What Is a Short Circuit, and What Causes One?
Electricity powers nearly everything in our homes, and it’s a beneficial force when handled properly. But when electricity goes wayward, it’s a damaging, dangerous, and frightening event called a short circuit. Short circuits can be prevented and managed with planning and a healthy respect for electricity.
What Is an Electrical Short Circuit?
A short circuit is an abnormal condition in an electrical circuit where the electrical current flows through an unintended, shorter pathway instead of following the circuit.
An electrical circuit is a circular flow of energy from a home’s electrical service panel and back again. This flow is continuous and unbroken. Items along the circuit such as outlets and lights only borrow from the circuit; they do not break the circuit.
Electricity likes to flow along the path of least resistance. Copper is used for electrical wires because it conducts so well, while materials like wood or fiber would be highly inefficient materials for wiring because they resist electricity. Even steel and iron are poor materials for wiring, though better than wood or fiber.
The long path for the energy to flow back to ground is on the circuit. But when a shorter path is provided, electricity naturally seeks this route—the path of least resistance. The electricity immediately changes its course to head to ground by this shorter, easier path.
What Causes Short Circuits
Short circuits can be caused by:
- vermin or pests chewing through wires
- water or other fluids coming into contact with electrical wiring
- loose connections in an electrical box
- old or damaged outlets, switches, lights, appliances, or other electrical devices
- nails or screws piercing through walls and coming into contact with wires
- deterioration of electrical cable sheathing
- build-up or surges of electricity
Types of Short Circuits
Normal Short Circuit
In a normal short circuit, a powered or hot wire touches a neutral wire. Immediately, resistance drops and current begins to move in another path.
Ground Fault Short Circuit
In a ground fault short circuit, a powered or hot wire touches a grounded section of a box, device, appliance, outlet, bare ground wire, or anything else supplied by the electrical circuit.
Signs of a Short Circuit
Previous Short Circuits
Short circuits often do not announce themselves until the moment they happen. In some cases, though, there may be a warning sign of a previous short circuit.
This may be in the form of a charred wire or light switch. If the short circuit was recent, you may sense a metallic smell. Or you may smell burned plastic or rubber.
Ongoing Short Circuits
When a short circuit happens, the circuit breaker usually shuts off. Sometimes, there are sparks and a bright light. A loud zapping sound or a boom can accompany a short circuit.
The device powered by the electrical current stops working. GFCI outlets will trip off.
If you are touching the device or if your body happens to be the short within this short circuit, you may receive an electrical shock and often a burn from the intense heat.1
Why Short Circuits Are Dangerous
When the human body is introduced as the path of least resistance, the current travels through the body. Short circuits can cause injury or death through electrical shock, electrocution, or fires.1
More power is demanded during a short circuit, causing electrical arcs and extremely high temperatures that can melt plastics or set fire to flammable materials such as wood or fabrics.
How to Fix Short Circuits
Electric service panels, or circuit breaker boxes, can be dangerous. Leave the dead-front cover in place, since it covers the energized metal lugs. The lugs remain live even after the main breaker has been turned off.
Identify the circuit. Make sure that you’re dealing with only the circuit in question.
Make Circuit Safe to Work on
Turn off and remove the circuit breaker. Remove the breaker by rocking it back toward the side of the electric service panel. The breaker should lift off.
Identify all devices on the circuit, including outlets, switches, appliances, lights, A/Cs, and more—even junction boxes.
Check the outside of each device on the circuit. Look for blown fuses on individual devices. Look for signs of a short circuit: sharp smells, melted plastic, or burn marks.
Look Inside Devices
Where practical, check wires in each device. Open up electrical boxes and check connections. Look at junction boxes that aren’t attached to devices. Remove light fixtures and look inside the fixtures and inside their electrical boxes.
Check Cables in Walls and Attics
Where you can, examine wires between devices. Since wires are generally closed up in walls, this may be difficult. But often, wires run along the joists in attics and can be examined with a flashlight.