Quick answer: Yes, and by a wider margin than you have been told. A 1/3 HP pump’s published starting figure is 920 VA — not the 1,200 to 2,900 W the charts quote — and the smallest 1,000 Wh station on the shelf offers 3,000 W of surge. Starting was never the power station sump pump problem. Duration is.
Every page that answers this question answers it about the surge, and every one of them gets the surge from the same place: a rule of thumb. Multiply the running watts by three to five, the rule says, and size your inverter for that. The trouble is that the manufacturer who actually publishes the number disagrees with the rule on every pump in its catalogue. For the wider decision, our power station sizing guide covers every tier.
One manufacturer in three publishes the figure at all
Locked rotor amps — the current a motor draws in the instant before it turns — is the honest name for a sump pump’s starting draw. Liberty prints it for every model in its engineering specifications, alongside full load amps, in a table headed Electrical Data. Zoeller publishes full load amps and no locked rotor at all. Wayne’s own product page for its 3/4 HP model publishes neither: the electrical specification is the phrase “PSC, Oil-Filled 3/4 HP Motor”, and its manual carries no amps table either.
So the number the whole internet quotes with confidence is published by one maker in three. Here is what that one says, at 115 V, which is the variant a 120 V power station can feed.
| Pump | HP | Full load | Locked rotor | Running ceiling | Starting |
|---|---|---|---|---|---|
| Liberty 250 | 1/3 | 5.2 A | 8 A | 598 VA | 920 VA |
| Liberty 280 | 1/2 | 8.0 A | 23 A | 920 VA | 2,645 VA |
| Liberty 290 | 3/4 | 10.4 A | 24 A | 1,196 VA | 2,760 VA |
Set those against what a station offers. The 1,000 Wh class ships 3,000 to 3,600 W of surge and the 2,000 Wh class 4,400 to 6,000 W. Every published sump pump figure above clears the smallest of them. The 3/4 HP, the biggest pump most houses will ever have, asks for 2,760 VA against 3,000 W.
The multiplier is the part that is wrong
Divide each pump’s locked rotor by its own full load and the ratio is 1.54 on the 1/3 HP, 2.88 for the 1/2 HP and 2.31 for the 3/4 HP. Not three to five. Not even consistent: within one manufacturer’s own line the multiplier varies by a factor of nearly two, and it does not rise with horsepower — the middle pump has the highest ratio of the three.
A multiplier that swings that far inside one catalogue is not a property of sump pumps. It is a property of individual motors, and it is why starting watts and running watts are separate columns, not one column times a number. Applied to the 1/3 HP — the pump most houses have — the rule predicts 1,794 to 2,990 VA where the maker publishes 920.
Power station sump pump runtime: minutes, not watts
A sump pump is not a load you run. It is a load that runs itself, when the water rises, for as long as it takes. Hours of runtime is the wrong unit; minutes of actual pumping is the right one, and that is simple division once you have a running figure.
| Pump | Running ceiling | 1,000 Wh station | 2,000 Wh station |
|---|---|---|---|
| 1/3 HP | 598 VA | 80 minutes | 161 minutes |
| 1/2 HP | 920 VA | 52 minutes | 104 minutes |
| 3/4 HP | 1,196 VA | 40 minutes | 80 minutes |
How many hours of storm those 80 minutes cover is the question we cannot answer, and neither can anyone else. No manufacturer and no standard publishes a duty cycle for a sump pump, because it is set by your pit, your water table and the rain. The figures circulating in plumbing articles run from two cycles an hour to sixty — a factor of thirty, with pages contradicting each other inside the same search results. We are not going to add a thirty-first.
What the table does tell you is the shape of the decision. If your pump runs a minute in every ten, a 1,000 Wh station is most of a night. If it runs continuously, it is 80 minutes and then nothing, whatever the surge rating says. That is why our sizing guide puts a sump pump in the 5 kWh tier: not because smaller units cannot start one, but because starting it was never the hard part.
How we calculated this
Volt-amperes are amps times volts, at the 115 V those models are rated for. Volt-amperes are not watts: a motor’s power factor makes the real watts lower, so treating VA as watts overstates the draw and understates the runtime. That is deliberate, and it is why the column is headed ceiling. Minutes are nameplate watt-hours times 0.8, divided by the running ceiling. The 0.8 is our planning figure, taken from the runtimes one manufacturer publishes for its own product.
The 230 V versions have their own figures — the 1/2 HP is 12.5 A locked rotor, or 2,875 VA at 230 V. They are irrelevant here: a portable station’s outlet is 120 V, and a pump wired for 230 V is not a load you plug in. No product was tested by us and none is recommended. Our method is described at how we test.
Before you rely on this in a flooding basement
Standing water and mains electricity together are a hazard that no runtime table addresses. Do not enter a flooded basement to reach a pump or a power station. Do not wire a station into your home’s circuits, and never feed a house through a wall socket — that is backfeeding and it can kill line workers. A transfer switch is electrician work.
A sump pump on a dedicated circuit is there by design. Moving it to an extension lead, even temporarily, is a decision to take with a licensed electrician rather than from a chart.
Frequently asked questions
What size power station do I need for a sump pump?
For starting, smaller than you have been told: every published figure here clears the 3,000 W surge of the smallest 1,000 Wh unit. For duration, larger than you would like, because a 1/3 HP pump gets 80 minutes of pumping from that unit and a 3/4 HP gets 40. Buy the capacity for the storm, not the inverter for the surge.
How many surge watts does a sump pump need?
Liberty publishes 920 VA for its 1/3 HP, 2,645 for its 1/2 HP and 2,760 for its 3/4 HP, at 115 V. If your pump is a Zoeller or a Wayne, the honest answer is that the maker does not publish it, and the rule-of-thumb multiplier that fills the gap is wrong by a factor of two on the pumps where we can check it.
Why do other sites say I need 3,000 surge watts for a 1/3 HP pump?
Because they multiply running watts by three to five. On the pumps where the manufacturer publishes both numbers the real multiplier is 1.54, 2.87 and 2.31, so the rule overshoots every time and by most on the smallest pump. It also, conveniently, points at a larger station.
Is a sump pump harder to start than a fridge or a well pump?
Easier than both, on the published figures. A refrigerator compressor’s inrush runs to 4,626 VA and a well pump far past that. The sump pump has the reputation because it is a motor in a basement during a storm, not because the number is large.
The short version
Look up your pump’s locked rotor amps on the maker’s specification sheet and multiply by 115. If the maker does not publish it, that is worth knowing before you trust anyone’s multiplier. Then stop thinking about surge, because the answer is almost certainly yes, and start counting the minutes your pump would actually spend running — which is the number that decides whether the basement stays dry.
This article is general information, not an installation guide and not a substitute for a licensed electrician. Electrical work on a service panel, a transfer switch or a utility connection is regulated in most jurisdictions and normally requires a permit and an inspection. Fuel-burning equipment produces carbon monoxide and must never be run indoors, in a garage or near an opening into the home.
