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Testing Electrical Circuits


If the thought of working on an electrical circuit makes you cringe because the circuit may still be on or “hot”, then investing in a multi-meter, voltmeter or a neon-light tester should be your first order of business. These testers are relatively inexpensive and can protect you from electrical shock.

1. Testers and How They Work

Tim Thiele

Basically, they consist of a neon light bulb that is attached to two leads used for checking if a circuit is “hot” or “dead”. When you press these two leads into an outlet, the bulb will light if the circuit is “hot” or on. If it doesn’t light, then the circuit is “dead” or off.

Always check to see if the tester is working properly by checking a circuit that you know is working properly before moving on. To double-check that an outlet is actually off, remove the outlet cover and test the screws on the sides of the outlet. You can also plug a lamp or vacuum into the outlet just to put your mind at ease.

2. Outlets and Testing

Tim Thiele

A typical outlet has three holes built into it. The shorter straight slot is the “hot” lead. The longer straight slot is the “neutral” lead. The slot that looks like a small circle hole is the ground.

To test the ground, test between the “hot” and “ground” slots. If the circuit is working and you have a good “ground” connection, the tester will light. The tester will also light if you test between the “hot” and “neutral” slots.

Plug-in circuit testers are available that will test your circuit for you via three neon lights. They test for an open neutral, lack of a ground, wires on the wrong terminals, and no power.

3. Switches and Testing

To test a switch, remove the cover plate and check from one of the screws on the side of the switch to the bare copper wire (ground) or the metal box. Keep in mind that the box may not be grounded, especially if it’s a plastic box.

4. Testing Light Fixtures

When checking light fixture wiring, take down the light and using a “tick-tracer”, test the circuit to see if it working. This tester lights when you place it close to a wire that has current flowing through it.

To double-check the circuit, first turn off the power to that circuit. Now, remove the wire nuts from both the black “hot” wires and the white “neutral" wires. Separate these sets of wires so that they are not touching one another.

Turn the circuit back on and check between the black and white wires with the voltmeter or neon tester. Be careful not to touch the exposed wires. The voltmeter should show a reading of around 120 volts. Likewise, the neon tester should light if the circuit is working properly.

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