Working with electricity can be dangerous or even lethal. Knowing what is hot and what is not differentiates a safe worker from a risk taker who doesn't bother to find out ahead of time.
Electricians in the field should have proper test instruments on hand all the time and know when and how to use each testing tool. When not using appropriately rated meters, the electrician always faces the danger of getting injured.
Meter products are covered by International Electrotechnical Commission (IEC) standards and many are Underwriters Laboratories (UL) stamped. The UL, itself, follows the IEC standards, which are designed to protect users from unknown voltage and accidental misuse.
The standards for meters for CAT I (electronic and low energy equipment), CAT II (appliances, PCs, TVs and all outlets more than 30 feet from a Cat III source), and CAT III (motor control panels, including feeders and short branch circuits, distribution panel devices, and heavy appliance outlets) are already in place.
Most of today's meters are safer than yesteryear's meters. So, even if you don't need more meters, perhaps you should update to safer ones. Even the meter casings, today, are far more fire retardant than dated ones.
Once CAT IV standards are approved, they will become the standards at the primary supply level, for measuring outdoor equipment and service entrance equipment, and will cover exterior transformers and meters, such as service drops from pole to building, overhead lines to detached buildings, and underground lines to well pump.
What to look for when buying test equipment
You can get many more features, and therefore greater job efficiency, in the same size product at a lower price than in the past. Many new meters are digital; some combine digital with analog on the same screen. The increasingly popular digital meter-minus a moving needle that can break-is more rugged and less prone to damage than an analog meter, which must be recalibrated if dropped. However, the liquid crystal display (LCD) on a digital meter won't work at or below freezing temperatures, because the liquid in the LCD gets too thick. At the other extreme, the liquid gets too thin and turns black at very high temperatures.
Many electricians still use analog meters either from habit or because they feel they can get information from a moving needle that they cannot get from a digital meter, such as looking at trends and variations. (Some electricians, for example, apply tape to mark a range they are working with and then can just glance at the meter and see if the needle is still within range.)
When selecting new equipment, make sure the devices you are buying display a category rating-for example CAT III, 600 volts. Look for UL approval, added safety features, a good quality feel, whether or not it is fire retardant and "ruggedized" (i.e., certified to have passed a UL impact test), a generous warranty and service policy, and apparent ease of use. You may have to pick and choose those features that are most important to you.
True RMS versus average responding
For measurements taken with digital multimeters and clamp-on meters, true RMS (root mean squared) is useful for measuring non-linear loads such as variable speed drives, electronic lighting ballasts, computers-anything that draws current in a pulse.
Residential contractors would likely be satisfied with an average responding reading when testing voltage, resistance, and continuity, because they are not likely to encounter harmonics problems. In commercial and industrial environments, however, large non-linear loads can cause harmonics, which distort the waveform and could affect the validity of the reading given by average responding meters.
Average responding meters always assume measurement is of clean sine waves and, if that is not the case, readings can be off by up to 40 percent. In some circumstances, an electrician would likely want the true RMS feature, which uses internal circuitry to give a highly accurate value regardless of the current or voltage wave shape.
Interface with computers
Some manufacturers offer software and interface cables that work with their meters to expedite data recording and analysis. Electrical contractors with clients who demand reports and hard data, especially in justification of renovation or repair work, might well appreciate the added functionality of software-enabled meter-to-computer communication.
Proper setup of manufacturer-supplied software allows an electrician to walk a job, taking readings, or to set up a meter to take automatic readings at a designated time frequency. Then, the electrician can download those readings into a spreadsheet or word processing application for printout or analysis. The software can, for example, display minimum/maximum or average readings, charted over time, or it can create a log. The program might analyze voltage and current, and, in some cases, monitor resistance.
Workhorses: Voltage testers, clamp-on meters, and multimeters
A basic voltage tester is useful for determining if a circuit is live, and its approximate voltage if it is, before an electrician works on it. Analog voltage testers, equipped with plungers, are not as accurate as digital voltage testers. Digital multimeters, in some cases, include additional features such as data hold, resistance measurement, continuity testing, ground fault circuit interrupter (GFCI) testing, and phase-sequence indication.
