Two numbers sit on every power station and inverter spec sheet — continuous (rated) watts and surge (peak) watts — and one of them is quietly deciding whether your fridge, AC, or drill will start at all. Buyers compare the first number and wonder why "it should have fit." The failure is almost always the second.

This article explains the difference in plain terms, shows the real startup numbers for the devices that matter, and gives you the two-line check that ends the "it should have run" mystery for good.

TL;DR:

●Continuous (rated) watts = what the unit delivers indefinitely. It decides how long and

whether an overload trips after a few seconds.

●Surge (peak) watts = what it delivers for seconds, for motor startups. It decides whether the device starts at all.

● A motor needs 3–6× its running watts for the first moments (inrush/locked-rotor current) — a 200W fridge can spike 600–1,000W

●Resistive loads (heaters, kettles, microwaves) have no surge — they draw flat from second one

● The two-line check:continuous ≥ everything running at once; surge ≥ your biggest motor's startup spike

The Two Numbers, Defined

Continuous (rated) watts is the output the inverter can hold forever, thermally and electrically. It's the number behind your runtime, your "what fits" question, and the overload protection: plug in more than the rating and the unit trips after a few seconds — a designed, recoverable shutdown.

Surge (peak) watts is the short-burst ceiling — typically 3–10 seconds (some units allow a few minutes at a lower peak) — that the inverter and battery can deliver above the continuous rating. It exists for exactly one reason in the real world: starting a motor.

Why a motor needs the burst: an electric motor at rest has no back-EMF, so the instant it's energized it's close to a short circuit across the windings — locked-rotor current runs 3–6× the running current until the rotor spins up and the back-EMF builds. A fridge compressor rated 200W will pull 600–1,000W for the first half-second of every start. That spike is what your surge rating must absorb — or the start is refused.

The Real Startup Table

Two patterns carry the whole article: anything with a motor or compressor has a spike; anything that makes heat or light doesn't. And the inverter-AC footnote matters — inverter compressors start softly (no locked rotor), which is why inverter ACs are the friendly column of the [AC guide].

What Happens When You Exceed Each Number

This is the diagnostic that solves most "it should have run" stories:

Exceeds continuous (but within surge): the device may start, run for seconds, then the station trips with an overload code and restarts in a minute or so. You can recover by unplugging part of the load. Signature: "it started, then shut down."

Exceeds surge: the protection triggers at the instant of startup — the device never turns on, often with a brief click or a "peak overload" indicator. No running-then-tripping; just refusal. Signature: "it won't start."

One device fits, the combo doesn't: two devices each under the rating, running together over it — e.g., a 900W grill + a 900W fan + everything else = 1,900W+ of continuous draw on a 1,800W-rated station. Overload trip, no mystery. Signature: "works alone, dies together."

All three are designed protections, not faults — the unit is doing its job, and the fix is always a load or a size change, never a repair (full behavior explained in our [safety guide]).

How to Read the Spec (the Ratio Is a Hidden Spec)

Every station publishes both numbers — and the ratio between them tells you the machine's character:

●2,000W rated / 4,000W surge (2:1) — the common mid-range design; handles fridges, small ACs, drills

●1,600W rated / 3,200W surge (2:1) — same character, smaller

●1,000W rated / 1,800W surge (1.8:1) — the entry tier where a 12,000 BTU window AC's 3,000W spike does not fit— the most common spec-sheet misread in the category

● Some home-backup-class units go 3:1 or more for well pumps and hard motors

Two things to verify beyond the ratio:

1. Surge duration. "4,000W surge" for 3 seconds covers a compressor start; a station that only allows 2,000W for a sustained 2 minutes is a different tool. The spec usually says; if it doesn't, ask.

2. Whether the surge rating assumes a full battery. A few designs derate surge output when the state of charge is low — fine at kickoff night, relevant at hour 30 of an outage.

The Two-Line Check (Print This)

Before any device plugs in, run the two lines:

Line 1 — Continuous: Sum of everything that runs at the same time ≤ station's rated watts (with 10–20% headroom). Line 2 — Surge: The single biggest motor's startup spike (running W × 3–6) ≤ station's surge watts.

Worked example — a home backup with fridge + grill + fan:

● Line 1: fridge 200 + grill 1,000 (brief) + fan 40 + lights 30 + router 15 = worst case ~1,285W → needs a 1,500W+ rated station

● Line 2: the fridge's ~800W spike (the grill is resistive, no surge) → needs≥800W surge— any station above 1,000W rated clears this easily

The grill set Line 1; the fridge set Line 2. Different devices set different lines — that's the whole discipline, and it's why "my load is only 800W, why does it need a 2,000W station?" is usually answered by the device that runs next to it, not the one that started it.

(The same two lines govern standalone inverters — the full sizing method is in our [inverter sizing calculator].)

Frequently Asked Questions

What's the difference between surge and continuous watts? Continuous is the output the inverter holds indefinitely; surge is the short (seconds) burst above it, built for motor startups. Continuous decides overload trips and runtime; surge decides whether a motorized device starts at all.

Why does my fridge trip a power station that "should" handle 200W? The 200W is its running draw; every compressor start spikes 600–1,000W for a moment. If the station's surge rating is below that spike, it refuses the start; if its continuous rating is below your total simultaneous load, it trips after running. Check both numbers against both lines.

Do all devices need surge headroom? No — only motors and compressors (fridges, ACs, pumps, drills). Resistive loads (heaters, kettles, microwaves, incandescents) draw flat from the first second with no spike, so they never set the surge line.

How long is the surge window? Typically 3–10 seconds at the rated peak (some units offer a longer, lower secondary peak). A compressor start is under a second, so the window is generous — but a sustained 2,000W draw is a continuous question, not a surge one.

Which number do I compare to my total load? Continuous — the sum of everything running at once must fit the rated output (with headroom). The surge number is compared to your single biggest motor's startup spike. Mixing the two comparisons is how the "it should have fit" mistake happens.

Final Thoughts

"Surge vs continuous" is really one question in two numbers: can this unit carry my load forever, and can it absorb the first violent second of a motor? The continuous rating governs everything you can run at the same time; the surge rating governs whether the biggest motor gets to start. Learn the startup table (motors spike 3–6×, resistive loads never do), read the ratio hidden in the spec, and run the two-line check before any device plugs in — and the entire family of "it should have run" failures, which is most of the category's support tickets, quietly disappears. The station isn't under-powered; the spec sheet just has two doors, and now you know which one your device walks through.

[Optional CTA: NEJoye stations publish rated and surge output up front — sized to clear compressor starts, not just running watts → NEJoye Power Inverters]