VOM in use measuring live voltage (C) Daniel Friedman Devices Used to to Detect or Measure Voltage
Choices of Devices used to Detect or Measure Electrical Voltage at / in a Building

  • VOLTS / AMPS MEASUREMENT EQUIP - CONTENTS: Voltage Measurement Equipment Types: photographs & properties of electrical test equipment useful for a building inspector, electrical inspector, contractor, or homeowner: Greenlee® GT-16 adjustable voltage detector, Tic Tracer Tif 300cc voltage detector, clamp-on or snap-around ammeter or digital multimeter properties & applications. WHERE TO BUY - List of Electrical Test Instruments, VOMs, DMMs, Voltage Detectors: Manufacturers & Sources
  • POST a QUESTION or READ FAQs about how to detect or measure voltage at electrical wiring or electrical devices.
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Electrical voltage detection and measurement methods & tools:

This article describes the range of equipment or tool choices used to detect or measure voltage and other electrical values.

We describe the use of digital multimeters(DMMs), Volt-ohm meters (VOMs), neon testers and other types of voltage detectors used to check for the presence of voltage, to check for live electrical circuits and to measure electrical system voltage and amperage levels.

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Voltage Test Equipment Types: How to Determine Electrical Voltage (240V/120V) using a neon tester, a VOM, DMM, Volt Meter, or Voltage Detector pen

Neon Tester

Instruments as simple as the neon-tester shown here or a digital multimeter (DMM), or an analog volt meter (volt-ohm meter or VOM) such as those made by Triplett, Fluke, Simpson and Sperry can be used to measure the voltage level between the two power feed lines to confirm the presence of 240 Volt service. (Some versions of this equipment can also be configured to measure amperage or amps).

Using a DMM, A VOM -analog volt meter, or a neon tester, voltage between the two apparently "hot" wires in the panel will confirm 240-volt service. If only one cable is "hot" (testing cable to ground) it is a 120 V system. If both cables are "hot" to ground but there is no voltage between them it is a 120V system which has been "split" to look like 240V but it is not 240V.

What's the difference between using a neon tester (shown at left) and using a VOM or digital voltage meter?

A neon tester, containing just a light bulb, simply indicates the presence of live voltage but not the actual voltage level. A volt meter is required to test for other voltage levels or to determine the actual voltage level as well as to check for voltage that may vary over time.

Watch out: this is not a reliable nor a complete electrical system test. For example, a weakly-grounded wire or electrode may look just fine when tested with a VOM, a DMM, or a neon tester, but when subject to higher current flow the ground may be completely inadequate.

Safety Warning: The ASHI Standards of Practice and other home inspection standards for electrical inspections do not require the inspector to insert any instrument into the service panel. Therefore this testing is optional. It's also a dangerous procedure that can damage electrical equipment or worse, cause electrical shock, or even death, and should not be undertaken unless the person conducting the examination is trained and competent to avoid electric shock.

Using a neon tester to check for power at electrical wires (C) Daniel Friedman

A detailed example of safe use of a neon tester to check for voltage is at REPAIR AUTOMATIC OUTDOOR LIGHT FIXTURE.

If the inspector is not trained for this procedure s/he should never insert any instrument or tool into electrical equipment.
See SAFETY for ELECTRICAL INSPECTORS at Residential Electric Panels.

Definitions of Common Electrical Test Meter Types

Multimeter combined with ammeter (C) Daniel Friedman

Simpson VOM Model 260 Series III ca 1958 (C) D Friedman Paul Galow

Voltage measurement precision vs accuracy (C) Daniel Friedman

In this article we provide photographs and descriptions of each of these types of electrical test instruments.

Photographs & properties of electrical test equipment useful for a building inspector, electrical inspector, contractor, or homeowner

If you're unsure about the definitions of amps, volts, ohms, resistance, watts, etc.

Greenlee GT-16 adjustable voltage detector (C) Daniel Friedman

A voltage detector of voltage sensor detects the presence of live AC voltage (some equipment also detects DC voltage), with a sensitivity typically between 5 and 1000 Volts. This equipment can sense the presence of live electrical devices or wiring without touching the device or wire.

Shown here (left) is the Greenlee® GT-16 adjustable voltage detector. Greenlee and other manufacturers recommend that you test the operation of the voltage detector on a known live circuit both before and after using it to test for the presence of electrical voltage at a wire or device.

