How to read your electrical panel

Most people have never looked at their panel with the door open. It is worth five minutes. The panel tells you how much power your house can use, who made it and whether there is room for an EV charger or a heat pump.

Safety rules first

• The outer door is safe to open. It hangs on hinges and carries no power.
• The metal sheet behind the door is the dead-front. It is held on by screws, and the bars behind it are live even with the main breaker off, because the wires from the meter feed the top of the panel. Do not remove it.
• Stand on a dry floor. Do not touch the panel with wet hands or a wet floor.
• Keep the space in front clear. The code calls for a clear area at least 30 inches wide and 36 inches deep in front of a panel.
• If you see scorch marks, melted plastic, rust, water or hear buzzing, stop and call an electrician.

Read the main breaker

The main breaker is the biggest one, usually at the top, with a number on the handle: 60, 100, 125, 150 or 200. This is the size of your service. A 100 amp main means the house is limited to 100 amps total. Older homes often have 100 amps or less. Newer homes more often have 200.

Two things can confuse you:

1. No main breaker in the panel. The main may be outdoors in a meter-main box, or this is a subpanel fed by another panel.
2. Bus rating higher than main. The panel can be built for 225 amps and still have a 200 amp main. The main is the limit.

Find the label and the brand

Inside the door or on the side wall there is a sticker with the brand, model number, voltage and a maximum amp rating. Common names are Square D, Eaton, Siemens, Cutler-Hammer, GE, Murray and Leviton. Two older brands matter for safety: Zinsco and Federal Pacific (Stab-Lok). Electricians commonly replace both. A federal review in 1983 found Federal Pacific breakers failed some lab tests, and Zinsco breakers are reported to overheat. If your label says either one, read about Zinsco and Federal Pacific panels and plan a replacement.

The label also lists which breaker types the panel accepts. Breakers are not interchangeable between brands, and a wrong one can overheat at the bus.

Count the spaces

A residential panel is built with a set number of spaces, often 20 to 40. Count the slots that are empty or covered by a small plate. Each 120-volt circuit uses one space. Each 240-volt circuit, such as a dryer, range or EV charger, uses two.

“Tandem” or “twin” breakers fit two circuits in one space, but only where the panel label allows them. If every space is used, you may still have power left. That is a job for a load calculation, and the fix may be a subpanel rather than a new panel.

Check the directory

The directory is the paper list of what each breaker feeds. An out-of-date one is common. Look for “kitchen,” “dryer,” “AC” and any breaker with no label. Unknown circuits are worth tracing before a project, because an electrician needs to know what is on each breaker.

Also look at the handles. A breaker in the middle position has tripped. If one trips repeatedly, see breaker keeps tripping.

What to photograph

Take clear photos of:

• the open door with all breakers visible
• the label and any model number
• the meter and the wall around the panel
• the garage or yard wall where a charger or new circuit would go

These photos let an electrician judge a job before a visit. See how to prepare for the electrician visit.

When reading the panel means a bigger job

What you saw	What it may mean
60 or 100 amp main with electric heat or dryer	A load calculation, then maybe a 200 amp upgrade
Zinsco or Federal Pacific label	Replace the panel
No free spaces	Subpanel or swapped breakers
Scorch, rust or buzzing	Stop, call an electrician now

As of October 2026, a typical SoCal 200 amp panel swap runs $2,500 to $4,500. Start at the panel upgrades hub if your panel is the limit.