You cannot mix too many thick wires in a small box. The National Electrical Code (NEC) sets the standards for safety. This enclosure houses the circuit breakers and bus bars that manage and protect all the electrical circuits running throughout the. Power conductors rated 1,000V or less can occupy the same raceway, cable, or enclosure if all conductors have an insulation voltage rating not less than the maximum circuit voltage. It takes the incoming power and safely distributes it to different circuits throughout your building. However, the key to. When an electrical box is overfilled with wires, it can lead to overheating, increased risk of short circuits, and potentially fire hazards. This 100amp sub feeds a kitchen (fridge, microwave, dishwasher, gas range), a bathroom, 3 bedrooms, and a living room.