Reading Your Electrical Panel and Its Breakers

Why this matters

Your electrical panel is the one piece of the electrical system you are meant to touch, and only part of it. Knowing how to read it lets you find a tripped breaker in seconds, shut off a circuit before a light fixture is changed, and give an electrician the facts they need on the first call. Knowing what not to touch keeps you clear of the part of the panel that can kill.

This card shows what is on the face of a typical home panel, what each part means, the one part you may operate and the part that stays closed, and the signs at the panel that mean you call an electrician now.

If something is wrong at the panel right now

Before reading anything else: if the panel is buzzing loudly, crackling, smoking, sparking, too hot to keep a hand on, or has water on it or dripping into it, do not open the door or touch any breaker. If there is smoke or flame, get out and call 911. If there is water, stay out of any water near it and call your electric utility to cut power at the meter. Otherwise, call an electrician now. See related: When to Stop and Call a Licensed Pro Around the House.

What you are looking at

Open the panel door (the hinged door on the front) and you see the breakers and, usually, a directory card. Here is a simplified panel face.

+--------------------------------------------------+
|             [ MAIN 100 ]  two-handle main,       |
|                           shuts off everything   |
+------------------------+-------------------------+
|  1 [ 15 ] Bedroom 1    |  2 [ 20 ] Kitchen ctr   |
|  3 [ 15 ] Bedroom 2    |  4 [ 20 ] Kitchen ctr   |
|  5 [ 20 ] Bath GFCI    |  6 [ 30 ]=Dryer         |
|  7 [ -/- ] TRIPPED:    |  8 [ 30 ]=  tie bar     |
|      handle in middle  |                         |
|  9 [ 15 ] Hall lights  | 10 [ 40 ]=Range         |
| 11 [    ] open space   | 12 [ 40 ]=  tie bar     |
+------------------------+-------------------------+
| DIRECTORY CARD: inside the door, lists 1 to 12   |
+--------------------------------------------------+
  ON: handle toward the center   OFF: toward the edge

The main breaker. Usually the large breaker at the top, with a number on it such as 100, 150 or 200. That number is the rating in amps for the whole panel. Switching it off cuts power to every circuit in the panel. Some homes have the main disconnect outside instead, at or near the meter, and the panel inside has no main at all; newer homes may have both.

Branch breakers. Each one protects one circuit, a run of wire that feeds a set of outlets, lights or one appliance. The number on the handle (15, 20, 30 and so on) is its rating in amps. That rating is matched to the size of the wire it protects.

Double-pole breakers. Two handles joined by a tie bar, taking two spaces. They feed 240-volt appliances: dryer, range, water heater, air conditioner, well pump. Both handles move together, and both halves trip together.

A tripped breaker. When a breaker trips, its handle usually moves to a middle position, neither fully on nor fully off. On some panels it goes all the way to off. On others it barely moves, and you find it by looking for the one handle that is not lined up with its neighbors, or by feeling for the one that is loose.

Open spaces. Empty slots, usually covered by a small knockout plate in the cover. A missing plate leaves an opening into the live interior and needs to be closed by an electrician.

The directory card. The list on the inside of the door that says which breaker feeds what. It is only as good as whoever filled it in. See related: How to Label Your Electrical Panel Directory.

Breakers that look different from the rest

Not every breaker is a plain handle. Three kinds are worth recognizing:

• Breakers with a test button. A small button, often colored, on the face of the breaker. These are GFCI breakers (shock protection), AFCI breakers (arc protection), or dual-function breakers that do both. When one trips, it may show a small indicator. You reset it the same way as any breaker, once. See related: GFCI and AFCI Protection in Your Home Explained.
• Twin or tandem breakers. Two thin handles squeezed into one space, not tied together. Each one is a separate circuit. They are a way to fit more circuits in a panel, and whether a given panel allows them is printed on its label, which is the electrician's to read.
• A double-pole breaker with no tie bar, two separate handles sitting side by side on a 240-volt circuit. A missing tie bar means one half can be switched off while the other stays live. Do not try to fix it; mention it to an electrician.

What you may touch, and what stays closed

The breaker handles: yours. You may switch a breaker off to stop power to a circuit, switch it back on, and reset a tripped breaker once. To reset, push the handle firmly to the full off position first, then back to on. A tripped breaker will not reset if you push it straight from the middle to on. If it trips again right away, leave it off and call an electrician. See related: How to Reset a Tripped Breaker Once.

