The two most important formula that you need are:

V = IR

• V is Volts (Volts)
• I is Current (Amps)
• R is the sum of the resistance (Ohms)

P = VI

• P is Power (Watts)
• V is Volts (Volts)
• I is Current (Amps)

1 Watt = 1 Joules/Second

Joules is Energy, so Power (Watts) is the rate of Energy (Joules) consumption (or production)
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Example 1:

How much current does a 100W household light globe use?
Power = 100 Watts
Voltage = 230 Volts

Current (I) = P/V = 100/230 = 0.43 Amps

Example 2:

An industrial plant uses a 1000 kWh in an 8 hour day, on average what is the required power?

1000 kWh = 1000000 Wh

P = Energy (kwh) / time (h) = 1000000/8 = 125000 Watts = 125 kW avg.

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