For anyone who works on electrical components, there are certain must‐have, electricity‐101 tools that you’ll find in every tool box. In addition to all the hand tools that help you complete every repair or replacement properly, a big part of the job is related to testing and diagnostics. Let’s face it, electrical troubleshooting, more often than not, involves finding subtle variations on any number of operating factors that can point to a not so subtle problem.
When it comes to diagnostic work, a key weapon in the toolbox arsenal is a digital multimeter, or DMM. Depending on the multimeter, it can provide a digital readout of voltage (VDC and VAC) and current (A). More sophisticated models may also measure duty cycle (%), capacitance (nF), frequency (Hz), offer diode and continuity testing, and temperature readings via Type K (thermistors) probes.
The market is flooded with multimeters in a range of capabilities and prices. When you discount the ones that aren’t relevant for industrial electrical work, you’ll still find scores of handheld digital multimeters that could be a good fit for your needs as an electrical contractor. When it comes to choosing a new DMM, some electrical contractors shop “on autopilot” and they will only buy one brand. It could be nostalgia—“My father used the same brand.” Or some only buy American‐made. (On that last point, double‐check the label—you might be surprised to find a historically American DMM manufacturer actually making many multimeter models overseas now.) Some rely on the advice of colleagues in the business, or brands they first discovered as an apprentice or at a technical school.
How do you decide what’s the right model for you and your work? The best approach is to make an apples‐to‐apples comparison. What are the key factors to whittle down the list?
Make sure your choice satisfies five important conditions:
- Safety
- Accuracy
- Versatility
- Reliability
- Value
The goal of this article is to take a closer look at the numerous variables that go into satisfying the above five conditions.
1. Safety First
Did you know that electrocution ranks as one of the top five causes of death in construction sites? Even the most “Cool Hand Luke” electrical contractor cannot be too cool for electrical safety. To that end, your multimeter can often times be one of the few things separating you from a jolt that could be harmful or fatal. So, you’ll understand if we spend the most time on safety. Without it, you could be dead in the water—literally.
Third Party OK’s: The first thing to check is that it has the label of an independent verification lab such as UL, CSA, CE, ETL or TUV. Don’t touch it unless they say it’s okay. We also have the sage guidelines set forth by the IEC, the International Electrotechnical Commission. Their IEC 1010 overvoltage category definitions set explicit standards for what kinds of protection an electrician would receive from his multimeter.
The CAT’s Meow: You’ve seen these overvoltage categories before: CAT I CAT II, CAT III and CAT IV. But did you know what they really meant? The primary hazard we’re trying to protect ourselves from is an unexpected spike or transient of high voltage. (Well, aren’t they all unexpected?) A spike can come out of nowhere from a variety of electrical sources, whether it was a good old fashioned act of God—lightning—to the typical components you deal with every day: motors, variable speed drives, capacitors as well as power conditioning and conversion components.
If something is switching on and off up the line that you don’t know about, there could be a hazardous spike coming your way as well. There’s no radar for advance warning on these things; the best protection is whatever is standing between you and that spike—your multimeter and its test leads.
So, back to those categories. There are four categories defined by the IEC defined roughly as:
- Category I — generally electronics and equipment that is protected to control spikes
- Category II – single‐phase loads connected to an outlet or receptacle with a physical distance from a CAT III source of 30 feet or a CAT IV source 60 feet away
- Category III – three‐phase distribution covering most industrial plant assets and electrical connections and components, plus commercial lighting systems
- Category IV – generally outdoor installations with three‐phase connections coming “from the pole”
Bottom line is, the higher the CAT, the closer you are to a utility connection and the higher the risk for high power transients. (For more, take a look at the chart “Categories by the Numbers.”) So, when you are looking for a digital multimeter, you want to be sure that not only is it capable of measuring the max steady state voltage that you’ll typically encounter on the job, but also the ability to stop a spike in its tracks and prevent a potentially lethal arc flash.
Your safest bet is to purchase a durable CAT IV rated meter and only use that meter. This eliminates the need to constantly check what CAT environment you’re working in. If you’re surrounded by industrial motors and drives, you don’t want to thoughtlessly reach for the wrong meter. Go ahead, find a nice shelf in the workshop and start a multimeter museum for the retired ones.
Don’t Confuse the Fuses: Make sure that the DMM you purchase has ceramic, HRC (high rupturing capacity) fuses for all high voltage functions. These fuses can respond quickly giving you a time advantage for a safe reaction and they can absorb extant voltage before it gets to you. If a fuse ever blows, you might want to give it some respect—it may have just saved your life. Here’s an idea for another shelf for the workshop museum—a war story behind every blown fuse. More importantly, be sure you replace all fuses with one that matches the ratings specified by your meter maker.
