Electric Motor Lifetime Cost Calculator

Two percent

Take a 5 HP motor running one shift. At 75 percent load and 13 cents a kilowatt hour it burns about $830 of electricity a year, roughly $8,300 over ten. The motor itself cost $650. So the sticker is 7 percent of the ten year bill at one shift, and under 2 percent on a machine that runs around the clock. That's the whole case for looking at efficiency, and it's why the calculator leads with the breakeven month rather than the price difference.

Where the efficiency numbers come from

Full load nominal efficiency is stamped on the nameplate of any motor built since the late nineties. If you can read it, type it in. The presets are the NEMA MG1 nominal tables for TEFC 1800 rpm motors: Table 12-12 for NEMA Premium, Table 12-11 for the older Energy Efficient grade, and a typical figure for pre-1997 standard motors, which were never tabulated and vary. Single phase compressor duty motors are a different animal, usually 70 to 82 percent, and that gap is a large part of why three phase is cheaper to run when you have it.

What this leaves out

Part load efficiency, which falls off below about half load. Power factor, which affects demand charges on some commercial tariffs. Starting current, which matters for a compressor more than for most loads. And the thing that usually decides it in practice: whether the motor fits the base and the pulley you already have. A premium motor that needs a new frame adapter and a pulley has eaten its first two years of savings before it's wired.

Use the breakeven as a sanity check, not a quote. If a motor on the list above has the efficiency on its nameplate photo, we'll confirm it, or match the one on your compressor from the motor collection.