The panel door: yours. You may open and close the hinged door.

The panel cover: not yours. Behind the door, the breakers stick out through a metal plate that is screwed to the box. This is called the dead front, or the panel cover. Behind it are the bus bars and the service conductors coming in from the meter, which stay live even when the main breaker is off. Never remove it. There is nothing behind it a homeowner needs to reach, and an electrician removes it only with the right protective gear and training.

Never put in a bigger breaker. If a 15-amp breaker keeps tripping, swapping in a 20 does not fix anything; it lets the wire behind it carry more current than it is built for, and the wire becomes the weak point instead of the breaker.

Warning signs at the panel

These mean call an electrician soon, or now, even if everything still works:

• Warmth. A panel cover or a single breaker that feels noticeably warm to the touch.
• Sound. Buzzing, crackling or sizzling, other than a faint hum.
• Smell. A hot plastic or burning smell near the panel.
• Marks. Scorching, melted plastic, discoloration around a breaker.
• Rust or water stains on the door, cover or inside the door. Water has been getting in from somewhere.
• A breaker that will not stay on, or that trips with nothing plugged in.
• Flickering lights across the house, or lights that brighten and dim when a large appliance starts.

Some older panel designs, from a few manufacturers in particular decades, are known among electricians for breakers that may not trip when they should. If your home has an older panel and you have never had it looked at, it is a fair question for an electrician on any visit; they will recognize those panels on sight.

Worked example: reading the panel before the electrician's call

A homeowner wants to add a 240-volt circuit in the garage for an electric vehicle charger. Before calling an electrician, she reads her panel so the call starts with facts. She only looks, opens the door, and counts.

The main. The main breaker reads 100. The panel has a 100-amp rating.

Counting the spaces. The panel has 30 spaces. She counts what is in them:

• Single-pole 15-amp breakers: 8, taking 8 spaces
• Single-pole 20-amp breakers: 9, taking 9 spaces
• Double-pole breakers: dryer 30, range 40, air conditioner 30, water heater 30. Four breakers at two spaces each: 8 spaces

Spaces used: 8 plus 9 plus 8, which is 25. Spaces open: 30 minus 25, which is 5.

The number that tempts people. Adding up the handle ratings gives 8 x 15 = 120, plus 9 x 20 = 180, plus 30 + 40 + 30 + 30 = 130, for a total of 430. That is more than four times the 100-amp main. It looks alarming and it means nothing: circuits are never all fully loaded at once, and adding handle numbers is not how anyone sizes a service. She does not use it.

What the count does and does not tell her. Five open spaces mean there is physically room for a double-pole breaker, which takes two. It does not mean the house has the capacity for a charger. On a 100-amp service already carrying an electric range, dryer, water heater and air conditioner, the question is the total load. An electrician answers that with a load calculation under the National Electrical Code (NEC) as your jurisdiction has adopted it, and may suggest a smaller charger circuit, a load-management device, or a service upgrade.

The call. "I'd like a circuit for an EV charger in the garage. My panel has a 100-amp main and 30 spaces, 25 used and 5 open. It already feeds an electric range, dryer, water heater and central AC. I have a photo of the panel and the directory." The electrician knows before arriving that the load calculation is the real job.

What would change it. A 200-amp main with gas appliances instead of electric ones would make the charger much more likely to fit without an upgrade. A panel with no open spaces at all would add a question about how to make room. Either way, the answer is the electrician's to give.

Keeping the panel usable

• Keep the area in front clear, at least enough to stand squarely in front of it and open the door fully. Electrical code sets working-space clearances in front of panels for this reason. Do not store things against it or build shelves in front of it.
• Keep a flashlight nearby. The time you need the panel most is often when the lights are out.
• Photograph the panel face and the directory and put the photos in your house records. See related: Your House Records File and What Goes In It.

References

• National Electrical Code (NFPA 70), in the edition your jurisdiction has adopted, which governs panel work, load calculations and working space and binds the electrician who does the work
• See related: GFCI and AFCI Protection in Your Home Explained
• See related: Your Home's Shutoffs: Water, Gas and Electric