Motor Efficiency Chart

Use this worksheet after the calculator result to record shaft output, input power, losses, load profile, annual kWh, operating cost, and simple payback for an efficiency comparison.

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Quick reference table

A motor efficiency chart is a calculator worksheet for turning an efficiency result into an energy and maintenance planning record. Efficiency is output power divided by input power, while project value depends on load profile, operating hours, energy rate, downtime, and replacement cost.

Efficiency result worksheet

Efficiency result worksheet
Result item	Record from calculator	Decision note
Shaft output	Output kW or HP	Confirm the load basis is the same in both cases
Input power	Measured or estimated kW	Identify current motor and proposed motor cases
Losses	Loss kW or percent	Shows heat and wasted power that may affect enclosure or cooling
Annual energy	kWh and cost values	Connects the result to operating hours and energy rate
Payback	Simple payback years	Screen against replacement, labor, and downtime cost

Efficiency comparison inputs

Efficiency comparison inputs
Input to document	Why the electrician records it	What can change the result
Load profile	Full load, part load, cycling, or standby duty	Savings can shrink when the motor rarely runs loaded
Operating hours	Annual runtime from the calculator	Seasonal process changes and production schedule
Measured input	Metered kW, estimated kW, or nameplate assumption	Measurement method and real voltage condition
Installed cost	Motor, labor, drive, alignment, and downtime cost	Procurement, outage window, and maintenance scope

Formula basis

Efficiency = output power / input power x 100%. Losses = input power - output power.

Output power is the useful shaft output in HP, kW, or watts.
Input power is the measured or estimated electrical input for the same load condition.
Losses are the difference between input power and useful output power.
Annual savings compare input kWh and cost between current and improved cases at the documented operating hours.

Worked examples

Continuous process motorA motor running most of the year can turn a small input-kW reduction into meaningful kWh savings, so the worksheet keeps load profile, operating hours, and energy rate beside the calculator result.

Standby pump with low runtimeA high-efficiency replacement may show little payback when annual hours are low, so the chart records duty, maintenance value, and downtime notes instead of judging by efficiency alone.

Assumptions. Balanced load and line-to-line voltage assumptions behind this chart.

The worksheet assumes the operating hours, energy price, load profile, and installed-cost inputs used by the calculator are documented and reviewable.
Actual savings can change with part-load operation, duty cycle, VFD behavior, maintenance condition, voltage, and utility rate structure.
Nameplate efficiency is not the same as a measured field efficiency value unless the operating point is comparable.

Code and standard notes. Planning limits that should be checked before final equipment selection.

Use this chart for energy planning; verify motor nameplate data, measured load, manufacturer efficiency data, equipment fit, and project requirements before procurement.

How to use this chart

1Record output firstStart with shaft output so input power, losses, and savings are tied to the same mechanical load requirement.

2Separate operating casesKeep existing motor, proposed motor, measured load, and assumed load cases on separate rows before comparing annual energy.

3Check payback inputsCheck operating hours, energy rate, installed cost, downtime, and maintenance assumptions before relying on simple payback.

Worksheet checklist. Record source basis, review gaps, and assumptions before using the chart result.

Capture measured caseWrite input power, output power, losses, annual hours, and annual energy for the current or measured motor condition.
Capture improved caseRecord proposed efficiency, input power, losses, energy savings, cost savings, installed cost, and simple payback.
Capture project limitsList load profile, enclosure, mounting, VFD compatibility, process downtime, and maintenance constraints that affect the decision.

Common mistakes to avoid. Review these before turning chart current into an equipment decision.

Calculating payback from full-load hours when the motor normally runs at part load, cycles on and off, or sits in standby.
Comparing nameplate efficiency values without checking voltage, duty, enclosure, VFD compatibility, and real operating conditions.
Treating lower losses as the only project value while ignoring downtime, installation cost, spare motor policy, and maintenance risk.

Frequently asked questions

These answers explain how to use the chart without turning a quick reference into a final design decision.

Why can a small efficiency gain matter?

A motor that runs many hours per year can convert a small input-power reduction into a meaningful annual kWh and cost difference.

Is simple payback enough for replacement?

No. It is a screening metric. Check load profile, downtime, maintenance, incentives, compatibility, and replacement cost before a project decision.