A few days ago, a reader asked me an electrical wiring question. He had a question I can imagine many homeowners might have prior to doing their homework about electricity or consulting an electrician.

This reader wanted to know if he could mix and match different wire sizes on the same circuit. Wires inside your home’s electrical cables come in different sizes, much like shoes or T-shirts. The short answer: No.

The longer answer requires some explaining. A wire’s size is referred to as the wire gauge. The most common wire gauges used in U.S. residential buildings are 14, 12 and 10. Sizing can be confusing because as the number gets smaller, the wire’s diameter gets bigger.

The wire size, along with the insulation that covers bare wire, has been tested and capacity rated by the National Fire Protection Agency (NFPA). For example, 14-gauge wire is rated for 15 amps or 1800 watts in the U.S. The 12-gauge wire is rated for 20 amps or 2400 watts. The wire powering your electric clothes dryer is almost always a 10-gauge wire. An electric dryer runs with 240 volts whereas most other home appliances run on 120 volts.

If you go to your electric panel, you’ll see a series of levers known as circuit breakers. Each breaker resembles a wall switch you use to control a ceiling light. Breakers are rated by amps, and you can see an amp number on each breaker. Look at yours: You’ll see lots of 15s and 20s.

Most of the breakers in your panel will be single-pole breakers, meaning a single wire is connected to the base of the breaker. In a normal circuit in your home, this wire leaves the panel and starts to daisy-chain to wall outlets and possibly a few lights. If the breaker is rated for 20 amps, then the wires on that circuit should be 12 gauge. You’d never ever want a piece of wire in that 20-amp circuit to be 14-gauge wire.

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Here’s why: Normal circuit breakers are designed to protect the wires and cables in your house. The breaker is designed to automatically shut off, or trip, if it senses excess electricity flowing through the breaker. The more electricity, the greater the heat build-up along the wire. If you put too much electricity through a wire, it can get so hot that it will melt the plastic insulation covering the metal wire and ignite it!

According to the NFPA, hundreds of people die each year in the U.S from electrical fires and thousands are injured. Electrical fires cause more than $1 billion in direct property damage in any given year.

The NFPA was essentially created by the insurance industry, which realized that consumers needed education about fire prevention. As electricity became available in homes, insurers realized they needed to make sure consumers understood electric wires and cables to stay safe and minimize fire risk. The National Electrical Code was drafted as a result of these efforts, and is a time-tested document outlining minimum standards for electrical installation in homes, businesses and other buildings.

If a circuit breaker in your home is constantly tripping, it’s screaming to you that something is wrong. You could be drawing too much current. Perhaps you are misusing extension cords. Call an electrician to diagnose what’s happening before you or your loved ones become statistics.

Even if your circuit breaker isn’t tripping, visit the NFPA’s website at npfa.org and immerse yourself in its educational materials. Learn how the invisible electricity in your home works. It’s well worth the time — and it will keep you safe.

Tim Carter has worked as a home improvement professional for more than 30 years. To submit a question or to learn more, visit AsktheBuilder.com.