Representative voltage testers
ETCON VT 154 Audible Voltage/Continuity tester and the IDEAL 61-076 Vol-Con voltage continuity tester are analog vibration voltage indicators offering positive AC/DC voltage identification, vibrating when voltage is present.
The Fluke T2 Voltage and Continuity Tester uses digital circuitry and light-emitting diodes (LEDs), to indicate AC/DC voltage levels.
The small-size Amprobe KWIK-I-E model K-1 Volt/Amp Probe offers one-handed non-contact measurements. Featuring a bar graph display, it gives an appropriate level of voltage and amps without any wires (AC current up to 60 amps and AC voltage up to 600 volts).
The IDEAL digital 61-401 Test-Pro Stick Multimeter offers five interchangeable snap-on heads providing a diversity of capabilities, including a true RMS head, an infrared temperature head with a 4:1 angle of viewability, and a current clamp, which requires no conversions or multipliers. The stick case, which is slim enough for one-handed operation, is designed to absorb the impact of a 10-foot drop.
The Greenlee digital DVC-10 has a GFCI and continuity testing capability, which makes additional testers unnecessary. It comes with a dual display consisting of a nine-LED display and a LCD screen. The DVC also offers a wide measurement range of up to 700 volts and amps for AC and DC readings. The unit comes with a built-in super-bright flashlight for probe positioning in dark areas.
Clamp-on meters measure electrical current on electrical machinery, wires and cables without interrupting the circuit, by sensing the magnetic field around the conductor. The larger the current the greater the magnetic field; the meter translates the field into an amperage reading. Clamp meters can measure up to, and even above, 2,500 amps safely. The maximum current is determined by the size of the jaw-a larger jaw will fit around larger amperage conductors. As a rule of thumb, clamp meters are good for one amp or greater while multimeters are used for measuring milli-amps.
In addition to testing AC current, some digital models also test DC current. Specific features on individual models vary by manufacturers or even within manufacturers. You may find various combinations of possibly desirable features, such as maximum (or peak) hold in addition to the display hold; true RMS ratings for AC current; an analog output signal on a digital model, voltage and resistance.
Some clamp-on meters have recording capabilities, with optional interface cable and software for downloading of data to computers. Other possible features include auto ranging, and measurement of frequency, peak or in rush current, and temperature. Various manufacturers (though a dwindling number) also continue to offer analog clamp-on meters that will do dual measuring (AC and DC), as well.
By browsing catalogs or talking to manufacturer representatives, it should be easy enough to hone in on a clamp meter that has the combination of features you want. For example, the Amprobe AC/DC 3000 digital clamp-on meter, with an adjustable display that can show 3 3/4- or 4 1/2-digit 4,000/20,000 counts, offers peak hold (with maximum and minimum recorded), and captures spike, glitches, motor run, and start currents (AC or DC). The unit measures AC/DC true RMS for AC current to 1,000 amps and AC/DC true RMS voltage to 600 volts. It offers both auto and manual ranging.
The Greenlee CM-1200, offering True RMS readings on a 4,000-count LCD panel, has AC/DC measurement capability up to 1,000 volts and 1,000 amps. Equipped with large jaws to handle heavy gauge cables, it also has peak hold.
The Hioki 3282 Digital Clamp-on HiTESTER provides true RMS readings and offers peak value along with crest factor waveform distortion display (peak value/RMS value). The unit measures up to 1,000A AC in conductors up to 46 mm diameter. With an optional probe, users can also measure temperature.
AVO DCM R series digital clamp-on multimeter, providing true RMS AC/DC readings, has a barrier that indicates to the operator a safe working distance for the user's hand to be from live uninsulated conductors. The units have auto ranging and auto zeroing, an LCD display, and peak hold capability.
The IDEAL 61-726 Digital Clamp Meter offers 1000A AC/DC, true RMS, capacitance, and peak hold, while the IDEAL 61-711 analog clamp meter offers 600A AC, pointer lock, and a broad frequency response (50-400Hz).
