Electrical overloads can become a problem. Do not string together more than three sets of 100 miniature lights. Do not mix miniatures with larger bulbs on the same string. The mismatched wattage could burn out bulbs or short a circuit. Do not overextend the circuit wattage capacity when setting out your outdoor lights.
Wattage is determined by multiplying voltage by circuit amperage.
This breaker shuts down the power supply the instant electricity escapes the circuit. The shut down occurs faster than one can become electrocuted. Do not use indoor extension cords outside. Another good suggestion for outdoor lighting systems is to wrap all connections in electrical tape. This keeps out moisture and prevents them from becoming unplugged.