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Tips & Tricks Blog

Using a Multimeter at Home


Electrical wiring and diagram

When you have an electrical problem in your home, you can’t go wrong by calling a licensed electrician. But if you’re thinking about taking more of a DIY approach to electrical maintenance, one way to get started is to spend a few dollars on a digital multimeter.

A multimeter doesn’t fix anything, but it can help you test and measure the voltage, amperage and electrical resistance of any circuit in your home. They’re inexpensive -- $10 is plenty for a multimeter that offers the basics -- and fairly simple to use, though they can appear intimidating at first. The multimeter dial contains several symbols you might not see everyday.

Understanding Your Multimeter Dial

Your basic multimeter will have a dial that you’ll use to indicate what type of measurement you want to take. Voltage indicators are labeled as DCV for direct current voltage and ACV for alternating current voltage. You’ll use the former for testing batteries and the latter for testing outlets, fixtures, appliances and electronics.

When measuring electrical resistance, look for the omega symbol, which looks like a horseshoe. And when testing continuity, choose the diode symbol, which looks like an arrow pointing to the right. Resistance tells you how easily electricity can flow through a circuit, and continuity verifies whether a circuit is complete or broken.

Most multimeters will also let you measure direct current amperage (look for the DCA label) but not all models measure alternating current amperage (ACA). There may be additional settings for functions like measuring temperature, direct current gain, frequency or special functions for testing common batteries by size.

Plugging In the Probes

While you get your readings from the multimeter itself, you can only test electrical sources with the use of compatible probes. You should see at least three ports for probes, usually labeled “COM”, “mA” and “10ADC”.

COM stands for common and is where you plug in the black probe. The red probe will go either in the mA port if you’re measuring a voltage or current of less than 200 milliamps (mA) or in the 10ADC port if you’re measuring voltage or current greater than 200 milliamps. When in doubt, use the 10ADC port.

Using Your Multimeter

Before using a multimeter on any live or potentially live power source, you should read the user’s manual for your specific model and pay particular attention to the safety guidelines. This is not only the best way to familiarize yourself with the specific functions of your multimeter, it’s an important review to minimize the risk of electric shock. Using a multimeter with probes that are improperly connected could also result in the multimeter smoking, catching fire or even exploding.

But once you’re familiar with your multimeter and how to use it safely, there are simple investigations you can use it for right away. Let’s say you find a loose battery in a drawer and want to know if there’s still energy stored inside. Simply connect the probes to your multimeter and turn the dial to the highest DCV setting, since batteries use direct current. Touch the red probe to the battery’s positive terminal and the black probe to the negative terminal, and you’ll see the voltage reported on the digital display.

Common batteries like AA, AAA, C and D hold 1.5 volts at full charge, while 9-volt batteries hold nine volts, of course. If the reported voltage is lower than these amounts, you know that some of the battery’s power has been discharged.

You can also use a multimeter to test a wall outlet you think might be malfunctioning. Set your multimeter to the highest ACV setting and, while holding both probes in one hand, insert the red probe into the small slot and the black probe into the larger slot. If the outlet is functioning normally, you should see a voltage of 120 or slightly lower. If you get a zero or a number lower than 110, you know there’s a problem.

Exploring your electronics, batteries and home electrical system using a multimeter can be a fun way to learn the basics of electricity, provided you always put safety first. But whenever you encounter an electrical problem that’s beyond your abilities, be sure to call upon the licensed electricians at your local Mister Sparky.

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