Each circuit has a ‘breaker’ attached to it, in line, so if someone sticks a fork in the light socket in the master bedroom, the breaker will trip and cut off electricity down that spoke. It’s a safety mechanism.
The size of the breaker is also determined by the amount of electricity needed.
There are two main reason Electric Panels need to be upgraded.
1. Electric panel age. After 15-20 years a panel begins to break down and must be replaced to be safe.
2. Electric panel size. When more circuits are added (more spokes) the panel runs out of capacity. Therefore a new panel (usually but not always) must be installed.
In all states in the USA a certified and licensed electrician is required by law to do most electrical work. Doing a complete panel upgrade is not an easy task, and if done incorrectly you can have the light switch in your bedroom turn on the garbage disposal, or open the garage door! In California the license is C10 for a dedicated electrical contractor. A general contractor with a B license can also do the work, but they generally have to hire a C10 licensed person to actually do the work.
Penna Electric in Manhattan Beach and Los Angeles does electric panel service and upgrades and is a C10 AND B all in one company. You can also contact them at 877-415-0097.