Episode 17 – How Circuit Breakers And Electrical Panels Work

A lot of green apprentice electricians ask about how panels work, and more specifically what the roll of the circuit breaker is.  Some guys think that breakers “put out” electricity, or that they “send” a certain amount of amperage to a load from the panel.  This is not how it works.

To start out, an electrical panel is simply a place where all of the many loads throughout the house meet up with the main feeders or service entrance conductors coming into the building.  It’s essentially a large junction box.  But rather than just joining all of the branch circuits and feeders to the service entrance wires, we put breakers in between each circuit to protect that circuit from any problems that may arise.

To understand how electricity flows we must understand the idea of “difference of potential.”  When a difference of potential energy exists between 2 wires, connecting those wires together will allow current to flow through them.  It will be extremely dangerous due to the amount of electrons flowing through the circuit, and you will most likely see an explosion happen in front of you.  So don’t do this.  Electricity is extremely dangerous in a circuit without a load or impedance in it.  So to make electricity useful, we have to introduce a load to the circuit.  A load is essentially a resistance.  It is something that slows current down.  Loads can also be inductive/capacitive and therefore reactive rather than resistive, but we won’t get into the semantics of this topic, in this post.  For now just understand that for electricity to be useful it must be slowed WAY down.

When a circuit has a proper resistance on it (say a toaster or lightbulb), the current slows down to a usable level and does not allow an explosion to happen.  But sometimes parts wear out and when this happens current can rise to dangerous levels (essentially speeding back up).  When this happens we want to have a protective device in place to disconnect the circuit so it doesn’t melt or cause a fire.  Enter the circuit breaker.  (By the way…fuses are very similar to breakers and serve the same function.  More on that in another episode)

A circuit breaker does not “output” any power.  It simply allows current to flow through it until that current gets to a dangerous level, in which case it automatically opens or “trips” the circuit.  A breaker is essentially an automatic switch.  It can be manually opened or closed (turned on or off), or it can automatically trip by sensing how much current is flowing through it.

Breakers “sense” current flow by a small electromagnet inside of the device.  For instance, a 40 amp breaker will have an electromagnet inside of it that when more than 40 amps flows through it, magnetically (mechanically) pulls the contacts apart – stopping current from continuing to flow through the device.
 

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**Disclaimer – These videos are for training purposes alone, all work done on electrical systems should be done by a licensed and insured electrical contractor.  If you are not an electrician, do not attempt any of the work you are seeing in these videos.**

Comments

John Boone says

Howdy Dustin,,,Gunny B here. Great videos! Clear and simple. Way to go brother.
I’m wiring a shop here in Mineola, Tx. I bought brand new 250′ roll of Orange 10/2 for $100 on craigslist and I already had a 250′ roll of yellow 12/2. Running half the shop with 20A outlets w/orange 10/2 split to two 30A breakers. The other half is 15A outlets w/yellow 12/2 to two 20A breakers. I’m following your guidance in video #3 for switches to lights. Question,,,do I need to run Orange 10/2 through the switch loop to light where I tie into 20A outlets, or can I tie into the 10/2 with 12/2 @ the switch boxes? Running low on 10/2, so hoping I can finish two light/switch loops with the 12/2? When finished wiring the shop, going to hire a licensed electrician to check my work and run from main at house to breaker box in shop.
Thanks again brother,,,you make this easy and save me a buttload of $’s ?

Dustin Stelzer says

Hey Gunny! You don’t need 10/2 unless you’re wiring a 30 amp circuit. 12/2 is good for the entirety of a 20a circuit.

Bree Toney says

Hey, Dustin! Do you have any best practices for deciding what all is included in one circuit? For example, is it a good practice to have overhead lighting on separate circuits from the receptacles in a room or rooms? Is it better to have every other receptacle in a kitchen (aside from large appliances) on alternating circuits? How do you go about deciding where to start wiring?

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