November 23, 2011

Users often ask how much electrical cost they will experience operating a pump or aerator motor. Simple enough to determine using information found on the motor or manufacture’s literature and a bill from their electric company.

The basic formula to calculate electric cost per hour is;

Cost per Hour = Kw x $ per KwHr

Where;

Kw Motor kilowatt rating. Find on motor label or in manufacturer literature.
$ per KwHr How much the electric company charges. Find on a recent bill or call them.

Example: A 2 Hp motor has a kilowatt rating of 2.19 Kw. Electric cost is $.09 per KwHr. So,

Cost per Hour = 2.19 Kw x $.09/KwHr equals = $.1971

Cost per day, week, month, year, etc then depends on how many hours the motor is operated in that timeframe.

Example: The above motor is operated 18 hours per day. So,

Cost per Day = 18 hr x $.1971/KwHr = $3.5478 or $3.55
Cost per Week = 18 hr x 7 days x $.1971/KwHr = $24.8346 or $24.83

Let’s say the motor plate does not list the Kilowatt Rating nor is lit listed in literature or a web site and a representative is not available to help. You can still come close, but you will have to calculate the Kilowatt Rating using the following formula;

The formula varies depending if the motor is 1-Phase or 3-Phase. How do you know? The motor plate should tell you that or your electrician can tell you.

1-Phase: Kw = I x E x Pf / 1000

3-Phase: Kw = I x E x 1.73 x Pf / 1000

Where;