Understanding the Difference Between SPT-1 and SPT-2 Cord

We frequently get questions regarding the difference between SPT-1 and SPT-2 cord. There is a lot of confusion and even long time professionals don’t fully understand the difference and what makes one better than the other. You’ll also find incorrect listings all over the Internet stating that SPT-2 cord can carry more amperage. This is not accurate information. The only difference between SPT-1 and SPT-2 is the insulation. Contrary to popular belief, thicker insulation does not translate into being able to carry a higher load. Before going any further and explaining when one type of cord should be used over the other, here’s the simple answer as to what the difference is between the two ratings:

SPT-1 – Standard Insulation – .03″ (16 and 18 gauge) – Max Load 7 Amps

SPT-2 Thicker Insulation – .045″ (16 and 18 gauge) – Max Load 7 Amps

When installing Christmas lights and decorations, zip cord and light line are often used. These are usually made from 18/2 wire. However from time to time 16/2 cord may also be used and in some cases a very thick 14/2. But since most Christmas lighting and decorating projects utilize 18/2, we’ll focus on that for now. When looking at the two numbers for the zip cord, 18/2, the 18 refers to the size of the wire, which in this case is 18 gauge. The 2 means there are two wires that make up the cord. The smaller the number, the thicker the wire. So a 16 gauge cord is thicker than a 18 gauge.

As far as the SPT rating, this is simply the thickness of the insulation that surrounds the copper wires. 18/2, SPT-1 wire has an insulation thickness of .030″ and 18/2, SPT-2 has insulation that is .045″ thick.

Because SPT-2 has more insulation, it is often recommended for cold conditions where the insulation tends to get brittle and crack. However, in our own testing as well as feedback from other pro installers, we have not found any significant improvement in cold conditions. Even in the frigid Alaskan winters, we’ve had customers using SPT-1 without any issues.

The only situations we find that SPT-2 is necessary is when the cord will be out during the summer months. UV is the #1 enemy of lights and electrical cord and by having insulation that is twice as thick, you’ll get more life out of the cord. This is especially true for rooftop lighting applications where there is no shade and the UV index can hit above a level 10 during the summer.

Like many issues within the Christmas lighting industry, this is a topic of much debate and everyone seems to have their own opinion regarding which option is better. However, SPT-1 is still the most often used type of cord and we sell it about 10 to 1 over SPT-2. We’ve been installing Christmas lights for over 35 years in sunny, hot South Florida and we still use SPT-1 on all our seasonal installations. But from time to time when we’ll be leaving a project lit for a longer period of time, we will go ahead and spend a little extra and go with SPT-2.

Whichever option you go with, we’ve got you covered. Aren’t sure which cord is best. Give us a call or shoot us an email and we can help you out.

If you’re looking to shop our website for light line, zip cord or plugs, be sure and browse through the links below:

Bulk Light Line – SPT-1 and SPT-2 Zip Cord

Empty Socket Light Line

Comments

  1. Sarah says

    Than you so much for this info! This is the most to the point, easy explanation. Worded so nicely, It seemed like a kind hearted, dear old friend was explaining. Sincerely, Sarah.

  2. jonathan cirrero says

    I worked on the standards body of IEEE in the 80s and we worked very closely with UL on fire safety issues, all which led to alot of changes in the NEC codebooks. The SPT-X standards are really about application and was designed to account for different types of threat models and the overall vulnerability surface of exposed wiring. For example a higher gauge cable is recommended for apparatus which hangs, however a smaller gauge wire is needed for practical reasons on fixed apparatus such as sconces. Also in my 40 years of working with electrical infrastructure my #1 enemy to declare is not UV but mice. Mice love chewing on electrical wires, they are a pain in the ass.

  3. Ann says

    I’m trying to make a lamp that will hang on the wall for reading in the bedroom and would like to know if it matters which SPT I use for a lamp using a 60 watt bulb. I have already found that the iron scroll body I want to use for the lamp needs wire that is a little smaller around than the standard lamp cord in order for it to fit through. Thank you.

  4. Dom Gagliardi says

    Do you know anything about SPT-2w wire? Fire inspector came by and said spt-2 is not rated for outside but I need stringers with spt-2w. I feel like he is mistaken as I can’t find anywhere to even buy stringers with spt-2w. Appreiate you help.

    • Jason Woodward says

      Hi Dom, yes, you have run into a problem that is nearly impossible to overcome. We don’t run into this issue very often, but it does occasionally come up. SPT-2w is not very common and can be difficult to find, even in just bulk wire. Unfortunately there are no stringer sets made with this type of wire.

      Stringer style light sets are UL rated for 90 day or less usage, so if you are looking to go beyond this, some fire inspectors may take notice and ask you to remove them. However, if you are using the lights just for the holiday season and you are using proper extension cords, then you should be within code. If you want to discuss this in more depth, please give us a call at 800-391-5280 and ask for Jason.

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