How do I cut power inside a main panel when there's no service disconnect present?
There's really nothing wrong with plugging a new breaker into a &quot;hot&quot; panel. But if you're not comfortable doing it, then you need to hire an electrician.
You are already aware that the exposed plates that run behind all of the breakers and the &quot;blades&quot; that the breakers grab onto carry line voltage, right?
As long as the breaker itself is in the &quot;off&quot; position, you can install it into the panel. Just keep your fingers away from that exposed plate.
In fact, if it were me, I'd put another double breaker into the other unused position (at least temporarily) in order to cover up the rest of that plate while I pull the new wire into the box and connect it to the breaker.