What is the equation for finding amps?

Answer 1

I find amps by measuring with a 'clamp-on' ammeter. I use this information particularly to evaluate the performance of deep well pumps. If you are looking to determine amperage using known values such as Voltage, Resistance, or Power {Wattage} you will need to use "Ohm's Law". It's the base formula from which most all other formulas regarding electricity extrapolate it's functions from.

Ohm's Law:

E = I [X] R

Where:

E=Voltage or EMF [electro motive force] in Volts or "V"

I=Current in Ampere as "A" or Amps,

R=Resistance in Ohm's as "R" or the Omega symbol

From thew known characteristics of E, I, and R another formula of Ohm's law can be used to determine power using two known values.

Ohm's Law Power Formula:

P = I [X] R

Where:

P=Power in Wattage/Watts as "W"

I=Amp

E=Volts

Examples:

You have a portable car heater {a heating element is just a large resistor for simplicity} and the specifications on its label says he device is a 12 volt appliance that uses 60 Watts of power You are asked to determine what size wire will be needed and the total resistance of the circuit.*

Wire is sized for the amount of current ** it will be required to handle giving as little resistance {i.e. heat} as possible, but not over sized wasting the customers or your own money. Using the given values for E and P we can determine I.

If,

P = I X E then,

60Watts = I {Amps} [X] 12 Volts so,

60 = {I} [X] 12 or,

{I} = 60/12 therefore,

{I} = 5 Amps

As a construction electrician we seldom are required to calculate for anything smaller than 14 guage wire {rated at 15 amps per code} so I am only guessing at 5 amps but I'm sure it is close to 22-24 AWG seeing 18 is good for 14 amps in fixture wiring.

Then:

If,

E-I x R then,

12Volts = 5Amps {from above} [X] R so,

12 = 5 X {R} therefore,

R = 12/5 therefore,

R = 2.5Ohm's

Thus:

The device is a 12 Volt heater that uses 60 Watts of power that allows 5 amperes of current through the circuit that produces 2.5 Ohm's of resistance requiring a min. of 22 AWG wire for the network. .......or...........

Go down to the hardware store and get a clamp on amp meter with multi function options to measure the resistance overall or individualy lol.

[Note} I am an expert at justanswer.com and not familiar with other formats of similar venues. I apologize if my addition to this answer was added out of protocol or if I "stepped on" someones session answer.

[*] (each entity of a circuit has it's own resistive value such as the wire, the heating element, and the devices used to control it which are all added together [Rt=R1 + R2 + R3 + etc....} to make the total resistance.

[**] {current is the amount of electrons that passes through any given point of a circuit for one {1} second known as a coloomb and is measured in "Joules".

Answer 2

An amp meter can be added in series with the circuit which is difficult in most circumstances of with a clamp on amp meter which is much simpler. A clamp on amp meter measures the magnetic field that surrounds the conductor and converts its strength into a current readout.

Answer 3

It depends on what information you are given to arrive at the amperage value. Three equations are I = E/R, I = W/E and I = sq. root of W/R. Values; I = amps, E = volts, W = watts, R = resistance.

Answer 4

Amps = volts / ohms.