Starting Watts vs. Running Watts: Why Motors Need a Brief Boost
Simple electricity diagram
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STARTING Motor at rest → brief extra current → motor begins turning Think: the first hard push to get a bicycle moving. |
RUNNING Motor already turning → lower steady current → normal operation Think: less effort once the bicycle is rolling. |
Preparedness check: Your backup power source needs enough capacity for both the normal running load and the brief startup demand.
An appliance can look easy to power once it is running but still be difficult for a backup power source to start. The reason is simple: electric motors can draw more current during startup than during normal operation.
The bicycle analogy
Think about riding a bicycle. The hardest push is often the first one that gets the bike moving. Once you are rolling, keeping the bike moving takes less effort. A motor has a similar challenge when it starts from a stop.
The U.S. Department of Energy describes locked-rotor or startup amps as the current a motor can draw while its rotor is stopped, including during the first few seconds of startup. NEMA motor standards also treat locked-rotor current as a separate starting condition from normal operation.
Why this matters for backup power
Refrigerators, pumps, fans, and other equipment can contain motors. A portable power station or inverter might be able to support the equipment after it is running but still shut down if the startup demand exceeds the unit's output or surge capability.
Do not rely on a generic multiplier for every appliance. Motor designs and starting methods vary. Check the appliance manufacturer's specifications and the backup-power manufacturer's continuous and surge ratings.
Prepare before the outage
Make a short list of the motor-driven equipment you want to keep running during an outage. Confirm that your backup system can handle the normal load and startup demand before you depend on it in an emergency.
If your inverter or power station repeatedly trips its overload protection, reduce the load and follow the manufacturer's instructions. Never bypass overload protection or modify wiring to force equipment to run.
Preparedness lesson: Running power tells only part of the story. Planning for startup demand can prevent a surprise shutdown when you need backup power most.
Sources: U.S. Department of Energy, MotorMaster+ User's Manual; National Electrical Manufacturers Association, NEMA MG 1, Part 12.
