Detecting ' Ghost Voltages' with Extech

Detecting 'Ghost Voltages' with Extech

Tuesday, February 28, 2017


If you’re an electrician, you recognize the value in ensuring personal safety on the job. While conducting a sweep for live voltages, making certain that the power is off on your electrical lines and circuits is crucial for this reason. Imagine your DMM alerts you to a live voltage that you know shouldn’t be there. Not only that, but the reading is askew and irregular. You recognize that the measurement could be a “ghost voltage,” but now you must take the time to ensure that it isn’t faulty wiring, which proposes something much more dangerous.  

Working in the electrical field, you’ve probably fell subject to the inconvenience described in this post before. As you may know, ghost voltages occur when your test (which isn’t receiving power) reads voltage from a nearby electrical source. Usually, this is due to extra and unused wiring in the conduit being tested as it runs along other wires that are receiving power. The longer the run, the more potential for the presence of a ghost voltage. When experiencing peculiar voltage readings in the past, you’ve probably had to dust off that old analog meter or solenoid tester. It’s irritating and time-consuming to stop one task, pull out a new meter and take the time to diagnose an unrelated issue in the middle of your work day. 

EX655Digital Multimeters have made electrical measurements more reliable and efficient, yet, in the case of “ghost voltages,” or, “phantom voltages,” they weren’t able to completely replace analog meters and solenoid testers due to the differences in their impedance. Since digital multimeters are typically preferred and desired test and measurement products for industrial and high voltage measurements, their impedance is high, which allows us to effectively measure for those applications. Conversely, an analog or low impedance device can have problems effectively measuring what a modern DMM can, but will be able to identify ghost voltages much easier because of low impedance. It should also be noted that many of those old analog testers are not up to date with current safety standards. So what’s the solution?

The solution is a dual-impedance multimeter. These DMMs can switch their input impedance with the help of the “LoZ” function. This means you get the functionality of a modern digital multimeter and the ability to quickly identify wiring that is picking up a ghost voltage, ensuring it isn’t a greater issue and saving you time and hassle.Luckily, Extech offers LoZ dual impedance multimeters to address the problem. Two of our favorites are the EX355 and the EX655.

The EX355 is a professional True RMS digital multimeter which, on top of featuring the LoZ function, has a Low Pass Filter for use on variable frequency drive signals, a built-in NCV detector, 6000 count backlight LCD display, Data Hold, Min/Max, Auto Power Off and Relative Modes. The EX355 is capable of testing AC/DC Voltage, AC/DC Current, Resistance, Capacitance, Frequency, Type-K Temperature, Duty Cycle, Diode Test, Continuity. UL and CE certified with a CAT III 600V safety rating and a three-year warranty. See more of the EX355 and find out where to buy here.

The EX655 is a True RMS 600A Clamp meter which measures AC/DC Voltage, AC/DC Current, AC/DC microAmp Current, Resistance, Capacitance, Frequency, Type-K Temperature, Diode Test, Continuity. This meter features a 1.18" (30mm) jaw size in order to accommodate conductors up to 350MCM, DC Zero, Data Hold, Min/Max, Relative function, Auto Power Off Modes, a 6000 count LCD display (with bargraph), an NCV detector, Low Pass Filter, In Rush mode for current surges during motor startups and, of course, Low Impedance LoZ mode for ghost voltages. See more info for the EX655 and where to buy here!