According to the National Electrical Code (NEC), the conductor must be long enough to extend outside the box's opening. This length allows enough room to connect, splice, or terminate wires without strain or damage. The question is, how long should it be?A distribution box is the heart of any electrical system. However, the key to. Electrical clearances set the minimum safe distances for panels, overhead lines, pools, and buried wiring — and ignoring them has real consequences., switches, receptacles, combination devices) - by establishing an equivalent conductor-value for each.