Looking to use a lamp cord in an electrical project? Then you probably need to make a choice between SPT-1 and SPT-2. The main difference between those two cables is that SPT-1 has insulation 0.03" thick, while the insulation of SPT-2 is 0.045" thick. This is the only difference that matters. Despite the common stereotype, the ampacity of these two cables is not different and is 10 Amp at 18 AWG. Read this blog for more details about SPT-1 vs. SPT-2 and lamp cords in general.

What is an SPT Wire?

SPT is a Service Parallel Thermoplastic cable, also known as a lamp cord and zip cord (the term "zip cord" stems from the parallel configuration, meaning it is easy to zip two conductors apart). It is also known as Christmas lights or cable because it is recognized as a cable for outdoor and indoor holiday light installations used with Christmas light strings, such as C7 or C9 LED. SPT is a light-duty cord with a parallel design, copper conductor, and thermoplastic insulation, usually the most basic PVC. The voltage rating of this cable is 300V.

 The cable is resistant to UV, water, and weather and moderately resistant to oil, acids, alkalies, heat, and flames.

Applications of SPT Wires

The most common application of SPT wire is decorative indoor and outdoor LED lights that people typically wear for holidays like Halloween and Christmas. However, SPT is also a small appliance wire that is used beyond just LED lights. These are some of the other common applications of this cable:

• Lamps and lighting (includes all sorts of things, such as table lamps, floor lamps, desk lamps).
• Small household appliances that need less than 10 Amps (such as humidifiers, small fans, or clock radios).
• Small kitchen appliances (toasters, coffee makers, and blenders less than 10 Amps).
• Audio equipment: Lamp cords can be used for some speakers and radios instead of the speaker wire.
• As a light-duty extension cord for indoor use. You can read more about the applications of lamp cords as an extension cord here.
• Low-voltage DIY electrical projects. SPT wires are easy to work with, which makes them perfect for small-scale, low-voltage DIY projects.

SPT-1 vs. SPT-2: Points To Consider

Let's look into more detail about the differences between these two cables and when it actually matters if you choose one or the other:

• The insulation of SPT-1 has 0.03" thickness, and the insulation of SPT-2 has 0.045" thickness.
• Because of the thickness of the insulation, SPT-1 is cheaper than SPT-2, which, in many electrical projects, is the only difference that matters.

Both cables have a gauge of 18 AWG and are generally ranked for 10 Amps. The statement that SPT-1 is ranked for 7 Amps and SPT-2 is ranked for 10 Amps is false. As both of these are rated 18 AWG, the number of amps they can handle depends only on the expected run of these cables. Here is how many amps can both SPT-1 and SPT-2 handle based on the run:

0 to 50 Feet - 10 Amps 

51 to 150 Feet - 7 Amps

Over 150 Feet - 5 Amps

These stats do not change based on whether you use SPT-1 or SPT-2.

So, when does it actually matter if you choose SPT-1 or SPT-2?

SPT-2 performs considerably better than SPT-1 in cold temperatures in winter. If you plan to hang holiday lights outdoors in cold, snowy climates like Minnesota or Michigan, it is best to use SPT-2, as it will not crack and will be more durable. You can also use SPT-2 if the cable is exposed to more wear and tear than usual, but lamp cords generally should not be treated harshly. For all other occasions, it does not really matter whether you use SPT-1 or SPT-2. 

Can you use SPT-2 plugs on SPT-1 wire?

You can theoretically use SPT-2 plugs for SPT-1 wire, but it is not recommended, as SPT-2 plugs are designed for cables with thicker insulation, so the fit might not be as secure as desired. It is best to buy SPT-1 plugs for SPT-2 wires.