Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

This is an AMP page - Open full page! for all features.

Electrical Motors - Service Factors

Sponsored Links

The service factor - SF - is a measure of periodically overload capacity (Design Power) at which a motor can operate without damage. The NEMA (National Electrical Manufacturers Association) standard service factor for totally enclosed motors is 1.0.

A motor operating continuously at a service factor greater than 1 will have a reduced life expectancy compared to operating at at its rated nameplate horsepower.

NEMA Service Factor at Synchronous Speed (rpm) for drip proof motors:

Electrical Motors - Service Factors vs. Power and Speed
Motor Power
(hp)
Service Factor - SF
Synchronous Speed (rpm)
360018001200900
1/6, 1/4, 1/3 1.35 1.35 1.35 1.35
1/2 1.25 1.25 1.25 1.25
3/4 1.25 1.25 1.15 1.15
1 1.25 1.15 1.15 1.15
1 1/2 and up 1.115 1.15 1.15 1.15

Design Power vs. Motor Power and Service Factor can be expressed as

PD = SF P     (1)

where

PD = design power (hp, W)

SF =service factor

P = motor power (hp, W)

Example - Design Power vs. Service Factor

A 1 HP motor with a Service Factor - SF= 1.15 can operate at

PD = (1 hp) x 1.15

    = 1.15 hp

without overheating or otherwise damaging the motor if rated voltage and frequency are supplied to the motor.

Insulation life and bearings life are reduced by the service factor load.

Sponsored Links

Related Topics

Electrical

Electrical units, amps and electrical wiring, wire gauge and AWG, electrical formulas and motors.

Related Documents

Belt Transmissions - Speed and Length of Belts

Calculate length and speed of belt and belt gearing.

Belts - Power Transmission and Efficiency

Calculate belts power transmission and efficiency

Electric Motors - Efficiency

Calculate electric motor efficiency.

Electrical Induction Motors - Torque vs. Speed

Full load operating torque vs. break down, pull up and locked rotor torque.

Three-Phase Electrtical Motors - Power Factor vs. Inductive Load

Inductive loads and power factors with electrical three-phase motors.

Three-Phase Power - Equations

Electrical 3-phase equations.

Sponsored Links

Search Engineering ToolBox

  • the most efficient way to navigate the Engineering ToolBox!

SketchUp Extension - Online 3D modeling!

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with the amazing, fun and free SketchUp Make and SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp from the Sketchup Extension Warehouse!

Privacy

We don't collect information from our users. Only emails and answers are saved in our archive. Cookies are only used in the browser to improve user experience.

Some of our calculators and applications let you save application data to your local computer. These applications will - due to browser restrictions - send data between your browser and our server. We don't save this data.

Google use cookies for serving our ads and handling visitor statistics. Please read Google Privacy & Terms for more information about how you can control adserving and the information collected.

AddThis use cookies for handling links to social media. Please read AddThis Privacy for more information.