Enter the total horsepower (hp), the voltage (volts), the power factor, and the efficiency into the calculator to determine the Current From HP.
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Current From HP Formula
The following formulas are used to calculate the Current From HP (using 1 hp ≈ 746 W).
Single-phase (or DC): I = (HP × 746) / (V × PF × η)
Three-phase: I = (HP × 746) / (√3 × V × PF × η)
- Where I is the current (amps)
- HP is the mechanical power output in horsepower (hp)
- V is the voltage in volts (RMS; for three-phase this is typically the line-to-line voltage)
- PF is the power factor (unitless, typically 0 to 1 for AC loads)
- η is the efficiency (unitless, 0 to 1)
To calculate current from horsepower, convert horsepower to watts (HP × 746) and divide by the product of voltage, power factor, and efficiency (and also divide by √3 for three-phase systems).
| Horsepower (HP) | Current at 120 V (A) | Current at 240 V (A) | Current at 480 V (A) |
|---|---|---|---|
| ¼ | 2.03 | 1.02 | 0.51 |
| ⅓ | 2.71 | 1.35 | 0.68 |
| ½ | 4.06 | 2.03 | 1.02 |
| ¾ | 6.09 | 3.05 | 1.52 |
| 1 | 8.13 | 4.06 | 2.03 |
| 1½ | 12.19 | 6.09 | 3.05 |
| 2 | 16.25 | 8.13 | 4.06 |
| 3 | 24.38 | 12.19 | 6.09 |
| 5 | 40.63 | 20.32 | 10.16 |
| 7½ | 60.95 | 30.47 | 15.24 |
| 10 | 81.26 | 40.63 | 20.32 |
| 15 | 121.90 | 60.95 | 30.47 |
| 20 | 162.53 | 81.26 | 40.63 |
| 25 | 203.16 | 101.58 | 50.79 |
| 30 | 243.79 | 121.90 | 60.95 |
| 40 | 325.05 | 162.53 | 81.26 |
| 50 | 406.32 | 203.16 | 101.58 |
| 60 | 487.58 | 243.79 | 121.90 |
| 75 | 609.48 | 304.74 | 152.37 |
| 100 | 812.64 | 406.32 | 203.16 |
| Single-phase formula: I (A) = (HP × 746) / (V × PF × η). Assumes PF = 0.90 and efficiency η = 0.85. For three-phase (using line-to-line voltage), I = (HP × 746) / (√3 × V × PF × η). | |||
How to Calculate Current From HP?
The following example problem outlines how to calculate Current From HP.
Example Problem #1
- First, determine the total horsepower (hp). In this example, the total horsepower (hp) is 10 hp.
- Next, determine the voltage (volts). For this problem, the voltage is 240 V.
- Next, determine the power factor. In this case, the power factor is 0.85.
- Next, determine the efficiency. For this problem, the efficiency is 0.90.
- Finally, calculate the Current From HP using the formula above (single-phase):
I = (HP × 746) / (V × PF × η)
Inserting the values from above and solving yields:
I = (10 × 746) / (240 × 0.85 × 0.90) = 40.63 (amps)
FAQ
What is horsepower (HP) and how is it related to electrical current?
Horsepower (HP) is a unit of power commonly used to describe mechanical output power from motors and engines. When a motor is powered electrically, you can estimate the electrical current it draws from its mechanical horsepower, voltage, power factor, and efficiency. For single-phase systems, a common estimate is: I = (HP × 746) / (V × PF × η). For three-phase systems (using line-to-line voltage), use: I = (HP × 746) / (√3 × V × PF × η).
Why is the power factor (PF) important in calculating current from HP?
Power factor (PF) is the ratio of real power (kW) to apparent power (kVA) in an AC circuit. A lower power factor means more current is required to deliver the same real power, which increases the electrical load on conductors and equipment. That’s why PF appears in the denominator of the HP-to-current formulas.
How does efficiency (η) impact the calculation of current from HP?
Efficiency (η) is the ratio of mechanical power output to electrical power input (expressed as a decimal from 0 to 1). Lower efficiency means more electrical input power (and therefore more current) is required to produce the same mechanical horsepower, so η also appears in the denominator of the current calculation.
