Amperage vs. Wattage vs. Horsepower

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How do I know if I the module I have selected has enough power?

Can horsepower be converted to amps, and vice versa?


  • The AM486 and AM466 appliance modules are both rated at 15A resistive, 1/3 HP inductive, and 500W for incandescent lamps.

Amps X Volts = Watts

  • 15A X 120V = 1800W, so the appliance modules can handle 1800W RESISTIVE, such as a coffee pot, for example. The confusion usually arises from the fact that the module is rated at only 500W for incandescent lamps. However, a lamp rated at 100W may pull up to 600 watts for a split-second when it is initially turned on. This is called "inrush current."

  • While 1HP (horsepower)= "approximiately" 750W - and the appliance modules are rated for 1/3HP, which sounds just like 250 watts. However this is the limit UL imposes for inductive loads due to their "stalled rotor test." Motors are rated for how much current they pull when they are going at full speed, not how much they draw when they start up.

  • The HD243 and HD245 heavy duty appliance modules are connected across the two 110V phases to give 220V. They do not draw any current between either leg and ground. These modules have an "unconditional" UL rating of 15A and 20A respectively and are therefore rated for ANY kind of load up to 3300W and 4400W respectively (15A x 220V and 20A x 220V).

  • The SR227 wall receptacle (which has a different relay from the AM486 and AM466) has an unconditional rating of 15A, i.e., 15A x 120V = 1800W, unconditional.