SPT-1 Wire and SPT-2 Wire: What's the Difference?

For those of who don't know what SPT-1 wire is - it is also known as lamp wire or zip cord, and is commonly used by decorators to build custom lengths of extension cords. It allows for a clean display installation by elimination excess extension cords that can be unsightly. So what are the differences? For some reason this has become a somewhat confusing topic, but really, it's quite simple: They are exactly the same with the exception of the thickness of the insulation covering the wire. Both SPT-1 wire and SPT-2 wire are made using 18 gauge copper wire at their core. The difference is that SPT2 has a thicker insulation around the wire. Thereby making it slightly larger around than SPT1 and giving it the ability to carry a slightly higher electrical load.

Some folks will say that an SPT1 18awg wire is rated to carry a 7amp load and an SPT2 18awg wire is rated to carry a 10am load. While this is true under certain conditions, there are other variables that also affect the safe use of any wire type - including the length of the run (voltage drop over distance), the thickness of the insulation, the quality of the copper wire, etc. We always recommend that you seek the services of a licensed electrician if you have any question at all about the safety of your installation.

Visit The Christmas Light Emporium at the links you see here to learn more about all of the installation accessories we offer including a variety of colors and lengths of SPT wire and other professional installation accessories: SPT-1 and SPT-2 Wire Installation Accessories Happy Decorating!

Comments (2)

JP Mathieu

Thank you for the description of the 2 SPT wires. I understand that their only difference is the thickness of the insulation. But while an 18 Gauge 50 ft cord is set to carry 10 A, the 18 Gauge 100 ft is limited to 7 A . These are the same cords, one is twice as long as the other.
To say that because one wire is thicker than another (SPT-2 vs SPT-1) it can carry heavier load, this is a deviated explanation for the jump from 10 A to 7 A. The length of the cord is the changing factor, not the thickness of the insulation around the cord.
Your readers may loose confidence in your expertise after reading such statement and switch to other websites, just saying…
Thank you for reading

Darren Vader

Hi JP – you are absolutely correct. Any discussion about wire and its properties can be far more complex than what we present in the video above. Sometimes we try to keep things simple so that it is easier for folks to understand. We have some expectations (which are noted in our terms of service) that folks who are buying these types of products already know how to use them and that there is always a possibility of a dangerous situation arising if they do not.

I do think that your point (especially re: voltage drop) is simple enough to understand and explain that we have edited the text in this post to add some additional explanation re: thickness of insulation is not that only variable that needs to be paid attention to during project planning.

Thank you for taking the time to point this out – it has made the information more valuable to others! Take care!

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