Sizing overload protection for motors

This allows the motor to operate at up to percent above its normal rating without causing the overload protection to trip. You must size the overload devices no larger than the requirements of 430. Size the feeder protection device.

But size the overload device no more than 1 of the nameplate FLC if:. Motors differ from other types of loads in one important way: The motor needs much more current to start than to run.

This temporary, but significant, inrush current is what complicates motor circuit protection.

The overcurrent protection device (OCPD) must accommodate inrush current while still protecting .

Understanding the key point of that article, which was that motor overload protection requires separate calculations from short-circuit and ground-fault protection, clears up a . Overcurrent protects the wire, overload protects the motor. Over load and over current protection is simple. For me it is easy to think of it this way.

The overload protects the motor , the overcurrent protects the wire. Selecting Fuses for Motor Running Protection. Based on Motor Actual Full Load Currents. Better protection is achieved when fuse ratings are based on motor actual FLA obtained from motor nameplates. Locate motor nameplate FLA in the column . Overload relays are inexpensive, but the of selecting the wrong one for the application can be catastrophic for your motor , process, or both.

This makes proper motor protection mission-critical. Do not apply this to motor overload protection. You calculated your load in VA, and the OCPDs are rated in . What size 75°C feeder conductor is required to serve two 7. AWG (b) AWG (c) AWG (d) AWG. AWG conductor is rated 50A at 75°C.

Therefore, the correct answer is (d), AWG. This section of Article 4includes definitions, terminology, and the required marking for motors. Important information can be found on the motor nameplate including but not limited to full load and locked rotor current, service factor and inverter duty rated. Proper sizing of overload protection in Part III.

The user manual for each VFD drive lists the cable length limitations based on drive size and the quality of the insulation system in the chosen motor. Branch Circuit Fuse Size , Individual Motor Loa. Service Factor or temperature rise not over Degrees C. Best protection is obtained by .