Starting Watts vs Running Watts

Why motors need a surge and heaters do not

An electric motor at a standstill is, electrically speaking, close to a short circuit. There is no back-EMF opposing the current until the rotor is actually moving, so for a fraction of a second the motor draws everything the supply will give it. Once it is turning, the draw collapses to the running figure.

A heating element has none of that. It is a resistor: it draws the same current the instant you switch it on as it does an hour later. Which is why EWEB's chart lists a space heater at 1,500 running watts and zero additional starting watts, and a refrigerator at 700 running and 2,200 additional.

What this means for the generator's two ratings

Generators publish both numbers too, and this is where the marketing happens. A machine sold as "13,000 watts" has 13,000 peak or starting watts — a figure it can hold for a second or two. Its running figure might be 10,500.

So the rule: size the continuous load against the generator's running rating, and check your single largest surge against its peak rating. A machine with 6,500 running watts and 8,125 peak watts handles 6,500 watts of continuous load and a 1,625 watt surge on top — which is enough for a fridge only if the fridge is not the last thing you switch on.

The sequencing trick almost nobody mentions

Surge headroom depends on what is already running. If the generator is at 6,000 of its 6,500 running watts and you start a fridge, it needs 2,200 watts it does not have, and it will bog down or trip.

Start the biggest motors first, while the generator is lightly loaded, then add the steady loads. This is free, it costs nothing, and it is the single most useful operational habit in generator ownership. It is also why an interlock kit demands more of you than a transfer switch: with an interlock you control which breakers go on, and in what order.

What about soft starters

If the surge is your constraint rather than the running load — and for houses with a well pump or air conditioning it usually is — you can attack the surge directly. Soft starters ramp a motor up instead of slamming it on.

The published claims are substantial: one well-pump soft starter states it reduces inrush current by up to 50% and will start pumps on generators as small as 3,000 watts, while an AC soft starter claims up to 70% startup reduction. If either figure holds for your equipment, it can move you down a whole generator class for a fraction of the price difference.

Attacking the surge instead of buying more generator

Running a well pump on a smaller generator

SoftStartUSA SoftStart Well Pump Soft Starter

$399.00·View on Amazon

Running central AC on a generator

SoftStartRV SoftStart Home AC Soft Starter

$355.00·View on Amazon5% off

Both are installed at the equipment and are electrical work. Check the compatibility range against your pump or compressor before buying — outside it, neither does anything.

Next: the appliance wattage chart for both figures on every common load, or the calculator to apply them.