This device uses an AAA battery and has a sensitivity adjustment (the yellow dial in the center of the green patch on the device).

Some voltage sensors such as the FCB Voltage Pen operate without requiring a battery.
Greenlee GT-16 adjustable voltage detector (C) Daniel Friedman

Tic Tracer Tif 300cc voltage detector - properties & special uses: A different sort of voltage sensor detects the presence of live AC voltage is shown at left, the Tif 300cc Tic Tracer.

Depending on the version, this instrument does not use an LED or neon bulb but emits a buzzing or "ticking" noise at a varying rate depending on how close it is held to a voltage source and also varying by voltage level.

Turning the instrument on gives a slow electronic tic-tic sound at a regular rate. Holding the sensor tip close to an electrical outlet or even along an electrical wire connected to such a receptacle results in an increase in the tic rate of the instrument.

And with even a limited amount of practice you can quickly learn to recognize the much faster tic rate (really a buzz) that the TIF makes when held close to a 240V circuit in comparison with a 120V electrical circuit.

Greenlee GT-16 adjustable voltage detector (C) Daniel Friedman

Unlike the elegantly simple neon tester, and more like the Greenlee® GT-16, the TIF Tic Tracer does not need direct contact between sensor pins and live electrical contacts in order to detect the presence of electrical voltage (photo, above left).

But unlike the Greenlee® GT-16 that needs to be very close to an electrical circuit or component in order to indicate the presence of voltage, the TIF Tic Tracer 300cc can sometimes detect the presence of electrical wires behind drywall (depending on the depth of wires inside the wall cavity and other factors) - as we illustrate in our second Tif 300cc photo, shown at left.

Watch out: the sensor tip of the Tif Tic Tracer is also sensitive to static electricity and possibly to vibration.

If you rapidly swipe the sensor tip along the surface of a wall the instrument will sound wildly - an effect we once used to castigate an aggressive bystander.

VOM in use measuring live voltage (C) Daniel Friedman


Analog VOMs - Volt-Ohm-Milliameters

Simpson VOM (C) Daniel Friedman

A VOM or volt-ohm meter may also be found in an analog form such as our favorite and now a collectors-item little Jensen VOM that we've used for nearly 30 years. Here our photo shows the Jensen analog VOM with its probes attached but not connected to anything.

In 30 years of use we needed one repair of this instrument - an internal fuse which we couldn't find locally. In analog VOMs such as this unit there is typically a very low-amperage fuse whose function is to protect the meter movement from damage.

This little VOM, ca 1985, is about 1/8 the size of the Simpson 260, ca 1958, described just below.

Simpson produces a wide range of test instruments including analog VOMs that can be used to measure resistance (ohms), direct current, alternating current, and even decibels.

See ANALOG VOMs & MULTIMETERS for examples of VOMs.


Amperage or current measurements using clamp on or snap around digital ammeters, DMMs, & (some) VOMs

A W Sperry Instruments Digisnap DSA-500 digital multimeter with snap around ammeter (C) Daniel Friedman

At above left we are measuring the current draw in amps for the charging block of a laptop computer. Shown is Sperry's Digisnap DSA-500 snap-around digital multimeter.

Details about using a clamp-on or snap around ammeter are at

Notice that the electrical wire was split so that the clamp-on ammeter's jaws surround just one of the two electrical wires. The transformer jaws or "clamp" must surround just one of the two 120V wires supplying the electrical device.

Also notice that we did not disturb nor damage the electrical wire insulation itself - doing so is dangerous and risks equipment damage or dangerous electrical shock as we cite just above.

At the moment of our measurement this electrical device was drawing 0.29A at 120V.

For an accurate calculation of actual energy consumed that includes the effects of AC current and power factors,
see DEFINITION of Power Factor, Real Power.

What about using a simple receptacle tester to measure voltage?

Receptacle and GFCI Test Procedure (C) Daniel Friedman

Receptacle testers are used by most home inspectors to check for proper wiring at electrical receptacles as well as to check the function of GFCI's.

For testing AFCI's the only reliable test currently available is the device's own test button. We provide details about using receptacle testers
at ELECTRICAL TOOLS Every Homeowner Should Have

Where to Buy a DMM or VOM
List of Electrical Test Instruments, VOMs, DMMs, Voltage Detectors: Manufacturers & Sources


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