To read a breaker panel, open only the outer door, not the screwed-on cover behind it. The largest switch is the main breaker and its number is the whole home's amperage. Each smaller breaker's number is the amperage of one circuit, and a double-width breaker feeds a 240-volt appliance. A tripped breaker sits between on and off, and you reset it by pushing it firmly to off first, then back to on. Everything behind the cover is a licensed electrician's work.
That is the entire homeowner-side job. This page is about reading, labeling and recognizing, and it is written for homes in the United States and Canada, where the panel is fed at 120 and 240 volts. If a step here would have you removing a cover, testing a conductor or tightening a screw inside the enclosure, it does not appear, because that work is not a matter of care or confidence: it is licensed work with live parts a few inches away.
What you are looking at when you open the door
The panel is a metal box, usually in a basement, garage, utility room, hallway closet or on an exterior wall. It has a hinged outer door. Open it and you see two things: a column or two of breaker handles, and a paper directory glued inside the door.
The main breaker. Usually at the top, sometimes the bottom, and physically larger or wider than the rest. It switches the whole house. The number printed on it is the service size, commonly 100, 150 or 200 amps in a modern home.
The branch breakers. The rows of smaller switches. Each one protects one circuit: a room's outlets, the lights on one floor, one appliance.
Single and double breakers. A single-width breaker is a 120-volt circuit: lights, general outlets. A double-width breaker, with its two handles tied together, is a 240-volt circuit for a large appliance such as an electric range, a dryer, a water heater or an air conditioner.
Test buttons. Some breakers have a small button marked TEST. Those are ground fault or arc fault breakers, which protect against shock and arcing respectively. The button is a test function the manufacturer put there for the homeowner, and pressing it should trip the breaker, which you then reset.
The directory. The paper list saying which breaker does what. In most houses it is wrong, or half filled in by somebody in 1998. Fixing it is the most useful thing on this page.
How to read a breaker panel's numbers and labels
The numbers are not a mystery, but they are not a rating of how much power a room needs either. They describe the point at which the breaker cuts off to protect the wire behind it.
| What you see | What it means | What it does not mean |
|---|---|---|
| 15 or 20 on a single breaker | A 120-volt lighting or outlet circuit | Nothing about how many devices you can add |
| 30, 40 or 50 on a double breaker | A 240-volt appliance circuit | That the appliance draws that much continuously |
| 100, 150 or 200 on the main | The size of the electrical service to the house | That you have unused capacity to spare |
| A small TEST button | A ground fault or arc fault breaker | That it needs testing by taking anything apart |
| A blank space with a filler plate | An unused position | An invitation to add a circuit |
Two things worth knowing about the main number. A house with a 100-amp service and a growing list of large appliances may be at its limit, and that is a question for a licensed electrician with a load calculation, not something you resolve by reading the panel. And the number on the main tells you nothing about the condition of the panel, which is a separate question and also theirs.
What a tripped breaker looks like, and how to reset one
A breaker has three positions, and the third one is the one people miss. On, off, and a middle position that looks almost on. Run a finger down the row: the tripped one is the handle that is out of line with its neighbors, and it often feels loose or springy compared with the others.
To reset it, push the handle firmly all the way to off first, then back to on. A breaker will not reset if you only nudge it from the middle position toward on, which is why people conclude their breaker is broken when it is not.
Before you reset anything, unplug or switch off whatever was running when it tripped. A breaker that trips is doing its job, and putting the same load straight back on it just repeats the event.
Then stop and read the outcome, because this is the fork in the road. If it resets and stays on, the circuit was overloaded and you have learned something about what not to run together. If it trips again immediately, or trips again later on the same circuit, that is not something to keep resetting. The Electrical Safety Foundation International's guidance on breakers, read on 2026-09-08, is that frequent trips of a breaker indicate a problem and should be inspected by a qualified electrician. Never tape, wedge or otherwise hold a breaker in the on position.
Mapping the panel properly, so the directory is true
This is a two-person, one-afternoon job and it is worth every minute of it.
Plug a lamp or a small radio into an outlet, or station somebody in the room. Turn off one breaker. Note every light, outlet and appliance that went dead. Turn it back on and move to the next. Write it down as you go and put the finished list on the door, in ordinary language: "kitchen counter outlets, south wall" beats "kitchen 1".
Some sensible cautions before you start:
- Warn the household. Somebody is working on a computer, and the freezer does not enjoy this either.
- Do not switch off a circuit feeding medical equipment, and be careful around anything with a clock, a program or a pump that will not restart happily.
- Leave the main alone. You are mapping branch circuits, and switching the whole house off tells you nothing.
- Expect surprises. Rooms frequently share circuits, and an outlet in one room is often on the circuit of the room next door.
ESFI's own advice includes labeling your panels so you can quickly turn off and restore electricity when necessary. A true directory is what turns the panel from an intimidating box into the most useful thing in the house during a small emergency.
Is it the circuit or the appliance? A short diagnostic
When something stops working, the panel answers half the question and the appliance answers the other half.
