" so you think it's a good idea to add an outlet in the garage. The problem is there is no more breaker space! You decide to add another wire to an existing breaker with a wire. This is called "double lugging" and it can be very dangerous. This can overload the breaker causing it to trip more often or worse cause a fire. Hire a Licensed electrician for all you upgrades, don't be the weekend warrior who burned down the house just for one extra outlet."