The UEi DL49 clamp multimeter, measuring both AC and DC inductive current in addition to voltage and resistance, sports an offset clamp arrangement.
The Fluke T5 voltage continuity and current tester offers a two-fork meter that features two fixed prongs, rather than the curved clamp. Sporting a continuity beeper and detachable probe tips, the device is available in 600V and 1000V models. The "OpenJaw" circuit lets users check current up to 100A without breaking the circuit. The compact design, notes the company, makes the meter, which measures both AC and DC volts and AC (open jaw) current, easier to maneuver into tight locations and less bulky on the tool belt.
A digital multimeter (DMM) allows an electrician to take accurate voltage measurements and testing of resistance and continuity, as well as testing of small current. Though digital multimeters can read current, they are fused at 20 amps or less for safety because the meter is connected in series, and higher amperage could pose danger to the user. You can use a clamp-on adapter, to measure current safely but the accuracy is not as great as with a dedicated clamp-on meter. For someone who already owns a DMM, this is an inexpensive way to add current reading capability safely to the mix.
Many hand-held multimeters come with two test leads but you can get units with built-in extended test probes (enabling safer two-hand usage). Options from various manufacturers include accessories for current measurement, true RMS, and infrared temperature.
The IDEAL 61-361 Test-Pro Contractor DMM, for example, housed in a sturdy case with protective rubber boot, measures three-phase motor rotation (up to 480V), capacitance, and frequency. The unit, which comes with overload protection on all ranges and a sleep mode, is compatible with an optional snap-on head for a 300A AC current clamp and deluxe test leads.
The Yokogawa DMM733 Series of digital multimeters features shutters that are interlocked with the function switch to prevent erroneous insertion of test leads. The units, which have auto hold, sport a withstand current fuse with high breaking current for current measurements that is designed to prevent explosions and discharge especially during current measurements.
The Greenlee DM-820 S-Series Voltage Tester digital multimeter has record maximum, minimum, maximum-minimum, and average readings and data hold, crest capture (5ms peak hold) maximum, minimum, and maximum-minimum readings, true RMS, auto ranging, and a 52-segment analog bar graph display capability to view quick changes. A temperature probe measures up to 1,832 degrees Fahrenheit. The DM-820 is, according to the manufacturer, the only one of its kind that complies with the proposed Cat IV standards. The device works with optional Win95/98 software and RS 232 cable, for retrieval and display of stored data and real-time data logging and graphing. The data can also be exported to disk for analysis with any spreadsheet.
The Fluke 89 Series IV is a true RMS digital multimeter with a minimum-maximum record feature that captures peaks as short as 250 microseconds. The meter has a hold function that can be activated manually or automatically off of the input signal. In addition to the 51-segment bar graph, the meter sports a dual display where DC and AC measurements or AC voltage and frequency component of a signal can be displayed simultaneously. The built-in memory can store readings along with time stamp, or log up to 1,000 interval readings of minimum, maximum, and average values. Using the built-in IR communications link and optional FlukeView Forms software, meter data can be transferred to a PC for analysis and documentation.
Hioki 3801-02 true RMS DIGITAL Hi-TESTERS, with a full range of functions, also support data collection on PCs with the addition of the optional 3852 RS-232C package.
Portable insulation testers
A megohmmeter measures conductor insulation resistance in cables and motors. The megohmmeter, with digital or analog readout, may be electronic, motorized or manual, requiring hand cranking. The megohmmeter applies a relatively high voltage to the circuit under testing and looks for current flow. If the insulation is good, the meter shows a steady increase in resistance. If the insulation is poor, the resistance will remain low and current will flow.
In industrial facilities, maintenance testing of motor windings (to test for shorts or weak windings and to show how strong the insulation is between the windings), and cables exposed to harsh environments (including dirt, grime, moisture, abrasion, all of which cause insulation deterioration and affect the integrity of the wire) is performed on a regular basis. When a performance drop is seen over time, scheduled maintenance can be planned before the unit causes a production failure. Insulation testers are used frequently, perhaps monthly, for predictive maintenance. Because high voltage stresses conductors, it is usually not done more frequently.
