Turn off the main power and verify the circuit is de-energized with a tester
Check local electrical codes and obtain any required permits
Choose a subpanel rated for the intended load and number of circuits
Select a feeder breaker in the main panel sized to match the feeder conductors and subpanel rating
Run a proper feeder cable or individual conductors from the main panel to the subpanel
Use the correct wire gauge for the feeder amperage and distance
Install a four-wire feeder: hot, hot, neutral, and ground
Connect the two hot conductors to the feeder breaker in the main panel
Connect the neutral conductor to the main panel neutral bar
Connect the ground conductor to the main panel ground bar
Mount the subpanel securely in the desired location
Connect the two hot feeder conductors to the subpanel main lugs or main breaker
Connect the neutral conductor to the isolated neutral bar in the subpanel
Connect the ground conductor to the separate ground bar in the subpanel
Keep neutral and ground bars isolated in the subpanel
Bond the ground bar to the subpanel enclosure if required by the panel design
Add branch circuit breakers in the subpanel as needed
Connect branch circuit hot wires to their breakers
Connect branch circuit neutrals to the neutral bar
Connect branch circuit grounds to the ground bar
Label all breakers and circuits clearly
Reinstall covers and verify all connections are tight
Restore power and test the subpanel circuits
Inspect for proper operation and correct any issues before use