The weakest link: Does your digital
multimeter meet today’s standards?

Compliance with UL 3111-1 reduces digital multimeter shock and arcing hazards from transient voltage spikes.

Electricians working on panel and distribution systems rely on their tools (and training) to keep them from becoming a direct connection between hot wires and ground. 

Personal protective equipment, such as flame-resistant clothing, safety glasses or a face shield and properly rated gloves help protect the worker from serious arc and electrocution hazards.

But ironically, the most sophisticated tool in an electrician’s pouch – the digital multimeter – may be the one tool that subjects a worker to the greatest risk, says John Green, director of marketing at Greenlee.

“It’s mind-boggling that electricians are very careful to make sure their hand tools and personal protective equipment meet safety standards. But when it comes to digital multimeters, they often use the least expensive units they can find,” he says.

Outside of incorrectly using the meter, the greatest risk comes from transient voltage spikes that can push 10 times the normal voltage or more through power lines in an instant, without warning. “Transient voltage events are becoming more frequent as motors, capacitors and variable-speed drives are installed. Lightning can also cause transient voltage spikes,” he says.

If you are testing a circuit and a high transient voltage event occurs, the voltage can overpower the safety factor designed into the digital multimeter. These transient power surges also expose the worker to shock or arc-burn risks which can cause serious injury or death.

Categories help define risk, tools
International standards drive the category ratings of electrician’s tools. For example, digital multimeters are now covered by the International Electrotechnical Commission’s (IEC) 61010-1 published in 1990. It identified Category I, II, and III ratings. Category IV ratings were added in the 2nd edition of the standard, published in 2001. Underwriter Laboratories (UL) published UL 3111-1 in 1994 to mirror the standards set out by the IEC in 61010-1. UL 3111-1 replaces the decades-old UL 1244 standard that was based on the IEC 348 standard. It considers the need for transient overvoltage protection. UL 3111-1 is presently being revised to add Category IV ratings.

“Many meters on the market today do not meet the UL 3111 standard. Greenlee has tested and redesigned its digital multimeter line to meet this standard and has even tested and produced meters that can withstand Category IV ratings,” says Green.

There is no requirement by the IEC that digital multimeters be verified to meet any category rating. But Green says, from a safety standpoint, it’s very important that meters go through a third-party verification process, such as the Underwriters Laboratories or other testing organization. “For example, Greenlee digital multimeters that meet the standard are tattooed with the UL seal and the tool’s category rating. The UL, cUL or GS/TUV ratings are other possible markings,” Green adds.

Category ratings defined
As the category rating increases, the chances for and the severity of a transient voltage event increases. The tools are rated on their ability to withstand a voltage spike which is applied through a certain maximum low level of resistance. (See table.)

Category I-rated tools are signal-level tools for telecommunications and electronic equipment. Transient voltage risk is limited, but exists, because of the distance and other equipment located between it and the primary electrical supply.

Category II-rated tools cover the local level of circuits for fixed or non-fixed powered devices. This includes most lighting, appliances, and 120- or 240-volt equipment inside a building.

Category III-rated tools can withstand the transient voltage range that can be found on distribution circuits. These tools are used on fixed primary feeders or branch circuits. They are separated from Category IV utility service or other high-voltage sources by at least one level or transformer isolation.

Category IV-rated tools are designed to be used for testing on the primary supply source but also includes 120- or 240-volt lines that power detached buildings or underground lines that power well pumps.

Redesigned tools
Green says Greenlee and other leading companies tested their digital multimeters and found that most of them did not meet the level of protection outlined in the IEC 61010-1 and UL 3111-1 standards. They immediately went to the drawing board. “The meters had to be redesigned with heavier, more expensive buses and fuses with a higher breaking capacity. We also made the distance between the fuse connectors wider to prevent arcing in an over-voltage situation,” he says.

Because of the greater margin of safety of the tools that meet the new UL 3111-1 standard, Green suggests looking at replacing your digital multimeter. “A meter that meets the Category III rating costs about $50; a Category IV-rated meter will cost around $200. “You’ll also find the new multimeters combine various tools to free up space in your toolbag. Some of them offer non-contact testing for certain jobs. Others feature a voltage/continuity tester with a ground-fault circuit function and built-in flashlight. The cost of a new meter that does more and meets today’s standard is a very small price when compared with the shock or arc hazard and the chance to upgrade to a tool that may make work simpler,” he says.

Published in the July/August, 2002 issue of Contractor Tools and Supplies magazine.

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