Too Hot to Handle: Many newer multimeters include temperature measuring capabilities using thermocouple or thermistor probes. These Type K probes require contact and can deliver an accurate temperature reading on a number of surfaces. Sometimes, that very contact however, can be hazardous. To avoid burns or dangerous proximity to moving equipment, use a non‐contact infrared thermometer or “pyrometer” to get a safe point‐and‐shoot temperature reading from a distance.
Look for "distance to spot" ratios that permit precise one‐inch spot readings from a safe distance. For example, a 12:1 IR thermometer provides a reading of a one‐inch area from 12 inches away. A 30:1 IR thermometer provides a safer reading of an identical one‐inch spot from 30 inches away. Further is better when it comes to safety.
While you can purchase an IR thermometer separately, newer digital multimeters are available with an IR thermometer built right in, saving you money and helping you keep your tool box clutter‐free. Many already offer a bead probe thermometer built in. You should expect the infrared thermometer as well for convenience and safety.
Leads by Example: Your CAT IV multimeter should come with CAT IV test leads. This should be a no‐brainer. What’s the point in having all that protection built into your DMM if the leads will be turning to putty in your hands? Look for professional‐grade, CAT IV‐rated test leads. This is not a place to save a few bucks. You wouldn’t put soft, cushy touring tires on a sports car and expect it to take the exit without a lot of drama. Same thing here: always ask for manufacturer‐specified test leads with matching CAT ratings.
2. Accuracy
Multimeters may have similar looking dials that indicate they seem to perform the same functions. Besides safety factors discussed above, what makes them different? A key distinguishing feature is accuracy. What kind of precision will your digital multimeter provide? Don’t assume that because a multimeter is digital instead of analog that it is automatically a high‐accuracy instrument.
When Smaller is Better: There are two things too look for when it comes to accuracy. The first is the basic accuracy percentage listed by the manufacturer on a spec chart. This is a very important spec to look for. If you can’t find it listed on the product packaging or description, stay away. Accuracy is obviously not a concern for this manufacturer. When you compare accuracy specs, the smaller the value, the more accurate the meter.
In other words, a digital multimeter with a 6% accuracy rating means readings can vary plus or minus 6%. A 0.6% accuracy reading is better because now, variances will only be two‐tenths of a percent. Take it a level deeper and look for a 0.06% accuracy reading. Now we’re talking precision: variances will range only by six one‐hundredths of a percent.
[Optional related chart]
Evaluating Accuracy
6%-Good 0.6%-Better 0.06%-Best
Tell me True: The second accuracy‐related factor you should make sure you check is whether it’s a True RMS multimeter or an averaging meter. True RMS meters ensure readings from non linear loads are accurate. As power semiconductors and rectifiers make their way into newer adjustable speed motor drives and controls, a meter must compensate for current being drawn in short pulses instead of a clean sine wave. A meter that is not true‐RMS can be off by as much as 40% when measuring such line side currents.
If you’re looking for the "maximum multimeter," make sure it’s True RMS.
3. Versatility
This article started out by referring to a digital multimeter as a key tool in your toolbox arsenal. DMMs are such an important tool because of their versatility. No longer do we have voltmeters and ammeters. Now we have multi‐meters. They are effectively the Swiss Army knife of test equipment. But, as with Swiss Army knives, some have more tools than others, and some have more useful tools than others. The same applies for digital multimeters.
Dialed Up: Besides the obvious need to measure voltage (VDC and VAC) and current (A), you should look for a DMM that offers advanced capabilities. A comprehensive set of functions may include resistance (Ohms), duty cycle (%), capacitance (nF), and frequency (Hz). Open circuit voltage (2.8V) for diode and continuity testing is indispensable. As mentioned above, temperature readings via Type K (thermistors) probes and a built‐in infrared thermometer or pyrometer help take some DMMs into another category of multi‐functionality altogether.
Push Button Convenience: More buttons on a digital multimeter equals more bells and whistles. DMMs come with a number of convenient must‐have functions that expand their ability to measure by also capturing or calculating key values during testing.
For example, one‐button access to minimum and maximum values can help identify problems. An averaging function can help deliver a big‐picture perspective. Hold, relative value, and peak hold functions are very useful diagnostic tools to capture instances that fall out of the normal range.
Display Your Findings: The LCD display itself can make your meter more useful. A dual display couples the precision of a digital numerical readout with a bargraph that simulates the sweep of an analog multimeter needle. Sometimes, testing just requires seeing that swing of the needle and a digital bar graph can approximate that. Finally, you want to make sure your display is backlit. Don’t assume it is. You can’t always rely on external light and being able to accurately see your readout is essential.
