Electrical components

The panel distributes power and holds the overcurrent protection. Its rating (100A, 150A, 200A, 400A) describes the service capacity, and the number of available slots describes how many more circuits you can add. Those are different limits — a panel can be at capacity on slots but not on amperage, or the reverse. Ask which one is your constraint, because tandem breakers or a subpanel may solve a slot problem far more cheaply than a full service upgrade.

Breakers come in standard, GFCI, AFCI and dual-function types. GFCI protects people from shock by detecting current leaking to ground; AFCI detects the signature of arcing, which is the failure mode behind a large share of electrical fires — ESFI attributes over 28,000 residential fires a year to arcing faults. This Old House puts these specialty breakers at roughly $35–$60 each, which is why a panel upgrade that adds many of them costs more than the panel alone suggests.

The service entrance — meter base, service conductors, mast — is the part homeowners forget. It is often what makes a panel quote jump. This Old House puts meter box replacement at $1,800–$3,500 installed. If your quote is high, this is the first line item to ask about.

Grounding and bonding is invisible and unglamorous and is what keeps fault current from finding a person. It is not an area to value-engineer out of a quote.

How to choose

Slots vs. amps: ask which one you are out of

A full panel is not the same as an undersized service. A subpanel ($400–$1,750, per This Old House) may cost far less than a service upgrade.

Breakers must match the panel

Breakers are listed for specific panel types. Using a different brand than the panel is listed for is a real compliance and safety issue. Ask what is being installed.

Do not skip AFCI/GFCI to save money

These are the devices that address the actual failure modes behind shocks and arcing fires. At $35–$60 per breaker they are the cheapest safety spend in the whole project.

Ask whether the utility side needs work

The meter base and service conductors may belong to you even though the drop belongs to the utility. Who does what — and who pays — should be settled before work starts.

Photograph the panel label before and after

Keep a picture of the panel directory and the label. It makes future work faster and gives you a record of what was actually installed.