If everything on one circuit is dead, the breaker is the first place to look. If the breaker is fine and the circuit is still dead, that is an electrician.
If one appliance is dead and everything else on its circuit is working, the circuit is not your problem. A vent hood that does nothing at all, for example, is far more often a switch, a fuse in the unit or a failed motor than a panel event, and a range hood that has stopped working walks through that in order.
If an appliance runs but does not do its job, the panel is not involved at all. A refrigerator with power and a warm interior is a sealed-system or airflow problem, and a refrigerator that is not cooling starts where it should.
If the breaker trips only when one appliance starts, that appliance is the suspect. Motors draw hard on startup and a failing one draws harder. That is a service call for the appliance, and if it is an old machine it may also be a moment to run the numbers on whether to repair or replace it rather than pay for a diagnosis on something at the end of its life.
The cover stays on. Here is exactly why
The hinged door you opened is not the cover. Behind the door is a flat metal panel held on by screws, called the dead front, and its whole purpose is to keep you away from what is behind it.
Behind that cover, the conductors that feed the main breaker come in from the utility. They are on the supply side of your main breaker, which means your main breaker does not switch them off. Turning the main off de-energizes the branch circuits in your house and leaves those service conductors live. This is why "I turned the main off first" is not a safety plan, and it is the single most important sentence on this page.
There is no reading task that requires the cover to come off. Everything a homeowner needs, the directory, the amp ratings, the tripped handle, is visible with the cover in place.
ESFI's do-it-yourself electrical safety guidance, read on 2026-09-08, recommends hiring a qualified, licensed electrician to perform any electrical work in your home, and says plainly that most homeowners do not have the training or experience needed to safely perform home electrical work, which increases the risk of immediate injuries and electrocutions. It also gives the rule that covers everything this page does not: never attempt a project that is beyond your skill level.
Call an electrician today, not eventually
Each of these is an immediate call rather than a wait-and-see.
- A burning smell, or a smell of hot plastic, anywhere near the panel. Immediate.
- A panel that is warm to the touch, or that buzzes, hums, crackles or ticks. Immediate.
- Scorch marks, discoloration, melted plastic or rust inside the door. Immediate.
- Any water on, in or above the panel. Immediate, and do not touch it.
- A breaker that trips again as soon as you reset it, or that trips repeatedly over days. ESFI's own line: frequent trips indicate a problem and should be inspected by a qualified electrician.
- A breaker that feels hot, or a handle that has gone slack and will not stay on.
- Any question about aluminum branch wiring. Homes wired in certain periods used aluminum for branch circuits, and how it is connected is a real safety question with a specific remediation. It is assessed and corrected by a licensed electrician, and there is nothing about it a homeowner should be opening a panel to inspect.
- Lights that dim or flicker across the house when a large appliance starts.
- A panel that is obstructed. Working space in front of a panel is a code requirement, and boxes stacked in front of it are also a problem for you at 2am.
ESFI adds a threshold worth acting on even when nothing is wrong: an electrical inspection is warranted if the home is older than 40 years, or has had a major addition, renovation or large appliance added.
Jurisdiction: whose rules apply to your panel
Electrical installation in the United States is governed by NFPA 70, the National Electrical Code, but the code is not law until a state or municipality adopts it, and jurisdictions adopt different editions and add their own amendments. What a homeowner may legally do to their own electrical system, and what requires a permit and an inspection, is decided by your local authority having jurisdiction, which is usually your city or county building department.
Two practical consequences. First, an article on the internet cannot tell you what is permitted where you live, and this one is not trying to. Second, if you are considering any work on the panel, the building department is the phone call before the hardware store, and in most places the answer will be that the work requires a licensed electrician and a permit.
FAQ
How do I know which breaker is which? Map it with a helper. Turn off one breaker at a time and record everything that goes dead, then write a plain-language directory and tape it inside the door. Assume the existing label is wrong until you have checked it.
What does the number on a circuit breaker mean? It is the amperage at which that breaker cuts the circuit to protect its wiring. Single-width breakers marked 15 or 20 are typically 120-volt lighting and outlet circuits, and double-width breakers marked 30 to 50 are 240-volt appliance circuits.
How do I reset a tripped breaker? Switch off or unplug whatever was running, push the handle firmly all the way to off, then back to on. If it will not stay on, or trips again, stop resetting it and call a licensed electrician.
Is it safe to open my breaker panel? Opening the hinged outer door to see the handles and the directory is normal. Removing the screwed-on cover behind it is not a homeowner task. The service conductors behind that cover are not switched off by your main breaker.
My breaker keeps tripping. What is wrong? Either the circuit is carrying more than it should, or something on it has a fault. Unplug the suspect appliance and reset once. If it trips again, ESFI's guidance is that frequent trips indicate a problem that should be inspected by a qualified electrician.
Does turning off the main breaker make the panel safe to open? No. The conductors feeding the main come from the utility and are not controlled by it. This is the reason the cover stays on and the reason panel work is licensed work.
