Often referred to as lamp wire or zip cord, this wire type is found in more than just Christmas lighting so it’s a question that is asked often. Unfortunately, there is a lot of conflicting information about SPT1 and SPT2 wire that tends to cause some confusion.
SPT stands for Stranded, Parallel, Thermoplastic and is used to describe most flat, 2-wire systems. The SPT abbreviation is always followed by a number that indicates the thickness of the insulation. The actual wire gauge (AWG) is the same across all of the SPT wire that we sell. It is an 18awg wire wrapped in either a .03" insulation (SPT1) or a .045" insulation (SPT2). The thickness of the insulation is the only difference between SPT1 and SPT2.
You will often read that SPT1 is rated at 7amps and SPT2 is rated at 10 amps. This is not true. The gauge of the wire is what indicates the amperage rating of the wire, not the insulation. All of our SPT1 and SPT2 wire is rated at 10 amps (18awg).
The only thing that will affect the amperage rating of an 18awg wire is voltage drop of distance. The longer the run, the lower the maximum load rating. Here's a quick guide:
0 to 50 feet: 10 amps
51 to 150 feet: 7 amps
151 feet or longer: 5 amps
In most cases, SPT1 wire will do the same job as SPT2 wire. There are two scenarios in which SPT2 could be beneficial. 1) you intend to use it in a display that will be up 365 days a year/permanent. In this case, the extra insulation will help prolong the life of the wire as it battles mother nature. 2) your display or use case is in an extremely cold environment. In this case, ice and cold can drastically affect the performance of the wire even with heavy due extension cords - having a little extra insulation will always help.
Whichever you choose, be sure to also use matching SPT1 or SPT2 plugs and accessories that properly fit your chosen wire.
