Breakdown of Volts, Amps, Resistance, and Power for Electricians

Breakdown of Voltage, Amps, Resistance and Power

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You will hear the terms Volts (Voltage), Amps (Amperage), Resistance (Ohms), and Power (Watts) A LOT in the electrical world.

When a circuit is formed, all four will have a value in a 100% purely resistive circuit. (We will briefly discuss Resistance vs. Reactance below, which will explain why 100% purely resistive matters in this sense).

IN THEORY knowing Volts, Amps and Resistance with Ohm’s Law are important to pass school, but in the real world, we electrician’s typically just READ THE NAMEPLATE of equipment, or view the equipment schedule to know wire size, voltage, etc.


What We Cover in this Article:

  • What is Voltage, Amperage, Resistance, and Power

Voltage Explanation:

The best way to think about Volts is how much pressure the circuit is providing.

Typically the higher the voltage, the smaller the wire size can be. This is because there’s more “force” or “potential” when the wires are connected.

You need two wires to make the circuit work.. whether that be a HOT and a NEUTRAL, or two separate phases, like for your oven which has two hot wires for 240V. But if you notice when you’re out there wiring a real range (oven and cook top), you run a #8/3NMD, which has a white wire for your neutral! That’s because even thought 240V supplies the heating elements to cook, we still need 120V for certain digital components and the lightbulb!

Voltage example: If the same motor is used.. if 120V, the wire size would be MUCH larger than if the motor was 600V. (Learn why we use higher than 120V).

Amperage (Current) Explanation:

Amperage is what actually travels within the wire when the circuit is complete.

Amps make the wire HOT, so you must understand wire size as an electrician, because if your wire is too small, it can cause a fire. But, that’s why we have circuit breakers, because they monitor how hot a wire gets, and will trip (break) the circuit to prevent the wire from overheating.

Other terms for Amps are “Current, Amperage, or Ampacity”.

Resistance (Ohms) Explanation:

Ohms Symbol for Resistance (Ohm's Law) - Becoming-an-Electrician.com
This is the Ohms Symbol for “Resistance” (Also known as the OMEGA Symbol).

Resistance is required for an electrical circuit to work.

If you connect the HOT and NEUTRAL wire together without resistance, you will get a huge flash before your eyes, which is called a “short-circuit”. This can be very dangerous to you, or damage the equipment (it can fry it 🔥💥!).

There is actually a minimum amount of resistance required in your circuit (minimum resistance threshold) in order for the circuit to work properly.. But when we plug in items purchased from the store (TV, Toaster, etc), these products have the proper resistance figured out for the circuit to work properly. (Usually, resistance isn’t on the nameplate, but Voltage, Amps, Watts, or Horse Power are, so you know wire size and how to properly connect the electrical device).

In a 100% purely resistive electrical circuit, we get WATTS (True Power), but when our circuit contains inductance, we get VOLT-AMPS (Apparent Power).. explained more below briefly.

Examples of a 100% purely resistive circuit are things like:

  • Baseboard heater
  • Basic toaster
  • Old incandescent lightbulbs

However, things like motors are not 100% purely resistive because of inductance, and so we use the word REACTANCE and IMPEDANCE instead of RESISTANCE! (It’s a little more complicated than that, but you must know to figure out your circuit.. or just read the nameplate 🙂)

Power (Watts) Explanation:

Power (WATTS) is what happens when we multiply Volts * Amps in a purely RESISTIVE circuit.

If your circuit contains inductance or capacitance (reactance), “WATTS” is actually called “VA (Volt-Amps)”, and has to be mathematically calculated with Pythagoras Theorem, compared to just Ohm’s Law.

Pythagorean-Theorem Example from Becoming-an-Electrician.com
Pythagorean Theorem is what you will learn in electrical school to understand about REACTANCE.

Understanding Electrical Math Formulas for School..

As mentioned, if you’re still an electrical apprentice in school, then knowing how to calculate these metrics like Volts and Amps is incredibly important.

But in the REAL WORLD as electricians, we rely on the ENGINEERS to calculate that for us.

We simply look at our electrical prints, equipment schedules, and nameplates to know how to size our wires properly.

I’d definitely recommend reading the different types of prints for electricians.

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