Are you installing a new breaker in your panel and need to know what size wire you will need?
In this guide, you will learn:
- How to size wire for a breaker!
- What breaker load capacities are
- How to read the cable markings
- And more!
When installing a new breaker or changing out a breaker, it is critical to ensure the right size wire is being installed with it.
Anytime I am working on a home remodel myself or helping a client I make sure to figure out what the main objective for the circuit is going to be. If it is just a new convenience circuit a 15- amp breaker with number 14, but if it is going to run something specific, I have to do some digging to get all the load information for that piece of equipment or appliance.
When deciding what size wire to use, first, you must make sure you have the correct size breaker! Once you know the size breaker you need, based off the amperage load, sizing the wire is pretty straight forward.Keep in mind this article is intended to be used as a guideline, if you have any questions or run into any problems, be sure to call your local electrician to come help. They will know all the national and local electrical codes that need to be followed. Electrical safety must be the top priority!
How To Size Wire For A Breaker?
The wire size will be determined by the breaker size and the amp load of the circuit.
Wire is sized by gauge, or the diameter of the wire. In electrical wiring it is referred to as AWG (American Wire Gauge).
The gauge of the wire determines how much electricity is capable of traveling through the wire. The smaller the wire gauge, the bigger the wire, and the more current it can safely carry.
The length of wire needs to be taken into consideration before beginning as well. If the length is over 100 feet, it is possible that you will need to upsize the wire by one size. This helps prevent voltage drop which is caused by the increase of resistance of the current traveling down the wire.
It is important to note these sizes are for copper wire. Please contact a local electrician if you are using aluminum wiring to get the proper sizes.
Wire Gauge And Circuit Breaker Sizing Table
How To Size The Circuit Breaker Amps?
When adding a circuit breaker, it must have a higher ampacity than the load it will be carrying.
To properly size a breaker, you need to know the total amperage load it will be carrying. If you are planning to put multiple outlets on the circuit that certain appliances will be plugged into on a normal basis, you need to add up the total amperage between all of them. If an appliance only lists the wattage, you can calculate the amperage by dividing the wattage by volts.
Breakers are supposed to be loaded to only 80% of their capacity. So, if you plan on installing a 15-amp breaker but, the total amperage is over 12 amps, you will need to up size to a 20-amp breaker and run 12 AWG wire.
If you are upgrading an appliance that requires less ampacity, you are allowed to just change the breaker and outlet to the correct size and leave the wire as is.
If the new appliance needs a larger ampacity, the breaker, the outlet, and the wire will have to get upgraded as well.
Common Household Appliances And Wire Sizes
15 Amp Wire Size
Most household outlets run on a 15-amp breaker. They have a maximum amperage of 12 amps and are run on 14 AWG wire. Lighting circuits are also run off this size circuit.
20 Amp Wire Size
The National Electrical Code requires a minimum of two 20-amp circuits in the kitchen. This is run with a 12 AWG wire and has a maximum of 16 amps. Many homeowners like to have one or more for outdoor or garage outlets.
30 Amp Wire Size
If you have a central air conditioner, it is most likely running on a 30-amp circuit. This requires a 10-AWG wire and no more than 24 amps can be put on the circuit. Another thing you may have a 30-amp circuit for is an RV power hook-up.
40 Amp Wire Size
Electric stoves and cook tops may require a 40-amp circuit; therefore you will need to run an 8 AWG wire for it.
50 Amp Wire Size
Some household appliances can require a 50-amp circuit. An electric dryer or electric water heater may require 50 amps of power and a 6-AWG circuit will need to be run.
When To Use 240-Volt Wire Sizes?
To be more energy efficient, 240-volt circuits are required for larger appliances when you start to get into the 30-, 40-, and 50-amp circuits. There are a multitude of household appliances that will use a 240-volt circuit.
- Electric Dryers
- Electric Water Heaters
- Electric Ranges
- HVAC Equipment
- Electric Vehicle Charging Station
240-volt circuits are more energy efficient because they require less current or amperage to provide the same amount of power or watts.
For example, you need 5,500 Watts:
5,500W/120V= 46 Amps
5,500W/240V= 23 Amps
You are able to cut your amp draw in half!
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What Are The Risks of Incorrect Wire Sizing?
If the wire is sized too small, it can create a dangerous hazard in your home.
Amperage causes heat, so undersized and inadequate wiring can heat up and cause the insulation to melt. This creates a major fire hazard. Anytime a wire heats up, it lowers the integrity of the breaker, the insulation, and the wire itself.
Appliances, devices, or anything plugged into a circuit with undersized wiring, will run the risk of being damaged.
Wiring being sized too big doesn't present any risks; it just adds unnecessary cost. It is also harder to handle because it is heavier and stiffer.
What Do The Markings on Wire Cables Mean?
Most home electrical projects the wire you need will come as a cable, and to make sure you are purchasing the proper cable for your application it is best to understand what all those marking mean.
The gauge of the wire will be listed as an AWG, so for a 14-gauge wire it will read 14AWG.
The next number will tell you the number of current-carrying conductors in the cable. For example, 14-2 or 14/2. This means there are 2 current-carrying conductors.
Some cables come marked with a "G" or "w/G" this means there is a ground wire along with the previously listed number of current-carrying conductors inside the cable.
If you want more details on wire markings, we recommend this helpful guide by theSpruce.com.
Frequently Asked Questions
How Do I Know What Size Wire and Breaker I Need?
You need to know the total amp draw that will be on the circuit. Then you will size the wire and breaker based off that, keeping in mind you can only load a breaker to 80% of its capacity.
What Is The Standard Size Of Wire For Circuit Breaker?
The most common sizes used in a household application are: 14 AWG, 12 AWG, 10 AWG, and 8 AWG. These are based on the size of the breaker and amp load of the circuit.
What Size Wire Will Fit In A 50-Amp Breaker?
The minimum wire size required for a 50-amp breaker is a #6 AWG.
How Far Can You Run 10/2 Wire On A 30-Amp Breaker?
The maximum length of 10/2 on a 30-amp breaker is 150 feet before you will begin to experience voltage drop.
Final Thoughts On Wire Gauges
Sizing wire is a critical step in the installation process. Factors that must be considered when sizing a breaker and wire, is the amount of ampacity needed and the length of the wire run. To keep your home and family safe NEVER undersize the wire needed.
Be sure to contact a local electrician for help making sure you have everything size properly. They will help guide you through the local and national electrical codes to make sure the wiring is up to par.
I hope you enjoyed this Home Inspector Secrets guide!
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