Guide to the Markings on Electrical Switches

African American woman fixing light switch
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Switches are marked with different labels to identify ratings, types, and acceptable wire types. The UL label will also tell you if the device has been tested for safety by an independent testing agency, such as the Underwriters Laboratories. A switch will tell you if it's approved for alternating current (AC) applications only, the voltage rating, and the maximum allowable amperage.

The labels will tell you what the allowable wire connections are for the switch. If it reads, "use CU wire only", the only copper wire may be used for the connections, not aluminum. If it says, "CO/ALR", that means that either copper or aluminum wire installation is allowable. The manufacturer lists these labels to identify all of the previously mentioned labels. This will ensure proper installation of switches in your home.

Some switches are used for things like on/off switches on battery-operated devices like radios or to control things like fog lights on your car. These are DC switches and are rated differently than that used for AC applications in your home. 

Your home has a variety of switches that are used both alone and with a combination of other switches to control lighting, outlets, and devices like being a disconnecting means for furnaces and garbage disposers. One combination may be a set of three-way switches used to control the lighting in a hallway. Now add in a four-way switch or two to the mix and you can control the lighting from many more locations. These switches, along with single-pole switches, are primarily used in your home every day. 

In the homes of the future and the green homes, you are likely to find LED lighting and the possibility of solar panels powering the light switches. This lighting may be using 12- or 24-volt power for the entire lighting in the home. These specially marked switches are designed especially for the low voltage lighting. Check the rating on the switches to see the allowable wattage and do not overload the circuit.

Always take the time to look a switch over well and determine if it has a 15-amp rating or a 20-amp rating. The difference is obvious, but the strength of the contact points within the switch and thickness of the components, not to mention the quality of the switch, is a big difference. 

Switches are rated as either standard or commercial grade. You will soon learn that buying the cheapest switch will only cost you, in the long run, meaning you'll be changing out the switch again soon in the future. I believe in buying the better grade switches and avoiding the breakdown factor of cheaper switches. 

Electrical labeling on a wire's insulating jacket tells the story of the wires ruggedness. You'll likely see labels like THHN or THWN written on the wire. THHN wire stands for thermoplastic high heat-resistant nylon coated wire. THWN stands for thermoplastic heat- and moisture-resistant nylon coated wire.

The "T" stands for thermoplastic, the type of insulation covering the wire itself. The "H" stands for a heat resistance of up to 167°F. Likewise, the "HH" stands for a heat resistance, only it increases the rating to 194°F.

The "W" stands for moisture resistance. The "N" stands for an additional nylon coating that makes the wire both oil and gasoline resistant. As you can see, these wires are built to take on many different conditions.

The labeling on the wire also tells the conductor size and what the wire is made of, either aluminum or copper. 

As you can plainly see, labeling on electrical switches and wiring is important and is informative if you know what the lettering and symbols mean. By taking the time to examine these devices, you'll learn a lot about the electrical devices that you are using. Take your time and choose wisely for switches that will last a lifetime.