Work & Power

We've talked about the relationships that govern the movement of electricity through a conductor. Now we want to put that electrical energy to work.

In technical terms, work is defined as a force moving a mass over a distance. So units used to quantify work have both a distance and a weight element. In the U.S., we measure work in ft-pounds. If the horse, in the illustration shown here, were to lift the 100 lb. box one foot, it will have performed 100 ft-pounds of work. If it were to lift the box 10 ft., it will have performed 1,000 ft-pounds of work.

Now imagine two horses, each with its own box to lift, working side by side. One quickly lifts its box to 11 ft., while the other plods forward, taking twice as long to do the same job. Even though they both did the same amount of work, the first horse seems to have done more than the second horse. That's where the notion of power comes into play. Power adds an element of time to the measurement of work. Power is essentially the amount of work done in a period of time.

In mechanical applications, we measure power output in horsepower - defined as the ability to perform 550 ft-pounds of work in one second. Therefore, if the fast horse lifted the 100 lbs. 11 ft. in one second it will have generated two horsepower:

100 lbs. x 11 ft./1 second = 1,100 ft-pounds/1 second = 1,100 ft-pounds/second

The other horse, however, took two seconds to perform the same work, generating only one horsepower:

100 lbs. x 11 ft./2 seconds = 1,100 ft-pounds/2 seconds

In electrical units, 1 hp equals 746 watts.

In summary:

• Work involves moving an object over a distance.
  
• 0 pounds lifted 10ft. equals 1,000 ft-pounds of work.
  
• Power defines work performed in a given time period.
  
• One horsepower equals 550 ft-pounds per second.

And furthermore . . .

Power Factor
Rotational Energy
Direct Current Generation
Single-Phase Alternating Current
Nominal System And Equipment Voltage Ratings