The most frequently asked question that we always get is: What is the biggest difference between SPT-1 and SPT-2 wire?

The only physical difference between SPT-1 and SPT-2 wire is the thickness of the insulation:

• SPT-1: 0.03 inches of insulation
• SPT-2: 0.045 inches of insulation

That’s it.

Despite common misconceptions, the insulation thickness does not impact how much electrical current (amperage) the wire can handle. The amperage rating is determined by the amount of copper in the wire and the length of the cord, not the thickness of the insulation.

Pro Tip:

Never mix SPT-1 and SPT-2 components (such as plugs and wire). They are not interchangeable.
SPT-1 plugs are designed specifically to pierce through thinner insulation, while SPT-2 plugs are built for the thicker insulation of SPT-2 wire. Using the wrong combination can prevent the plug prongs from making proper contact with the copper wire, creating a loose or incomplete electrical connection, which significantly increases the risk of shorts, failures, or even fire hazards.

This is especially important for professional installers working with thousands of feet of cord and hundreds (or thousands) of plugs each season. Keeping your SPT types consistent across your inventory helps ensure both safety and efficiency during installation.

Common Misconceptions

Let’s address a few common myths:

1. SPT-2 Supports More Amps – ❌ False

Although many sources claim SPT-2 can handle more amps than SPT-1, this is inaccurate. For example, both 18-gauge SPT-1 and SPT-2 wires carry the same amount of copper, so they support the same amperage based on cord length.

*Never run more than 250 feet of 18-gauge wire, especially with C7 or C9 socket light lines. This can cause excessive voltage drop and overheating, posing a fire hazard.

2. SPT-1 Doesn’t Hold Up in Harsh Weather – ❌ Mostly False

SPT-1 performs very well in most environments, from tropical climates to freezing northern areas. Remember: most light strings use thinner 22-gauge wire and still perform reliably.

However, SPT-2 is recommended in:

• Longer-term installations (over 90 days): SPT-2 holds up better when exposed to long term UV light. 
  Please note: According to the National Electrical Code (NEC), 18-gauge wire should only be used for seasonal lighting (90 days or less).

• Extreme weather climates 

3. SPT-2 Is Always Better Because It’s Thicker – ❌ Not Necessarily

Thicker doesn’t always mean better. It depends on your installation needs, budget, and environment. For most regular installations, SPT-1 can be used without any issues.

Our Recommendation

For most customers, especially seasonal users, SPT-1 is the best choice. It’s affordable, reliable, and widely available. In fact, about 75% of what we sell and use ourselves is SPT-1.

Whichever you choose, just be consistent with your plugs and accessories, and you’ll be good to go!

Still Have Questions?
Read our full blog post here: What is the difference between SPT-1 and SPT-2 wire?

Our customer support team is also here to help. Reach out to us anytime for expert advice on choosing the right wire for your project.