Electrical Circuit Testers

How to Use Electrical Circuit Testers in Home Electrical Wiring

By Mark J. Donovan

When working with electricity, particularly high voltage AC electricity in your home, it is always important to employ a high level of safety precautions.

Part of that safety begins with shutting off power off at the main circuit panel to the circuits that you plan on working on.

The other part of the safety equation is confirming that the power is indeed off at the electrical box or appliance you plan on working on.

To do this requires the use of an electrical circuit tester. There are variety a of electrical circuit testers available on the market today, however there are two that are most commonly used.

High Voltage AC Circuit Tester (a.k.a. – Neon Bulb Tester)

One common electrical circuit tester is the High Voltage AC Circuit tester, or Neon bulb tester. It is inexpensive, requires no batteries, and is easy to store due to the fact that it is so small. Most models will support an AC voltage up to 250V.

To use a High Voltage Circuit tester, just plug the two terminals into the wall outlet, or switch box you plan on working on, making sure that you are holding onto the insulated handles and are not touching the metal probes. If you touch the metal probes while plugging them into a powered outlet or circuit you may be exposed to a life threatening shock.

If the outlet or switch is powered on, the bulb will light up. If it is not, the bulb will remain unlit.

You can also use this type of tester to check if power is flowing through a switch, or on bare wire ends, or even on a circuit breaker. Again, extreme caution should be given while performing any of these types of tests.

Digital Multimeter

Another electrical circuit tester is a digital multimeter. It can be used for a number of electrical circuit testing applications.

First, it can be used to measure High Voltage AC at a circuit breaker, outlet, or switch, using the two probes that come with it.

To use it for this type of test, plug the black lead into the common socket, and the red lead into the Voltage/Ohm socket. 

Then set the dial for 125AC or higher, depending upon the digital multimeter model that you have. Next plug the leads into the outlet or across the switch and read the digital display on the digital multimeter. You should observe a reading of somewhere between 110 and 120V if power is on at the outlet, switch or circuit breaker.

You can also use a digital multimeter for checking connectivity between two points in a circuit. To do this, again plug the black lead into the common socket, and the red lead into the Voltage/Ohm socket. Now set the dial to Ohms, for a resistive load. Now touch the two probes together.

You will notice that the reading goes to a value of Zero, indicating that there is direct connectivity, or a short between the two probes.

You can extend this function for testing the connectivity between a length of wire or un-powered circuit. For, example you can use a digital multimeter to “buzz out” the Romex cables between two electrical boxes.

ETEKCITY MSR R500 Digital Multimeter Review

This situation frequently arises when you are in the process of doing the finished wiring in a room and are not sure which Romex cable end coming out of one box corresponds with another Romex cable end in another box.

By twisting, for example, the black and white wires together coming from the same Romex cable end, you can then check for connectivity between the two wires at the far end, or other electrical box. When you find the Romex cable at the far end box that has a short between the black and white wires (because you tied them together at the other box) you can then label the Romex bundle at both ends.

Digital multimeters can also be used for measuring resistance and current.

Though digital multimeters are more expensive and cannot be as easily stored in a pant or shirt pocket they do offer some significant advantages over High Voltage AC Circuit Testers and are thus well worth the extra investment.

So before working with electricity in your home, make sure you have a High Voltage AC Circuit tester or a Digital multimeter, and always exercise extreme caution by first turning power off at the main circuit panel, and then checking that power is indeed off at the particular electrical box.

Warning: When working with electricity use extreme caution to avoid the risk of electrical shock. Make sure to first shut off power at the main circuit panel and then confirm all power to the electrical fixtures and boxes are off prior to beginning any electrical work.

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