Separator Bible

A brief explanation on how the amperage of a device is calculated.
Resistive Load
• Resistive loads are typically those in which electricity produces heat or light, or both, rather
than movement. Typical examples of resistive loads include incandescent light bulbs and
immersion heaters.
Inductive Load
• Inductive loads are loads from electrical devices in which electricity circulates through
wound or coiled wire. Typical examples of inductive loads include motors, relays, solenoids
and transformers. The rule of thumb is if the load has movement it is generally inductive.
The power used by a resistive load can be calculated with the formula P = V x I, where P represents
power, measured in watts, V represents voltage, measured in volts, and I represents current,
measured in amperes, according to Ohm’s Law.
Example 1:
If we take an electric kettle running on 240 volts single phase at 12.5 amperes we get 3000 watts
V x I = P 240 x 12.5 = 3000
However, the power of an inductive load cannot be calculated in the same way because an inductive
load returns some of the energy used back to the source. A resistive load uses 100 percent of its
power to produce work, whereas an inductive load uses some power to operate—in the case of an
electric motor, to magnetize the core—and the remainder to produce work.
We have a 1.1 Kilowatt 3 phase 4 pole electric motor running on a 415 volt 3 phase power supply
Kw x 1000
1100 Watts
√3 x V x pf 1.73 x 415 x 0.65
= 2.357 Amperes, this is rounded up to 2.40 A
√3 = the square root of 3
(V = Voltage) 415 is the line to line voltage, the voltage between two of the three phases L1 & L2
(pf =Power Factor)
Ohm's law states that the current through a conductor between two points is directly proportional
to the potential difference across the two points. Introducing the constant of proportionality,
the resistance one arrives at the usual mathematical equation that describes this relationship:
In circuit analysis, three equivalent expressions of Ohm's law are used interchangeably: