Allied Encyclopedia – What are the differences between SPT-1, SPT-2, and SPT-3 wire?

Allied EncyclopediaWith the holidays fast approaching and Christmas lights going up, SPT Wire is a hot topic. Its use in lighting makes SPT wire especially popular this time of year, but knowledge of SPT-1 wire, SPT-2 wire, and SPT-3 wire is useful for much more than Christmas decorations. SPT wire is used in a multitude of applications, including lamps, small household appliances, and other light duty applications. Knowing the differences between the three different types of SPT cable can help you determine which product is right for you.

The main difference between SPT-1, SPT-2, and SPT-3 is the thickness of the insulation that surrounds the copper wires, with each SPT wire having a thicker insulation than the previous. Generally, a cable with a thicker insulation will also have a higher maximum amp rating.

SPT cables feature stranded copper conductors and polyvinylchloride (PVC) insulation, and resist oil, water, acid, alkali, and ozone. All three types of cable are rated up to 300 volts and 60°C or 105°C.

SPT-1 Wire is the most popular SPT cord. SPT-1 has an insulation thickness of .030”. Because it has the thinnest insulation of the SPT wires, it also has the lowest amperage.

SPT-2 Wire features a thicker insulation than SPT-1 Wire at .045” thick. As a result, SPT-2 also has a higher maximum amp rating, and is able to handle more power.

Because of its thicker insulation, SPT-2 cord is often recommended for lower temperatures where the insulation may get brittle and crack. However, the thinner insulation on SPT-1 wire tends to be more pliable, so some professional installers believe that SPT-1 is actually better for cold weather.

SPT-3 Wire is the newest type of SPT cable, and it also has the heaviest construction. While SPT-3’s insulation ranges from 0.060” to 0.110” thick, its maximum amp rating does not greatly vary from SPT-2 wire’s amperage.

When choosing between SPT-1, SPT-2, and SPT-3 cord, be sure to consider insulation thickness and amp ratings. Ultimately, your choice of SPT wire will depend on your application.

Visit Allied Wire online for full SPT Wire specs or to purchase SPT Cable.

About awcwire
Allied Wire & Cable is a value-added manufacturer and distributor of electrical wire and cable, tubing, and more. We are a family owned and operated company, serving a wide range of industries, including the military, automotive, aerospace, and telecommunications markets. Allied is headquartered in Collegeville, PA. Additional locations can be found across the US, in Phoenix, AZ; Bedford, NH; Pewaukee, WI; Rochester, NY, Tampa, FL; and Mt. Juliet, TN. For more information on Allied, visit our main website at

3 Responses to Allied Encyclopedia – What are the differences between SPT-1, SPT-2, and SPT-3 wire?

  1. Eddie Graber says:

    Why no mention of UL -r standard, SPT-2 lamp cord standard?

  2. Ken Knowles says:

    Wouldn’t thinner insulation have a higher amp rating? It would dissipate more heat. Thicker insulation would give a higher voltage capacity.

    • awcwire says:

      We apologize for the misleading wording! By definition, ampacity – also known as current carrying capacity – is the maximum amount of electrical current the insulated conductor can safely carry without exceeding its insulation and jacketing limitations – either surpassing temperature ratings and/or causing the wire to degrade.

      Typically, the heat resulting from the voltage drop and power dissipation would cause the insulation to degrade long before the metal conductor would be damaged, so the properties of the insulation are important considerations in determining ampacity. In short, the ampacity of the wire depends on the physical and electrical characteristics of both the conductor and the insulation. I hope this helps to clarify! And thanks for reading through our blog!

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