AmpereTally

Most houses that ask for 400 amps need 200 and a load calculation. The ones that do need 400 pay for two panels, a bigger meter socket and usually a new utility transformer connection.

The panel is the cheap part. The meter socket, the service conductors, the grounding and whatever the inspector finds behind the old panel decide whether the bill is $2,000 or $5,000.

A new panel does not give a house more power. Only the service conductors, the meter socket and the utility connection decide how many amps come in.

The answer depends on what the wire feeds. Wire that carries the whole house can be smaller than wire that feeds a garage subpanel on the same 150 amp breaker.

Putting the main breaker outside changes what the panel inside is. Whether it becomes a subpanel, with separated neutrals and grounds and a four-wire feeder, depends on which of three options you choose.

The panel is full and the service feels small. Those are two different problems and only one of them is about amps.

Running out of breaker spaces is a physical problem, not an electrical capacity problem, and the cheap fixes are often the right ones.

The ampacity table says 12 AWG copper can carry 25 amps. The breaker on it is still 20, and NM cable is held to the 60°C column. Those two rules explain most of the chart.

The charger is the small part of the cost. What it does to the service calculation is the expensive part.

A breaker that does not trip is not a breaker. That is the whole of the concern with these two.

In a modern kitchen or laundry room a circuit needs both, and a dual-function breaker is the usual answer. In a bedroom it needs arc-fault protection only.

The electrician's part is usually one day. The permit, the utility's disconnect and reconnect, and the inspection in between set the real schedule.

The grounding system does nothing at all until something goes wrong, which is why it is the part most often found inadequate.