it as one and cap the confidence, because sizing a backup supply off it means buying two or three times the machine you need.
What that does to a verdict
One sump pump, three machines
Live engine runs. The percentage is the running load as a share of that machine’s continuous output — which is exactly why it explains nothing about the third row.
Fails before surge is even reached: the running load alone is above the inverter rating.
Show the working →Half the continuous rating, and the published surge ceiling clears the start.
Show the working →A bigger machine that says no. We have found no published surge rating for this record at all, so the engine substitutes the continuous output as a conservative floor — an inverter cannot surge below what it sustains — and the pump’s start is above it. We will not assume a ceiling nobody stated.
Show the working →The third row is not a bug and it is the most useful row on this page. The floor the engine used is 2600 W, taken from the continuous output because we have found no published surge figure for it. A site that quietly assumed "probably twice the rating" would have shown a green light there. We would rather tell you that the manufacturer has not answered the question.
A motor start no one has published
The three loads above are either a real motor or something that only looks like one at the meter. A hair dryer is a third shape: a heating element wired beside an actual motor — Conair’s own feature list for its 530-series dryer names a "Powerful motor" right next to the heat settings — so a start-up current certainly exists. Four manufacturer documents across two brands state a wattage, a supply voltage and a circuit-breaker warning for it, and we have found no published inrush, locked-rotor current or other start-up figure in any of them.
What the hair dryer’s own record holds on start-up
The same shape of absence as the Elite 200 row above, read off the appliance side of a pairing instead of the station side.
The US nameplate rating — and, not by chance, sitting above the 1,800 W this library records as the ceiling of the branch circuit it plugs into.
See the record →We read 4 documents for hair dryers on 2026-08-09 and found no published start-up figure in them.
Official specverified 2026-08-09hair dryer record
Our engine’s response to that gap depends on what kind of load this is, not on whether the gap exists. A purely resistive load with no published surge figure gets no separate check at all — the policy this library uses for a coffee maker or an air fryer, because there is no separate event left to be cautious about. This record is classed mixed rather than resistive, purely because of the motor Conair itself advertises, and our engine gives an unmeasured mixed load the same caution it gives an unmeasured motor: capped at "marginal," never "green," on every machine in the library — however much continuous output that machine has to spare.
Two machines, the same appliance, two different reasons it will not pass
Live engine runs. The second row is the one worth reading twice.
Refused before the missing start-up figure is even reached: the running load alone is above this machine’s continuous rating.
Show the working →More than double the running load in continuous output to spare, and the verdict still lands marginal — the missing start-up figure is what is capping this, not the wattage.
Show the working →