15 amps wire size - All you need to know

What size wire for 15 amps?

To safely use a maximum current of 15 amps, you will need a wire gauge of 14. A 12 gauge wire is a safer bet, but a 14 gauge wire will work just fine. 15 amp wire 14awg

To know for sure what kind of wire you should use, refer to your breaker box and see what size wires are already run from the main panel to your house or service panel. If they're 12 gauge, then you're good to go with an extension cord made for 15 amps. If they're not 12 gauge, find out how many amps that circuit uses and buy a larger wire.

A 15 amp receptacle can sometimes be used with a 20-amp circuit. However, the 20-amp circuit will carry 15 amps but the extra 5 amps are not safely carried and so the increased power dissipation in the line must be taken into account.

15-amp vs. 20-amp

Most of the circuits in a residential home uses 15-amps. In other words, most circuits run on 15-amp breakers. However, you can run a 20-amp circuit if the wire size is correct. Since 20 amps generates twice as much heat as a 15-amp circuit (not to mention that longer runs will require thicker cables), it's usually not safe to do so unless the cable is at least three times bigger than what would be required for a 15 amp circuit (which translates into 3/0 AWG). And since larger wires cost more money, you have to ask yourself whether or not it's worth spending extra cash just to save time on installation.

A 15-amp circuit requires a 14AWG wire while a 20-amp circuit needs 12AWG wire. When in doubt, check your local building code to see what the minimum is. However, keep this in mind: Using a 20-amp breaker on 14 AWG cable or smaller will cause problems and might even lead to a fire.

What is "gauge" or AWG?

Gauge (AWG) refers to the thickness of an electrical cable. The larger the gauge number (such as 10 vs 12), the thinner the wire, which makes it lighter and more flexible but limits how much power can pass through at any one time. For example, smaller cables have thinner wires inside them that are able to handle less amperage than those with thicker wires.

As stated above, the wire that has the larger number is much thinner than a wire with a lower number. A 10AWG wire is larger than a 12AWG wire.

The range for gauges from smallest to largest are as follows:
  • 20-16 - used in automobiles and other similar applications where battery cables or fuses carry a lot of current.
  • 14-12 - used in household wiring , often for AC (alternating current) outlets, switches, light fixtures, extension cords etc. Note: this is the most common household wire size used today.
  • 11-8 - light duty appliances such as computers and small electronic equipment such as clothes dryers, dishwashers, air conditioners etc. This is also referred to as "gauge B".
  • 6-4 - medium duty appliances such as freezers, stoves, hot water heaters and washing machines. This is also referred to as "gauge A".

12-Gauge Vs 14-Gauge Wire

The main difference between these two types of wires is the thickness of each wire. In general, 14-guage wires are thinner than 12-gauge wires and for this reason are used for carrying less current. This means that they can handle less electrical power/amperage (amps). For example if you had two appliances such as a washer and dryer, both may use 15 amps however, you really want to try not to run them on the same circuit (the load exceeds 15 amps) unless you have #12 AWG wire (2.5mm²). The problem is 2.5 meters of #14 AWG carries only 13 amps and a few feet more can make all the difference, especially when there is more distance between the panel and appliance outlet.

What is an amp?

An amp is defined as the rate of flow of electricity through a conductor when the potential difference between its ends is one volt. To put it another way, an amp is a measure of how much electric charge flows past a given point in an electric circuit each second.

What is voltage drop?

Voltage drop is the difference between the voltage measured at the line and the voltage measured at the device.

It's usually caused by a mismatch of cable gauge (thickness) and current flow. In other words: The thicker the wire, the less electric current can flow through it. A thick wire with much current passing through won't be able to carry as much power as a thin wire. Voltage drop occurs when there is too much resistance in your circuit because of using larger-gauge wires than you need for your application.

The same amount of electricity will move along any given conductor only more slowly if its resistance is higher, an effect directly proportional to length and inversely proportional to sectional area or diameter. Resistance also increases proportionally with temperature rise and inversely with length of run. Since extra voltage drops are created in longer wires by internal resistance, the power lost due to this effect.

What is more important than voltage drop in electric circuits?

Something that is more important than voltage drop in an electric circuit is current losses. Voltage drop only affects the power factor, not cause a significant amount of energy loss in a system (enough to make a difference to the user). Most people are most interested in getting as much out of their circuits as possible, not in making them "efficient."

Most Electricity 101 handouts will tell you that when using large wires for high current applications that you should use larger-gauge wires than needed because of voltage drop. This is true if looking at it from one point of view, but it may be less true if considered another way. This other way is to consider the energy in/out of the wire.

If your system is a low-voltage DC (such as 12V) system which has voltage drop, you should use larger wires to avoid voltage drop and keep maximum power going into and coming out of the circuit. This is true because while you do lose some power to resistance, if you increase your wire size to 1/2", you will lose only about 0.1% of the power going in, and about 0.5% of the power coming out compared to using smaller wires because the voltage drop will be proportional to resistance (more current => more resistance, but voltage is constant).

15 amp breaker wire size

A 15 amp breaker requires wire size of 12 gauge. If it is a 10 amp circuit, then the wire requires 14 gauge. This is because the house wiring in your home has very little resistance built into it (from 20 years ago when wires were smaller). So, the breaker will only be operating at maybe 2 amps or so and won't have to worry too much about voltage drop from resistance with that small amount of current passing through such large wire sizes compared to an individual 12V system which might be running 100 amps on high power.

What is an electrical box?

An electrical box is a box that provides a structure for the circuit breaker and an enclosure to protect it. In some cases, where you're working with metal boxes, they can also act as a grounding point.

Use an Enclosure or Not?

The answer should usually be yes. An enclosure will protect the circuit breaker and help ensure that it works long-term. If you're working with an electrical box that's not designed to be an enclosure, there are still some ways to effectively use one:

Use the Box as You Would a Metal Enclosure

Most metal boxes will usually have tabs on the back side so that you can mount them directly to another surface like drywall or wood studs. However, if you don't want to mount them directly to your wall, there is another option:

Mounting Brackets

These brackets will give you a way to mount your electrical box in the desired area. Before we get into how, let's talk about why.

Use Metal Boxes for Outdoor Wiring If you plan on using your wiring outdoors, this is especially important: PVC and plastic boxes are designed for indoor use only , so they aren't rated for outside conditions . When used outdoors, they can deteriorate prematurely and can even cause a fire hazard because of the potential for water damage.

The Easiest Way to Use an Enclosure With an enclosed circuit breaker panel or metal enclosure, there are two easy solutions on the market which work very well together:


3% Max Voltage Drop, 120 Volt, Conductor size (AWG)
Single Phase (Copper)
Distance of Run
25'50'100'150'200'Amperage
Copper3/03/03/0300 MCM500 MCM200 AMP
Copper1112/04/0100 AMP
Copper101064430 AMP
Copper1412108615 AMP
Copper121286420 AMP
Conclusion

This article has gone over all you need to know about the wire size needed for 15 amps. The main thing to remember is that different wire sizes have different ampacities, and you'll need to know whether or not it's OK for your project. If in doubt, play it safe and go with a larger size wire. I hope you found this article useful. Feel free to bookmark it, and check out some of my other articles.


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