Can You Use a Main Breaker Panel As the Subpanel?
A standard 100-amp load center can be used as a subpanel, according to electrical-online.com. The neutral bonding jumper, however, must be removed. In a subpanel, the neutral must be completely isolated from the ground. When doing electrical work, the power should always be turned off.
For residential service, the neutral and ground can only be bonded in one location, which must be in the main panel. In most panels, a metal strap or machine screw connects the neutral bus bar to the panel case, or ground. This metal strap or screw must be removed. To make the sub-feed connection, an appropriate size and length cable is run between the main panel and the subpanel. For example, 6-3 NM-B wiring can carry 50 amps at a maximum length of 55 feet. At the main panel, the hot legs of the sub-feed wiring is connected to an appropriate branch circuit breaker, the neutral wire connects to the bus bar and bare grounds to the panel case. At the subpanel end, the hot legs of the sub-feed wiring are connected to an appropriate circuit breaker seated on the panel's hot bus bar. This acts as the subpanel's main breaker via reverse feeding. The bare wire is connected to a case ground lug in the subpanel, and the neutral wire is connected to the isolated neutral bar. Electrical work should always be inspected by a licensed professional.