How to use Digital Multi Meters or DMMs Safely InspectAPedia® -
Safety During Electrical System Inspections
Using DMMs and VOMs Safely
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This article discusses How to use Digital Multi Meters or DMMs Safely - Safety Procedures for Inspecting Residential Electric Panels, volt meters, VOMs, electrical test equipment. This is a chapter of our electrical safety procedures article discusses safety hazards at residential electrical panels and suggests safety procedures 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.
Safe Use of Electrical Test Equipment: DMMs & VOMs
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.
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.
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 we were 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 we removed the test leads from the instrument.
Don't use a 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.
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.]
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. 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.
General Electrical Safety Suggestions describes important basic safety procedures, clothing, gloves, eye protection, and other safety equipment for home inspectors and electrical inspectors.
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Additional technical contributors & reference sources for this article are listed below.
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"Frequency of Occurrence and Sources of Rust and Corrosion in Electrical Panels," Daniel Friedman, IEEE HOLM Conference, Philadelphia PA, 1992 - see ELECTRIC PANEL RUST for an online version of this article.
Jim Simmons: Personal communication, J. Simmons to Daniel Friedman, 9/19/2008. Photographs contributed to this website by Jim P. Simmons, Licensed Electrician, 360-705-4225 Mr. Electric, Licensed Master Electrician, Olympia, Washington Contact Jim P. Simmons, Licensed Master Electrician, Mr. Electric, 1320 Dayton Street SE
Olympia, WA 98501, Ph 360-705-4225, Fx 360-705-0130 mrelectricoly@msn.com
Kenneth Kruger: Original author of the sidebar on testing VOM DMM condition: Kenneth Kruger, R.A., P.E. AIA ASCE, is an ASHI
Member and ASHI Director in Cambridge, MA. He provided basis for this article penned by DJ Friedman.
"How to Use DMM's Safely," Leonard Ogden, CEE News, 888 Seventh Ave., New York, NY 10106, Dec 1990 p.10.
Dr. Jess Aronstein, consulting engineer, Poughkeepsie NY, 1991 protune@aol.com
Rex Cauldwell, master electrician and contributor to the Journal of Light Construction on electrical topics
New York State Central Hudson Gas and Electric Company, G&E/1-2/85 consumer safety pamphlet
American Society of Home Inspectors, ASHI Training Manual, Al Alk -[obsolete, and includes unsafe practices-DF]
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
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Recommended books on electrical inspection, electrical wiring, electrical problem diagnosis, and electrical repair can be found in the Electrical Books section of the InspectAPedia Bookstore. (courtesy of Amazon.com)
Aluminum Wiring Information WebsiteAluminum Electrical Wiring Hazards and Repairs: in-depth authoritative info, photos, documents including selection of proper vs. ineffective repair methods. E.g.: Ideal 65 "Twister" purple connector fails in field and lab testing with aluminum wire.
Circuit Breaker, a bad one fails to trip failure at aluminum bus-to-circuit breaker connection - field report and photographs
Electrical Panels, How to Inspect in Buildings, safety for electrical inspectors, electrical panel, fusing, wiring defects, defective products. Inspection Class Presentation
Federal Pacific Electric (FPE) Stab-Lok Circuit Breaker Panel Hazards Website - Latent fire hazards, in-depth authoritative research, documents, advice on Stab-Lok electric panel and circuit breaker failures and what to do when this equipment is found in buildings.
"Electrical System Inspection Basics," Richard C. Wolcott, ASHI 8th Annual Education Conference, Boston 1985.
"Simplified Electrical Wiring," Sears, Roebuck and Co., 15705 (F5428) Rev. 4-77 1977 [Lots of sketches of older-type service panels.]
"How to plan and install electric wiring for homes, farms, garages, shops," Montgomery Ward Co., 83-850.
"Electrical System Inspection Basics," Richard C. Wolcott, ASHI 8th Annual Education Conference, Boston 1985.
"Simplified Electrical Wiring," Sears, Roebuck and Co., 15705 (F5428) Rev. 4-77 1977 [Lots of sketches of older-type service panels.]
"How to plan and install electric wiring for homes, farms, garages, shops," Montgomery Ward Co., 83-850.
"Home Wiring Inspection," Roswell W. Ard, Rodale's New Shelter, July/August, 1985 p. 35-40.
"Evaluating Wiring in Older Minnesota Homes," Agricultural Extension Service, University of Minnesota, St. Paul, Minnesota 55108.
"Electrical Systems," A Training Manual for Home Inspectors, Alfred L. Alk, American Society of Home Inspectors (ASHI), 1987, available from ASHI. [DF NOTE: I do NOT recommend this obsolete publication, though it was cited in the original Journal article as it contains unsafe inaccuracies]
"Basic Housing Inspection," US DHEW, S352.75 U48, p.144, out of print, but is available in most state libraries.
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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.
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