4. Reliability
Everyone has an uncle or older co‐worker who loves to regale you with stories about his warhorse multimeter that’s seen it all. Despite the limited functionality that it may have, one thing is for certain: it’s proven to be reliable. How can you ensure that your investment will endure similarly?
Built Tough: Look for a design that is made to withstand rough handling and the occasional drop. One example is a double‐molded design that literally adds an extra shell of protection to the multimeter. Also, is it splash‐resistant? You don’t want a ruined multimeter because you were outside during a passing shower.
Warranty Worries? No matter what you do to keep your meter in top shape as long as possible, there will be times when a failure warrants a replacement. You want to know that the multimeter maker stands behind its products with a warranty that ensure peace of mind. Avoid anything with curiously brief warranty periods (e.g., 90 days, 6 months, etc.) that look like they could have been copy and pasted from a toaster at Wal‐Mart.
While a lifetime warranty cannot be beat, make sure you read the fine print to verify that the lifetime portion of the warranty is actually useful and not a hard‐to‐enforce technicality. A useful industry standard is a three year warranty. Plus, check that the company has a U.S.‐based customer and technical support team you can count on and contact directly by phone. Sometimes that direct access to a person can make a world of difference compared to a corporate phone menu.
5. Value
Two of the most popular purchasing misconceptions we invariably and reluctantly discover the hard way are that 1) not everything expensive is worth it; and 2) a good value is different than a cheap price. Let’s take a closer look with regard to digital multimeters.
Nowadays, when you make an apples‐to‐apples comparison of multimeter specs, you discover that prices for comparable models from different companies can vary wildly. You have to wonder if models from some “legacy brands” are priced high because they’re resting on the laurels of their reputation founded back in the muscle car era?
Clearly, it’s important to work with well‐known, reputable brands, but in the current economy, electrical professionals are taking a closer look at different DMM makers. They need to make the best use of their hard‐earned dollars and get the most bang for their buck. What they’re discovering is that value has more to do with the best combination of features backed by a company that is accessible and that will support them.
A Closer Look: the Extech EX570
One company that has tried to offer the best combination of features in an affordable digital multimeter designed for industrial use is Extech. Based in Waltham, Massachusetts since 1971, Extech unveiled the latest addition to its EX500 series of industrial‐duty multimeters earlier this year.
The new EX570 is ideal for industrial, plant maintenance and MRO electrical technicians. In addition to comprehensive multimeter functions, high accuracy (0.06%), and True RMS precision, the EX570 protects users with Category IV‐600V (and Category III‐1000V) safety ratings. Additionally, the EX570 features an integrated infrared thermometer, a patented function only found on Extech meters.
The new Extech EX570 is designed to withstand harsh environments and usage with a rugged, double‐molded housing. The large, illuminated LCD displays a 5‐digit readout (to 40,000 counts) and a useful 40‐segment bar graph for analog comparisons and quick “needle‐swing” tests.
The EX570 offers a wide array of must‐have multimeter measurements (including capacitance, frequency, diode and continuity functions) coupled with convenient, one‐button access to frequently used functions: Min./Max., Average, Hold, Relative, and Peak Hold. Store up to three measurements in the onboard memory.
In addition to type K thermocouple temperature measurements, the EX570 offers an integrated infrared thermometer for safe, point‐and‐shoot, non‐contact temperature measurement with a useful 30:1 spot‐to‐distance ratio. The EX570 not only ensures electrical technicians can perform all essential electrical diagnostics, the built‐in IR makes it easy to identify overheating motors, electrical panels, and other components from a distance and without an additional meter.
Extech backs the EX570 with a three‐year warranty and it comes with double‐molded test leads, type K bead wire temperature probe (thermistors), magnetic hanging strap, 9V battery and storage case.
Conclusion
In this economy, we all want to do more with less. We’re voting with our wallets in many cases, but we want to make sure it’s still a sound decision. This article looks at how to find a “maximum multimeter,” one that helps you do more, with more, for less. Remember to look for safety, accuracy, versatility, reliability and value. With those factors in mind, you can find your “maximum multimeter.”
Related Table: Categories by the Numbers
IEC Overvoltage Category Operating Voltage Peak Transient
CAT I 600 V 2500 V
CAT I 1000 V 4000 V
CAT II 600 V 4000 V
CAT II 1000 V 6000 V
CAT III 600 V 6000 V
CAT III 1000 V 8000 V
CAT IV 600 V 8000 V
