Photographgraph of a mini digital multimeter in use by the authorHow to use Digital Multi Meters, DMMs & VOMs Safely

  • DMMs VOMs SAFE USE OF - CONTENTS: Safe Use of Electrical Test Equipment: DMMs & VOMs. How to Testdigital volt meter DMM or Volt Ohm Meter VOM meter condition. Electrical Inspection techniques Using DMMs and VOMs. How to use a digital volt meter safely using DMMs and VOMs Safely. Safety Warnings for Electrical Inspectors & Home Inspectors Using Electrical Test Equipment on Building Electrical Systems & Devices
  • POST a QUESTION or READ FAQs about safety procedures when using a DMM or digital multimeter

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DMM - digital multimeter safety:

This article discusses safety procedures to follow when using digital multi meters or DMMs or VOMs. We describe safety procedures for inspecting residential electric panels and building wiring using DMMs, volt meters, VOMs, and similar electrical test equipment.

These DMM/VOM safety procedures aid in addressing safety hazards found at residential electrical panels and electrical wiring systems and are intended for the electrical inspector, home inspector, or other professionals who examine residential electrical systems.

Safe electrical inspection procedures and safe use of volt meters, DMMs, multimeters, and similar electrical test equipment are discussed. Original text: DF, as ASHI Technical Journal Staff, January 1992, with updates through 2012.

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Safe Use of Electrical Test Equipment: DMMs & VOMs

Jensen analog VOM used by the author (C) Daniel Friedman In some circumstances, when examining electrical panels, receptacles, or other electrical devices in a building, ASHI, CREIA, CAHI, or other home inspectors may elect to make current and voltage measurements.

For inspectors who elect to use these tools, make sure that the tools themselves do not become a source of damage, or injury.

The following tips are based on a short article by Leonard Ogden in CEE News.

Shown here is my little Jensen analog VOM (volt ohm meter) which has served flawlessly for decades. At the top of this page is our still smaller pocket digital DMM DM78 made by CircuitMate™. Other examples of VOMs and ammeters or current measuring instruments are shown below.

How to Test digital volt meter DMM or Volt Ohm Meter VOM meter condition

High energy measurement instruments: Use only DMM's (digital multi meters) or VOMs (volt-ohm meters, the analog predecessors to DMMs) designed for high energy measurements.

Frequently check for damage to the meter itself, or for loose, cut, or worn test leads. If you can see the conductor in the leads, replace them. Check that there is low resistance between the leads themselves - a partial indication of good condition.

Use well insulated test leads that have finger guards.

Sperry Digisnap clamp on ammeter digital VOM measuring current draw at a furnace (C) Daniel Friedman

Insulate yourself from possibly live electrical parts by careful selection of clothing, leather boots, and where appropriate, insulated gloves.

Wear gloves: If you cannot operate your equipment while wearing gloves you have a safety problem. (Photo at left).

Use the proper voltage range and other control settings on the meter.

If you attempt a voltage measurements with test leads in the amps or current jack (a big but common mistake) and if your probes or meter are not fused, the resulting short across the voltage source can cause an explosion in the meter.

The photo (left) shows our Sperry Digisnap™ DSA-500 clamp-on ammeter that also functions as a digital VOM multimeter and continuity tester. Here, missing safety gloves, the DMM user was measuring 0.11 Amps current draw at a control on a gas-fired warm air furnace.

The openings at the bottom of the meter show that before attempting a current (amps) measurement the user removed the test leads from the instrument.

Don't use a DMM or VOM meter having cracked or loose parts. In selecting a meter, look for recessed input jacks to reduce shock risks at the connectors.

A simple volt ohm meter (VOM) such as the TriplettTM 310 shown here can be used to test for unexpected and unsafe voltage at a component. Set the VOM in the highest AC-voltage range.

One probe of the VOM is used to contact the surface of the electric panel (or any component to be examined), the other probe is touched to a reliable ground source,

[NOTE: Once having tested at the highest voltage range, greater accuracy may be obtained by choosing more sensitive ranges which permit readings to be taken in the upper portion of the scale.