Megohmeters are also used to test feeders in new facility installations before the conductors are connected to switchgear. The stress of pulling feeders can damage the wires, which in turn could damage the switchgear. The manufacturer specifies a test voltage for the wire to test integrity of insulation. When a large test voltage is applied, the meter checks for voltage leaks through possible breaks in the insulation, even as small as a pinhole. Similarly, motors are often tested after servicing to ensure there is good isolation between windings and between windings and the frame.
The Megger DET5/4D and DET5/4R (AVO International), for example, is a digital tester suitable for testing of ground electrodes and measuring ground resistance. Housed in a rugged water-resistant case, it can be used indoors or out (to test the integrity of the soil) on both simple and complex electrode systems.
Greenlee offers a digital/analog megohmmeter, 5878, which provides auto ranging AC/DC default voltmeter and warnings, and tests three voltage ranges up to 1,000V. Housed in a rugged cabinet that is resistant to weather, water, and dust, it also features an auto power off to extend battery life. An optional remote-control test probe with flashlight function is available. The company also offers a manual-crank analog megohmmeter 5778 that provides nondestructive insulation testing of three voltage ranges up to 1,000V DC) suitable for machines, equipment, transformers and electric motors.
AEMC 1045 Digital/Analog Megohmmmeter, with large multifunction display, shows both the 4,000-count digital display and an arced analog bar graph for readings for capacitive charge and absorption trend characteristics. The unit, which has a remote test probe, will beep automatically at 30-second, 60-second, and 10-minute intervals to remind the user to record the measurement.
The digital AMB-5D megohmmeter from Amprobe features an 80 mm x 50 mm LCD panel with 50 segments analog display (maximum reading 4,000 M ohms), with both readouts visible simultaneously. An over-range indication is displayed on the LCD panel when an out-of-range measurement is made.
IDEAL 61-786 is an analog insulation tester that sports a live circuit indicator, display light, multicolor scales, remote control test probes, and guard terminal.
HIOKI Model 3453 DIGITAL M? HiTESTER offers four selectable insulation measurement load voltage ranges of 125, 250, 500, and 1,000V. In addition to the LED readout, it has a logarithmic scale bar graph display from zero to 4,000M ohms, providing the feel of an analog meter.
The equipment for Infrared (IR) testing is less costly than it used to be, making it a hot technology item among electricians. Without an electrician having to disconnect the breaker or remove the panel cover, an IR thermometer (or sometimes a "gun") tests to determine whether a breaker is going to fail before it actually fails. As breakers age, they become more resistive, throwing off more heat. The testing procedure is to run an IR thermometer down a panel quickly and see if there are any breakers that are overly hot.
This form of preventive maintenance test is suitable for critical loads in a commercial or industrial setting, where failure of critical machinery can interrupt workflow. IR test equipment also tests for loose connections or to determine if phases are overloaded.
Typically, the test is looking for a heat rise above ambient. If an electrician does an infrared scan and the reading is much higher than expected, depending upon findings, the electrician has to change the breaker or re-distribute the load on the phases, to prevent fires, overheated neutrals, and explosions.
When differentiating among IR testers for your needs, take note that the angle of viewability can range from 6:1 to 32:1, with the higher ratio being more costly. The greater the angle of viewability, the more focused your measuring area is. For measuring circuit breakers a 6:1 angle of viewability generally suffices. Units with a laser pointer provide easy pinpoint location, for accurate aiming.
Fluke, IDEAL, and Greenlee, for example, offer handheld thermometers with laser targeting and LCD readouts. The Fluke 65 has min/max, temperature memory and auto sleep mode. The IDEAL 61-682, with a 15:1 angle of viewability, also has a sleep mode and measures temperatures between 0 degrees F and 500 degrees F. The Greenlee THH-500 has a 6:1 angle of viewability and can read a four-inch spot at two feet.
Gas tube testers
Tube testers provide a range of tests to locate problems within a fixture, honing in on whether the problem lies with the lamp, the ballast, the starter of the resistor, without having to remove the lamp or open the fixture to check the ballast. Typically a lamp tester, such as the Greenlee LT-100 and the ETCOM LT-130, can handle many types of bulbs, including fluorescent, low-pressure sodium, high-pressure sodium, neon, mercury, and metal halide.
