When you are looking online at Christmas light stringer wire have you ever noticed the SPT designation? It’s merely an indicator of the thickness and durability of the insulation. Most of the time, it may not be even listed as a specification. If it’s not, you can almost always assume (but you know what they say about people who assume…) that it is SPT-1.
There is another alternative now becoming more readily available online – SPT-2 rated insulation. It has a slightly thicker insulation than SPT-1 and we’ve decided that demand finally justifies carrying it so Christmas Light Source will start carry all of our C9 and C7 stringer wire in SPT-1 and SPT-2 insulation thicknesses.
In non-Christmas light applications, SPT-1 is used for everyday lighter-duty applications. SPT-2 cord is commonly used for larger appliances like refrigerators.
The current rating of the wire or cord you are considering is based on the gauge of the wire – not the SPT rating. Most of the pre-made Christmas light wire is 18 AWG (or 18 gauge) and is rated at 10 amps.
There is some misinformation on the internet that a higher SPT rating would indicate that the wire can take a higher current – this argument is used to say that SPT-1 can’t carry the same 10 A as the SPT-2 version. This is not accurate information. The amount of current a cable or wire is rated for is strictly a function of the copper used for that cord.
Please remember with all things electrical that if you have a serious question about what wire to choose and how it will work in your situation that a Master Electrician is the first person to consult with – and I suggest that you consult with one on any project where you are cutting 1000 foot spools to custom lengths – especially at commercial installations.
For most applications, where lights are up 2-3 months a year, in most environmental conditions SPT-1 is perfectly suitable and since it is a hardy cable at the most reasonable price is generally the most popular choice of installers, as a rule of thumb.
SPT-2 is best used where environmental conditions are more extreme or a longer term installation is desired – keeping in mind that most companies provide a 90 day seasonal warranty on lighting products no matter what the configuration or specification. This is the UL recommended guideline because customer environmental conditions vary so widely.
So, the ultimate decision to use SPT-1 or SPT-2 will be a factor of your project, environment and budget.
Oh, and as a tip, make sure that the plugs you purchase are rated for either SPT-1 or SPT-2 as the second variety has to be designed to fit the larger insulation.