How to Go Home Safely at the End of Your Day

From Fluke Corp.

Safety standards are written to make sure we all go home safely at the end of the day. For electrical safety, the hazards can be deadly and manifest themselves quickly, often leaving no response time.

Engineers, electricians and technicians must follow safe work practices when using multimeters, including inspection before use. To help verify safety, the Occupational Safety and Health Administration (OSHA) requires employees to demonstrate their ability to select, inspect, use and maintain their test equipment.

Qualified Persons

OSHA regulations and the NFPA 70E Standard for Electrical Safety in the Workplace^® provide procedural guidance when it comes to test equipment inspection. For example, NFPA 70E^® states that only "qualified persons" are allowed to perform tasks that include the use of test equipment on systems 50V and greater. A digital multimeter is the most commonly used instrument for these kinds of measurements.

Since 2007, OSHA regulations require technicians to demonstrate their skills to their employer to be considered a qualified person. Thus, employers must verify an individual's ability to safely use digital multimeters.

Properly Rated for the Circuit

A digital multimeter, or any electrical measurement tool, must be properly rated for the circuit on which it is to be applied. Technicians must be able to understand and explain these ratings. Accessories like test probes, flexible clamps or others are included in these ratings. And the ratings should always be printed on the tools.

The first step is to identify the nominal system voltage of the circuit to be tested. This is the voltage class assigned to systems and equipment and can be found on nameplates and drawings. Typical nominal voltages found in plants are 120/240, 208Y/120 and 480Y/277.

Technicians must be aware of the extreme danger of using an inadequately rated digital multimeter. Using a 1,000V-rated digital multimeter on medium-voltage circuits has, unfortunately, happened more than once with tragic results.

Nationally Recognized Testing Laboratory

In addition to proper voltage and current ratings, test tools must be listed by a Nationally Recognized Testing Laboratory (NRTL) and properly labeled with the NRTL's mark. These marks should be displayed on your tools and accessories.

OSHA lists which NRTLs have been approved to test and verifies that tools meet their standards. This testing reasonably assures products are safe for use in the environments for which their ratings are designed. Once the equipment meets the testing laboratory's criteria, the tool can be labeled with the NRTL's recognized mark. Test equipment without a label should not be used.

Among the most common testing laboratory marks found on test tools are Underwriters Laboratories Inc. (UL), Canadian Standards Association (CSA), and TÜV. Technicians must demonstrate their ability to recognize and identify these labels and explain their importance.

CAT Ratings

Electrical workers must also be familiar with the Category Rating found on digital multimeters and other test tools and accessories. The "CAT" rating indicates the tool's ability to withstand transient overvoltage conditions that could destroy the meter and cause injury.

Tools used in distribution systems should be at least CAT III rated. CAT IV offers a greater degree of protection (see Figure 1). Most industrial digital multimeters are rated CAT III for use on systems 1,000V and below and CAT IV for 600V and below. Electrical workers should be able to identify the CAT rating needed for their job.

The ratings also should be easy to find on the tool, near the NRTL’s mark. These ratings are the voltage levels the laboratory has certified the tool to be able to withstand.

Designed for Environment and Use

Technicians must verify test instruments and their accessories are designed for both the environment and their use. For example, when examining a digital multimeter for proper design, ask, "Will this digital multimeter be used in a hazardous location?" When taking voltage readings, it’s possible for a very small electrical arc to be drawn when placing a test probe on, or removing a test probe from, an energized point.

The National Electrical Code^® (NEC) identifies environments as Hazardous (Classified) locations if explosive atmospheres are present. Intrinsically safe test tools are designed for use in these locations and technicians must look for the identification, if applicable. Look for a red tool or an EX symbol on the tool.

This is also a good reason to place and remove test probes at a 90º angle to the terminal, and not let the probe "slide" from one terminal to another.

Visual Inspection

A visual inspection should be done on the test tool and all associated test leads, cables, power cords, probes and connectors. Look for any obvious external defects. It’s not uncommon to find damaged test leads or probes, which must be replaced before use.

One method of visual inspection is to slowly pull test leads between your fingers. Your fingers can often feel if the insulation has been damaged, even if you can’t see it. All test leads should have a shroud around the end that is inserted into the digital multimeter. This prevents accidental shock should the test lead become unplugged from the tool while the probe is still on an energized component.

Test probes (both voltage and current probes) also have a voltage, amperage and category rating. Look for the IEC (International Electrotechnical Commission) symbol for "double-insulated" (one square box inside of another). This symbol tells you that one single insulation failure will not result in personnel being exposed to dangerous shock levels.

Don’t discount the use of clamps, flex clamps and test probes for current measurements for visual inspections. Such devices should be marked with a maximum current rating. They should also have the NRTL label. Many test probes are double insulated and marked with the double-insulated symbol.

Once you’ve done the visual inspection, never hesitate to remove a tool from service if there’s any question about its condition. Make sure some method, such as tagging, is used to prevent someone else from inadvertently using the defective test equipment before repairs are completed.

Three-Point or Live-Dead-Live Testing

One of the most critical safety tasks performed by a technician is verifying the absence of voltage during the lockout/tagout (LOTO) process at voltages of 50V or more (see Figure 2). A test tool that fails to operate properly during this test could result in a catastrophic accident.

This is why it’s vital that technicians properly perform the "three-point" or a “live-dead-live” test when verifying the absence of voltage during their qualification activities.

The process to verify voltage is as follows: