3 Phase Power Equation

P = I x E x 1.73 x power factor. (The power factor for a resistive load is 1)

To find Amps if Power (watts) and Voltage are known for a 3-phase element, use the following equation:

I (amps) = P (watts)/Voltage x 1.732

Example #1 (24 KW, 480 VAC 3 Phase Boiler)

Solve for current flow given a 24KW, 480 VAC 3-phase heating element

24,000/480×1.732 = 24000/831.36 or 29 amps

Example #2 (48 KW, 480 VAC 3 Phase Boiler)

Larger boilers have multiple elements with individual power ratings that add up to the total boiler power. For example, a Sussman 48KW stand-alone boiler has 3 heating elements and two contactors. One contactor is wired to an 18KW element and a 12KW element, with the other contactor wired to an 18KW element. All three add up to a total of 48KW.

Using the equation from Example #1 above, one can determine that each 18KW element should draw 21.6 amps, and the 12KW element should draw 14.5 amps. Together, these add to a total amp draw of about 58 amps. This is the amp rating of a 48KW, 480-volt, 3-phase boiler.

Note – It is important to verify the electrical rating of an element to be replaced. An easy way to remember the factor “1.732” in the 3-phase power equation: 1.732 is the square root of 3.

Have a question or having difficulties? Talk to Dave Schall, our PRIMUS sterilizer expert who is here to assist you anytime at 877.679.7800 extension 1212 or email at dschall@spire-is.com.

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