Determine where you want the sub-panel and install it following the manufacturer's directions. Put it where there are no obstacles so it is easy for you to reach and work on.
Run the cable from the sub-panel to the service panel. The type and size of cable you use and how you run it depend on your specific environment and electrical code. For example, if you want 100 amps for a sub-panel in your outside workshop, you'll want to use #4 copper UF cable.
Turn off the power to the main panel and connect the cable from the sub-panel. Connect the red and black wires to the breaker and seat it into the main panel. Insert the white and ground wires under separate screws on the neutral bus.
Remove the tie bar that connects the neutral and grounding buses from the sub-panel. Grounds and neutrals can share a bus in the main panel, because the current will return to the meter, but they must be separate in any sub-panels to avoid sending current through the grounds of any connected appliances or pipes.
Connect the other end of the cable to the sub-panel. Secure the red and black wires to the terminals on the top of the hot bus, one wire per terminal. Connect the white wire to the top of one side bus to make it your neutral bus. Connect the ground to the top of the other side bus to make it your ground bus.
Remember, when running circuits to the sub-panel, attach the white neutrals from the circuit cables to the neutral bus and the grounds to the ground bus. Never mix them. If you are installing 240-volt circuits, it won't matter, because the white neutral goes into the breaker.
Things You Will Need
- Voltage tester Screwdriver Wire cutter/stripper Pliers Four-conductor cable
- Use main breakers in sub-panels, even though they aren't required. It could save a life. Ground sub-panels in exterior buildings with ground rods--just like a main service panel--to avoid possibly sending any surges into your house. Use copper cable rather than aluminum, if possible.