Cable tracers are hand-held devices that help electricians safely and speedily determine which breaker protects a given outlet, without disturbing the service. The electrician plugs a small transmitter into an outlet at the location in question and then retreats to the panelboard. At the panelboard, the electrician passes the locator up and down in front of the breakers. The locator picks up the signal sent out by the transmitter when over the appropriate breaker. Cable tracers can also eliminate manual ringing of circuits in new installations.
The UEi CBF100 Circuit Breaker Finder incorporates microprocessor technology to pinpoint a specific circuit breaker in a panel. Once the transmitter is plugged into a live wall receptacle, the device automatically adjusts range and sensitivity, using an automated sensor to locate the correct panel and breaker.
IDEAL 61-052 Circuit Breaker Finder will also automatically identify circuit breakers and fuses without service interruption, using a plug-in transmitter and hand-held receiver with adjustable sensitivity level. The device offers both visual and audible indicators.
Amprobe BT-100 Break'r Trac'r is designed specifically for residential applications, offering an audible tone and LED display to confirm breaker identification when identifying the 120V AC circuit breaker or fuse supplying a particular receptacle or lighting fixture.
Three-phase motor rotation tester
Three-phase motor rotation testers are very popular with electricians wiring three-phase 277-, 480-, and 600-volt motors. Motors run more efficiently and draw less amperage on three-phase power, but since the units are hooked up with three hot leads, it can be difficult to determine which leads to put on for proper rotation. (If the leads are hooked up in an inappropriate combination the motor will run backwards.) The tester reveals how to connect the leads for proper rotation.
Greenlee 5123 motor rotation indicator sports three color-coded wired leads with heavy-duty alligator clip and bright red and green LEDs to indicate rotation of motor. IDEAL 61-520 also has color-coded insulators over alligator clips and sequential directional light indicators.
For GFCI diagnostics, Leviton offers a specialized GFCI Circuit Tester 6185. The tester is used to confirm that a GFCI is wired for proper operation and that it trips at the required threshold for ground fault circuit. The device plugs into an installed GFCI receptacle and provides a four-position dial for administering circuit polarity and trip test functions, along with indicator lights. The unit can also be used for ensuring that installed GFCIs comply with OSHA requirements for the Assured Equipment Grounding Conductor Program.
IDEAL 61-051 E-Z Check Plus GFCI Circuit Tester identifies correct wiring, open ground, reverse polarity, open hot, open neutral, hot on neutral, hot and ground reversed with open hot and ground fault interruption. The IDEAL 61-152 SureTest Circuit Analyzer performs additional functions such as measureing voltage drops and ground impedance, and verifies isolated grounds.
The Greenlee 5708I Inspector GFCI and Circuit tester has LED indicators to signal correct wiring, open ground, open neutral, open hot, hot/ground reversed, and hot/neutral reversed. The unit indicates whether a GFCI will trip at 3,5,7 or 10mA.
Companies mentioned in this article:
AEMC Instruments, www.aemc.com, (800) 343-1391
Amprobe, www.amprobe.com, (800) 477-8658
AVO International, www.avointl.com, (800) 723-2861
Etcon Corp. www.etcom.com, (800) 367-4119
Fluke, www.fluke.com, (800) 44-FLUKE
Greenlee/Textron, www.greenlee.textron.com, (800) 435-0786
HIOKI E.E. Corp., www.hioki.co.jp, (609) 409-9109
IDEAL Industries, Inc. www.IDEALindustries.com, (877) 201-9005
Leviton, www.leviton.com, (800) 323-8920
UEi (Universal Enterprises, Inc.), www.ueitest.com, (800) 547-5740
Yokogawa M&C Corp., www.yokogawa.co.jp, (800) 888-6400
The FELDMANS write on trends and products, including computers and electronic commerce technologies, for the electrical and general contracting fields. Authors of Construction & Computers (McGraw-Hill), they can be reached at firstname.lastname@example.org or at (914) 238-6272.