What is voltage? This is certainly an important term to know in the electrical field. You hear it all the time. What is the voltage on the machine? Or, can you check the voltage on that circuit? We hear it, we say it but, what is voltage and how does it relate to metering?
What is voltage?
The most commonly used voltage definition states that voltage is the difference in potential between two points in a circuit. What a definition of voltage right? Another way that voltage is defined is by talking about water. Some find it easier to understand the voltage definition when we talk in terms of water pipes. Voltage is the driving force in an electrical circuit. We can think of it as the pressure in the circuit. So, what is voltage? It is the driving force in an electrical circuit.
How is voltage measured?
Voltage is measured using a voltmeter. With a voltmeter we can choose two different points in the circuit to measure the difference in potential across those two points. The unit of measure for voltage is known as the volt. The volt is named after Alessandro Volta who created the first battery known as a voltaic pile.
How does voltage relate to metering?
Ah yes, the big question is, how do we use voltage in metering? Well, we have to remember that meters measure kilowatts. So, what does that have to do with voltage? To find the kilowatts, we first need to find the watts. To calculate watts we need to know the current and the, you guessed it, voltage. Using Ohm’s Law we know that power is equal to voltage times current or stated mathematically, P = I x E. There are several ways you can remember this formula. One is by remembering the word PIE. Another is to change the letters to W = V x A.
In the first example, P = power measured in watts, I = current measured in amps, and E = voltage measured in volts. Just a quick fact here, E is the letter used because it stands for electromotive force which is a fancy way to say voltage.
In the second example, W = watts, V = voltage, A = amps. So, the two equations are equal they are just using different terms. The easy way to remember W = V x A is to think of West Virginia or W VA. Pretty simple right.
So, now that we know the terms we need to know how they relate to metering. Well, the nominal voltage in a typical metering circuit remains pretty much constant. A common household voltage is 120/240. So, the meter measures this voltage and then multiplies the voltage times the current in the circuit to get watts. And then as if by magic the readout is in kilowatts.
What?
Look at the equations again and go back to algebra I. If the voltage stays constant and the amperage goes up that means that the wattage will go up. If the amperage goes down, the wattage goes down. To get kilowatts from watts, divide the watts by 1000. In the older electromechanical meters the voltage coil, also known as potential coil, produced a magnetic field in the meter. When current flows through the meter it produces a magnetic field as well. The interaction between these two fields are what causes the disc to turn. So this is why it is important to make sure that the meter chosen for each installation is crucial.
Conclusion
Voltage is the driving force behind each and every electrical circuit. We can use Ohm’s law to calculate watts using the power formula. It is the interaction of voltage and current in a circuit that causes the meter disc to spin. To check the voltage in a circuit we use what is called a voltmeter.