Simple Electrical Formulas

Steps In Calculating Usage Costs

1. Volt x Amps = Watts

2. Watts / 1000 = Kilowatt (kW)

3. Kilowatt (kW) x Hours Of Use = Kilowatt Hour (kWh)

4. Kilowatt Hours (kWh) x kWh rate = Cost Of Usage

Steps In Calculating VA (Volt/Amps) for UPS (Uninterruptible Power Supply) Systems

1. Total amperes of all equipment to be used on UPS. 

Rule of Thumb:

(MMX PC's average 2.8 Amps beginning 1997)

(PCs average 3.5 Amps prior to 1997)

1. If the equipment lists total watts only, use W x 1.4 to obtain VA

2. Total Amps x 120 Volts = VA (Volt Amps)

3. VA x 1.2 = Total VA

4. Choose the UPS that is rated higher than the Total VA

An example:

The average pool pump will have a rating of 7 to 10 amps and run 24 hours a day when the pool is being used. To figure the energy used to run this pump, we will first determine the amount of kilowatt-hours required for a month.

Kilowatt-hours can be found in the following steps;

Amps x volts = WATTS

10 Amps x 120 volts = 1200 Watts,

1200 Watts x 24 hours = 28,800 Watts, for one day.

28,800 Watts, divided by 1,000 = 28.8 kWh (kilowatt-hours) for one day.

28.8 kWh x 30 days = 864 kilowatt hours in one month.

864 kilowatt hours x your electric rate (Warren RECC's rate is .07) = the dollar amount.

864 x .07 = $60.48

A typical 18 cubic foot frost-free refrigerator will use approximately 720 watts when running, but only runs about 1/3 of the time; therefore, the formula must be modified by dividing by three. This will give a fair estimate, although lifestyle will still play a major role in energy use.

Calculating Watts

Volts x Amps = (Watts)

Calculating Amperes

Watts / Volts = (Amps)

Calculating Volts

Watts / Amps = (Volts)

Calculating Resistance (Ohms)

Volts/ Amps = R (Resistance)