Fixing electrical things around your home sometimes means electrical service panel repair. The electrical service panel is where utility wires deliver electricity for distribution to the many circuits in your home. This Fix-It Guide tells how an electrical service panel works, what often goes wrong, how to identify an electrical service panel problem, and what parts and tools you will need to fix it. It then gives instructions for how to reset a tripped circuit breaker as well as how to perform screw-in fuse replacement, cartridge fuse replacement, and how to test a circuit breaker. If you’ve checked the electrical device and the electrical receptacle, but haven’t found the problem yet, maybe it’s in the service panel, which is sometimes called the main or the fuse box.
How Does an Electrical Service Panel Work?
The electrical service panel is the main panel or cabinet through which electricity is brought into the building and then distributed to various branch circuits. Power from the utility company (or your solar power system!) enters the panel through three large wires–two hot and one neutral. The main neutral wire connects to a neutral bus or common bar, and the two hot mains connect to the main power shutoff, either a large circuit breaker or a pull-out fuse.
Each of the two bars carries 120 volts. All circuit breakers or fuses in the service panel are connected to one or both of these bars. Fuses and breakers rated at 120 volts are attached to a single hot bar; 240-volt breakers or fuses are attached to both hot bars.
Each 120-volt circuit has a black or color wire connected to a circuit breaker or fuse; the white wire is connected to the neutral bus bar. Ground wires also lead to a neutral bar. Power runs through each fuse or breaker and then out of the panel via a hot wire to whatever receptacles, lights, or appliances are on the circuit. White neutral wires bring power back to a neutral bus bar in the service panel, completing the loop, also known as an electrical circuit.
What Can Go Wrong with an Electrical Service Panel?
Electrical service panels have components inside them that are designed to fail: fuses or circuit breakers. They form the first line of defense for your home, protecting you and your family from electrical fire and shock. An overloaded circuit blows the circuit breaker or fuse–the weakest link–in the circuit. It’s fixable or replaceable.
Never touch the bus bar inside an electrical service panel unless the main breaker has been turned off or the main fuse removed.
How Can I Identify an Electrical Service Panel Problem?
Electrical service panels are not locked boxes. You can open them, look at them, and replace a fuse or restart a circuit breaker without hurting anything. Think of it as the electrical safety panel.
- If an appliance or light won’t turn on, try switching on another light or appliance on the same circuit. If that doesn’t work either, check the service panel for a tripped circuit breaker (see below) or blown fuse (see below).
- If a circuit breaker keeps tripping for no apparent reason, test the circuit breaker and replace it if it is faulty (see below).
If you’re not sure exactly how safe your electrical service panel is, hire an electrician to take a look at it– before there’s a problem.
What Do I Need for Electrical Service Panel Repair?
You can find replacement fuses, circuit breakers, and even electrical service panels at larger hardware stores and home improvement centers. In addition, about all you may need are:
- Screwdrivers (for removing the cover, not for touching electrical wires!)
- Fuse puller (if the box includes fuses)
When making a repair, knowing which circuit controls which outlet speeds the job and makes working safer. That’s why modern electrical codes require service panels to have an index telling which receptacles, lights, and appliances are on which circuit. If your panel has no index, creating one takes a couple of hours and a helper. Here are the steps:
- Draw a rough floor plan of your house, noting the location of every receptacle, switch, light, and appliance. On the service panel, place a numbered piece of tape next to each breaker or switch.
- Turn on all the lights in the house. Plug a light, fan, or radio into as many receptacles as possible, and switch them all on. Turn on the dishwasher and open the door of the microwave.
- To communicate with your helper, use a pair of walkie-talkies or two cell phones. Start at the top of the panel. Switch off the circuit and have your helper identify the room without power. On the map, jot down the number of the circuit next to each outlet that is turned off. Repeat these steps for each circuit. Be aware that some circuits may control multiple rooms and some rooms may contain multiple circuits.
- Write an index that accounts for all the fixtures, receptacles, and hardwired appliances in your home. Attach the index to the inside door of the electrical service panel. Some circuits may wander through several rooms. This can be confusing, but it is not dangerous.
What Are the Steps to Electrical Service Panel Repair?
Reset a tripped electrical service panel circuit breaker:
- Inspect the ends of each circuit breaker in the service panel, looking for one that has its switch leaning toward the off side rather than on. Some circuit breakers, instead, have a red button that can pop out if tripped.
- Once you find a tripped breaker, check the circuit index on the inside of the panel to determine what circuit the breaker controls and make sure everything inside the home that’s on this circuit is off or unplugged.
- Reset the circuit breaker switch or button. If it immediately trips, the problem is probably in the circuit’s wiring; you’ll need an electrician.
- Replug any appliances or other electrical devices or turn on lights in the problem circuit to see if they trip the circuit breaker again. If so, the problem is in the device. If not, everything is probably okay.
Replace an electrical service panel screw-in fuse:
- Examine the fuse for tell-tale damage. Screw-in fuses typically have a glass that allows you to inspect the metal strip inside; a damaged strip means the fuse is blown and requires replacement. If the metal strip is broken completely, the circuit was overloaded. If the fuse window is blackened, the cause is a short circuit–meaning that somewhere wires are touching each other or a wire is making contact with metal.
- If you find a fuse that is blown, remove the fuse and replace it with one of the exact amperage (15- 20- or 30-amp).
Replace an electrical service panel cartridge fuse:
- Turn off the power. Use a fuse puller to remove the cartridge fuse.
- Test the cartridge fuse by touching both ends with the probes of a multimeter set to measure resistance. If the fuse tests for low resistance, called continuity, it is good. If not, it has blown.
- Replace the fuse with an exact replacement.
Test an electrical service panel circuit breaker:
- Touch the prongs of a multimeter to the breaker’s terminal screw and a ground. If there is no power, the breaker is faulty and requires replacement.
- Shut off the main circuit breaker or switch and remove the cover to the electrical service or circuit breaker panel.
- Loosen the screws holding the damaged breaker and pull it from the panel. Identify and remove the wires connected to the circuit breaker.
- Replace the circuit breaker with one of the exact amperage (15- 20- or 30-amp), attaching the wires into the new breaker. Mount and fasten the replacement circuit breaker. (Some circuit breakers snap into place in the panel while others require screw fasteners.)
- Restore power and test the circuit.
When working around an electrical service panel, wear rubber-soled shoes so that you don’t conduct electricity. If the floor by the panel is wet, lay down some boards and lay a rubber mat on top of the boards before continuing. Water is a great conductor of electricity–and your body is mostly water!