18 gauge, 7 amp X-Wire has its limitations when creating extension cords or whips. Most Christmas Light products are listed in wattage so you will have to do some simple calculations to determine your limitations. Here's how; 7 amps x 120 Volts=840 watts.
Therefore, 840 watts is the absolute max power we can run through 7 amp X-wire. It is wise not to push the limit, so we like to use the 80% rule when working with power and lights. In this case, our limit would be 672 watts.
Each product you use will typically have the wattage listed. Here are a few of the more popular products;
Sparkle C9 LED Replacement Bulb-.58 watts
LED Mini Lights-Warm White 4" Spacing 70 Lights-4.8 watts
Using the above specs at 80%, we can safely run 672 watts of power through our X-wire. That means we can do 1,158 Sparkle C9 LED Replacement Bulb or 140 LED Mini Lights-Warm White 4" Spacing 70 Lights
Another factor you need to keep in mind is the length of your run. The longer the run of wire, the more resistance, and thus, more heat. Here are some examples;
Extension Cord Length (Feet)-25'
Extension Cord Length (Feet)-50'
As you can see, when you jump from a 25' cord to a 50' cord, your capabilities drop in half. This is important to keep in mind when running your power.