![]() Construction of 3 Phase Induction Motor. ![]() Visit the Terms of Use and Privacy Policy for this site. Therefore, the heater must be sized for 28 * 1.15 = 32.2 Amps.Ĭonduit size in this table is conservatively based on rigid metal conduit with some spare capacity. The full-load current of a 10 HP motor at 230V is 28 Amps. According to the NEC, the overload rating must not exceed 115% of the full-load current of the motor. Therefore, it is good practice to size the breaker at 15 Amps.Ī heater is a device that protects a motor from thermal overloads due to excess current in the windings. The breaker must be sized for 7.6 * 1.25 = 10 Amps. For example, the full-load current of a 5 HP motor at 460V These two sets of protections must be coordinated with each other to properly protect your motor and motor circuits.īreaker size must be rated for a minimum of 125% of the full-load current of the motor it is protecting, rounded up to the next standard breaker size. The second is to protect the motor windings due to thermal overloads from excess current. This is called circuit protection, or feeder protection. The first is to protect the cable supplying the motor, the power source, and any components upstream on theĬircuit from the motor. There are typically two different sets of protections to design for when designing motor circuits. Motor Nameplate Voltages versus Nominal System Voltages Motor Nameplate Voltage The nominal system voltage for a motor will be above the nameplate voltage to compensate for any voltage drop in the circuit. Some exception occur to this rule, such as if the motors are interlocked and cannot operate at the same time. Rating of the wire feeding the circuit must exceed 15 + 15 + (15 * 1.25) = 48.75 Amps. For example, if there are three 15-amp motors in the circuit, the ampacity ![]() Of the wire must be at least 125% of the full-load current of the largest motor, plus the sum of full-load currents for the rest of the motors. For circuits with multiple motors, the ampacity rating The NEC requires circuits supplying single motors to have an ampacity rating of greater than or equal to 125% of the full-load current rating of the motor. See Maximum Allowable Ampacities for Conductors in Raceway, Cable or Earth (30☌) for other insulation ratings. Note: The wire size in this table is based on 75☌ terminationsĪnd insulation. Full-Load Current and Circuit Protection Data for Three-Phase AC Motors Motor Horsepower The chart below displays information for motor wire size, breaker size, thermal overload ratings, and other data for ![]()
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