Adding a Sub Panel if you run out of circuit breaker space. Here is a Step by Step procedure for adding a sub panel to the main electrical service panel of a home to expand the circuit breaker capacity of an existing electrical panel that has run out of circuit breaker space. This can also be used to add a panel for a workshop, garage, or an outbuilding. DIY Electrical Wiring from an Electrician. Complete with an easy to understand example and process which is explained by a licensed electrical contractor.