Disconnect the test probes (or shut off the voltage source) before changing the voltage range setting on the VOM.] or in the example shown, to the neutral side of the circuit.

For example, if the VOM meter indicates more than 1or 2 volts between a service panel cover and ground, there's a safety problem.

Most low-cost analog-type meters such as the one described provide additional ranges used to read lower voltages with more sensitivity.

Some VOM models provide alligator clips for the ends of the test probes. These clips permit measuring high voltage without handling the probes. Always shut off the power before connecting the alligator clips.

Photographgraph of a Triplett clamp-on ammeter

This clamp-on multimeter made by TriplettTM can measure amperage draw (we used it when servicing and testing air conditioning system compressors) but it also includes probes permitting the device to be used as a standard, if slightly awkward probing VOM as well.

One feature we liked on this analog meter was the adjustable scale which permits measuring voltages in ranges of 1-5 volts, 5-25 volts, 25 to 125 volts, 100 60 500 volts (our scale for inspecting residential electrical equipment), high voltages from 250V up to 1250 volts, and as well, an ohms scale - making this a versatile analog multimeter.

After nearly 20 years we still make occasional use of this nice analog meter. Here's close up of the adjustable scale On this meter.


Electrical Inspection techniques Using DMMs and VOMs

Amp measurements using voltage clamps avoid extra risks of having to handle live wires. [See sketch at left.]

To measure amps or current see AMPS MEASUREMENT METHODS.

Also see DMM DIGITAL MULTIMETER HOW TO USE for the proper DMM or VOM function and range settings.

When measuring amps without a current clamp, make sure power is off before connecting into the circuit.

When disconnecting the multimeter or voltmeter, always unplug the red (hot) lead first.



Safe Use of Electrical Test Equipment: DMMs & VOMs

8.3 During an electrical system inspection the inspector is NOT required to
8.3.A. insert any tool, probe, or testing device inside the panels

Do Not Grab an Shake SEC Entry Mains in the Panel

In his final electrical seminar in St. Louis a decade ago, Bob Smith, a lecturer from SHRC, the Small Homes Research Council, told ASHI home inspectors and candidates that he always verifies the quality of the service connection at the main breaker by grabbing the two hot entrance wires and giving them and the panel a good shake.

Watch out: Don't do this! Readers would not be warned here if this questionable advice had not been presented at that seminar. Electricians and trained experts work with live electrical wires. Home inspectors should not do so.

October 22, 1988 - El Cajon, CA - a young electrician died when he accidentally electrocuted himself. Acting police Lt. Carl Case said 19-year-old Sean M. Smith was working under a house, lying on his back working on an electrical addition to the house, when his wire [strippers] accidentally connected with a live wire. He said Smith's boss, Troy Beatty, heard the victim yell. Beatty found Smith unconscious under the house, pulled him out, performed CPR, and summoned help. -- IAEI News, November/December 1990 p.40.

These electrical inspection suggestions are not a complete inventory of all electrical components that should be inspected; these notes focus on identification of conditions that may present special electrical hazards for the electrical inspector.

Contact Us by email to suggest changes, corrections, and additions to this material.

ELECTRICAL INSPECTOR SAFETY PROCEDURES describes important basic safety procedures, clothing, gloves, eye protection, and other safety equipment for home inspectors and electrical inspectors.

Safety Warnings for Electrical Inspectors & Home Inspectors Using Electrical Test Equipment on Building Electrical Systems & Devices

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. 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.

Simpson Instruments adds the following safety advice for users of VOMs and DMMs and similar test devices, and other instrument manufacturers offer similar cautions: [6]

Fluke adds this safety advice: To avoid possible electric shock or personal injury, follow these guidelines: [5]

Additional Advice to Avoid Damaging VOM or DMM & Equipment

Fluke adds this advice: To avoid possible damage to the Meter or to the equipment under test, follow these guidelines: [5]


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