Electric Motor Fuse Sizing Chart

Motors are usually protected by both fuses or circuit breakers and by heater coils in a magnetic starter.

Electric motor fuse sizing chart.

Keep in mind that the breaker size should not increase the max amperage rating of cable and wire. The maximum safe current limit is 80 of the rated size of breaker except some motors. This fuse sizing is normally large enough to allow the. Voltage enter the voltage at the source of the circuit.

Select motor size from horsepower column making certain you are in the correct voltage. 430 250 covering standard speed ac motors with normal torque characteristics. If motor running protection will be provided by the fuses select fuse ratings for correct type of motor from motor protection table columns headed without overload relays. Select fuse or breaker size from column 3 or 4.

The wire breaker and fuse sizes are provided as a reference for the installer and are based on the 1996 national electrical code. Heater coils provide a delay and open the circuit if the average current over a period of time is greater than the circuit is designed for. Fuses sized in accordance with column 4 must be used in conjunction with properly sized motor overload protection such as overload relays or solid state motor controllers 430 32. Fuses open the circuit quickly in case of a massive overload or short circuit.

The largest size fuse shown in the chart is the 5ag or midget a name adopted from its use by the electrical industry and the national electrical code range which normally recognizes fuses of 9 16 x 2 as the smallest standard fuse in use. Motor full load amps are taken from motors currently used by champion. Read horizontally to the right until the distance is as great or greater than your installation. A motors with 1 15 service factor or temperature rise not over 40 degrees c size fuses at not more than 125 of the motor nameplate current rating.

Amperes enter the maximum current in amps that will flow through the circuit. For motors it is recommended to multiply the nameplate fla by 1 25 for wire sizing. This fuse sizing is normally large enough to allow the overload protective device to operate on overloads without opening the fuse. Single phase voltages are usually 115v or 120v while three phase voltages are typically 208v 230v or 480v.

B best protection is obtained by measuring motor running. Fuse ratings for motors with special characteristics may need to vary from given values. Chart to determine fuse breaker and wire sizes for electric motors for single phase a c. Tection for motor branch circuits 430 52 but typically are not the maximum allowed.

In some cases this smaller amp rating. Below is the given chart showing the of max current rating of breaker size for different types of load currents. The following table gives wire breaker and fuse sizes based on horsepower voltage and phase.