Each light string has a 15-foot extension cord with a male car accessory style plug, and the separate lit length of lights has proprietary low-current male and female end plugs.
Run up to 30 of these light strings in series. Each light string is packaged with an extension cord that has a male accessory plug on one end and a custom plug on the other.
They are both moisture and weather-resistant and can be used in both indoor and outdoor applications safely.