March 18

What is a Short?

Car Maintenance


What is a short?

This term is used almost universally when describing an electrical problem; and nine out of ten times it is used incorrectly. Before we discover exactly what a short is, let’s take a look at how electrical circuits work using a simple lighting circuit as an example.

In your car, power flows out of the battery’s negative terminal, through a wire to the light bulb, out another wire to the switch, and via another wire, completes the circuit to the battery’s positive terminal. As you can see, the circuit has a certain ‘length’ and several components.

A short circuit means that power flows back to the battery before it runs the full length of the circuit. Usual causes are bare wires rubbing together or a failure inside a component (in our example it would be the bulb).

When a short occurs, nasty things such as melted wiring can be the result. Fortunately, most circuits are protected with fuses; so should a short occur, the fuse will blow, and break the circuit to protect wires and components.

Although shorts do occur, what more frequently happens is an open circuit. This is when a connection breaks and a circuit cannot be completed. Usual causes are broken wires, broken connectors, defective switches or failure inside a component. The result is often the same as a short (the light does not come on) but the cause is different.

So when one of your electrical devices doesn’t work, it could just as easily be an open rather than a short. And that’s the long and short of it.

About the author 

Bernie Pawlik

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