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For calculations of motors the code book states that a 1.5 HP motor draws 10 amps. For correct sizing the motor's nameplate amperage should be used.
Using 10 amps, 30 amp non time delay fuse, 15 amp for time delay fuse, or 25 amp for breaker. A #10 copper conductor with an insulation factor of 90 degrees C should be used on this amperage.
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ProfessorAnswer for USA, Canada and countries running a 60 Hz supply service.
The motor's amperage has to be found to answer this question.
The formula to use is I = HP x 746/1.73 x E x %eff x pf.
A standard motor's efficiency between 5 to 100 HP is .84 to .91.
A standard motor's power factor between 10 to 100 HP is .86 to .92.
Amps = 746 x 1.5/1.73 x 480 x .84 x .86 = 1119/200 = 5.6 amps
The breaker has to be sizes to 250% of the motors full load amps. 5.6 x 250% = 14 amps.
A three pole 15 amp breaker connected to three conductor 600 volt rated cable will be needed.
As for overload protection without knowing the brand of contactor it is hard to say what the proper number of the heaters will be.
To obtain the proper overload protection base the overload heaters on the 5.6 amps or the motors full load amps that will be on the motor's nameplate.
As always, if you are in doubt about what to do, the best advice anyone should give you is to call a licensed electrician to advise what work is needed.
Before you do any work yourself,
on electrical circuits, equipment or appliances
always use a test meter to ensure the circuit is, in fact, de-energized.
IF YOU ARE NOT ALREADY SURE YOU CAN DO THIS JOB
SAFELY AND COMPETENTLY
REFER THIS WORK TO QUALIFIED PROFESSIONALS.
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What size main breaker feeding 480v 75 kva transformer?
An exact breaker size can not be given because the voltage, and hence the calculation for current, is not given. A transformer shall be protected by an over current device that is not rated at more that 150% of the primary current.
What size breaker for a 20 horse power motor with 3 phase 208 volts?
For a 20 horsepower motor with 3-phase 208 volts, you would typically use a 70 amp circuit breaker to protect the motor and wiring. This calculation is based on the full load amp (FLA) rating of the motor, which for a 20 HP motor at 208 volts typically falls around 70 amps. It's important to consult the motor's technical specifications and local electrical codes to ensure proper breaker sizing.
How do you find out how big your main breaker box is?
You can determine the size of your main breaker box by looking at the number of circuits it can handle. A typical residential main breaker box is usually 100 amps, 150 amps, or 200 amps. You can also check the label on your breaker box or consult with an electrician for assistance.
What size of wire and breaker do you need for a 10 KW electric furnace?
To answer this question, wire size is rated in the amount of amperage that it can legally carry. The formula to find amperage when the HP is known is I = HP x 746/1.73 x E x %eff x pf. A standard motor's efficiency between 5 to 100 HP is .84 to .91. A standard motor's power factor between 10 to 100 HP is .86 to .92. Amps = 10 x 746 = 7460 = 7460/1.73 x 220 x .84 x .86 = 7460/275 = 27.1 amps. The electrical code states that a motor conductor has to be rated at 125% of the motors full load amperage. 27.1 x 125% = 33.8 A #8 copper conductor with an insulation factor of 60, 75 or 90 degrees C is rated at 40, 50 and 55 amps respectively.
How many amps should a starter draw?
A typical starter motor draws around 50 to 150 amps while cranking an engine. If the current draw is significantly higher or lower, it may indicate a problem with the starter motor or the electrical system.
