Safety Tip #5: Whenever possible, work on de-energized circuits and follow proper lockout, tag-out procedures.

Safety considerations for live measurements

Keep your eyes on the job at hand.

Measuring live voltages and current in today’s high energy environments can result in a severe hazard to equipment and users if proper precautions are not applied. Given the risk of transients, surges, and old fashioned human error, it always pays to follow safe work practices and use test instruments rated for the voltage or current you’re measuring. Whenever possible, work on de-energized circuits and follow proper lockout, tag-out procedures. If you have to work on live circuits, following the steps below will improve your measurement practices and help reduce any hazard.

Setup

1. Assess the environment before taking the measurement.

2. Do not work alone in hazardous areas.

3. Wear the appropriate Personal Protective Equipment (PPE) as determined by NFPA 70 E and

the local recommendations of health and safety personnel.

4. Make sure your test instrument is rated for the measurement environment.

5. Be familiar with and know how to use your equipment prior to any hazardous measurements.

Practices

1. Measure at the lowest energy point.

2. Keep your eyes on the area you’re probing and keep both hands free as conditions require.

3. For single phase, connect neutral first — hot second.

4. Use the three point test method

5. Use test probes with a minimum amount of exposed metal such as .12 in (4 mm) metal tip probes.

6. Keep one hand in your pocket unless you must use both hands for a good measurement.

Setup Environmental analysis

Before you open an equipment cabinet, look over your work environment. How do you plan to use your meter? Where will you mount it? Do you have clear access to the equipment in question? Have you been trained on or are you knowledgeable in the use of your meter? Are environmental hazards present, such as tree branches or water? Do you have enough light and ventilation?

Avoid working in dark areas. If you choose to work in a dark area, turn on the test tool’s backlight to brighten the display for easier viewing. And, if you’re working in a deep or recessed panel, use a test probe extender and probe light to illuminate the area to be probed. Be sure you can clearly view the point of measurement. The probe extender facilitates measurement by keeping your hands further away from the inside of the panel, reducing potential danger.

Also make sure you have a helper knowledgeable in electrical safety or let someone else know where you’re working. It’s never good practice to work alone on high energy circuits.

Practices

1. It is a good practice to measure voltage at the point of the lowest available energy. For example, if you are measuring voltage on a breaker panel, identify the lowest-rated breaker available, and make your measurement there. This way, you have more protection between yourself and the potential hazard

2. Effective steps should be taken to obtain the best reading within the necessary envelope of safety. If conditions require that both of your hands remain free for a safe measurement, set the instrument down; use the instrument’s bail stand (if it has one). Better yet, use a magnetic hanger to hang the unit at eye level on the edge of the panel. Don’t try to watch the meter while you make your measurement — always keep your eyes on your test probes.

3. When taking single-phase measurements, always connect the neutral lead first, the hot lead second. After taking your reading, disconnect the hot lead first, the grounded lead second.

4. When testing for voltage, use the three point test method.

1. Test a similar known live circuit first

2. Test the “circuit to be tested”

3. Re-test the first known live circuit.

This process verifies your test instrument is working properly — an important part of your personal safety.

5. When making measurements in or around high energy three phase distribution panels, use test probes with a minimum amount of exposed metal at the probe tips, such as .12 in (4 mm) metal tip probes. This reduces the risk of an accidental arc flash from probe tips being inadvertently shorted together between phases.

6. Keep one hand in your pocket or out of the panel and the measurement circuit. You don’t want to offer a closed circuit. Whenever possible, use a properly rated alligator clip to attach the black test lead to the circuit under test. This gives you a free hand to probe with the red test lead.

Safety Tip #4: Look for the safety listing agency’s emblem on the meter

What are the Standards?

To provide improved protection for users, industry standards organizations have taken steps to clarify the hazards present in electrical supply environments. The American National Standards Institute (ANSI), the Canadian Standards Association (CSA), and the International Electro-Technical Commission (IEC), have created more stringent standards for voltage test equipment used in environments of up to 1000 volts.

ANSI, CSA and IEC define four measurement categories of over-voltage transient impulses. The rule of thumb is that the closer the technician is working to the power source, the greater the danger and the higher the measurement category number. Lower category installations usually have greater impedance, which dampens transients and helps limit the fault current that can feed an arc.

• CAT (Category) IV is associated with the origin of installation. This refers to power lines at the utility connection, but also includes any overhead and underground outside cable runs, since both may be affected by lightning.

• CAT III covers distribution level wiring. This includes 480-volt and 600-volt circuits such as 3-phase bus and feeder circuits, motor control centers, load centers and distribution panels. Permanently installed loads are also classed as CAT III. CAT III includes large loads that can generate their own transients. At this level, the trend to using higher voltage levels in modern buildings has changed the picture and increased the potential hazards.

• CAT II covers the receptacle circuit level and plug-in loads.

• CAT I refers to protected electronic circuits.

Independent testing labs help ensure safety compliance You want your tools and equipment to help you work safely. But how do you know that a tool designed to meet a safety standard will actually deliver the performance you are paying for? Unfortunately it’s not enough to just look on the box. The IEC (International Electrotechnical Commission) develops and proposes standards, but it is not responsible for enforcing the standards. Wording like “Designed to meet specification...” may not mean a test tool actually performs up to spec. Designer’s plans are never a substitute for an actual independent test.

That’s why independent testing is so important. To be confident, check the product for the symbol and listing number of Underwriters Laboratories (UL), the Canadian Standards Association (CSA), TÜV or another recognized testing organization. Those symbols can only be used if the product successfully completed testing to the agency’s standard, which is based on national/ international standards. That is the closest you can come to ensuring that the test tool you choose was actually tested for safety.

What does the CE symbol indicate?

A product is marked CE (Conformité Européenne) to show it conforms to health, safety, environment and consumer protection requirements established by the European Commission. Products from outside the European Union cannot be sold there unless they comply with applicable directives. But manufacturers are permitted to self-certify that they have met the standards, issue their own Declaration of Conformity, and mark the product “CE.” The CE mark is not, therefore, a guarantee of independent testing.

Don’t be confused by “Listed” vs. “Designed to” in your test tools. IEC sets the standards but does not test or inspect for compliance. So a manufacturer can claim to “design to” a standard with no independent verification. To be UL-Listed, CSA or TUV-Certified, a manufacturer must employ the listing agency to TEST the product’s compliance with the standard. Look for the listing agency’s emblem on the meter.

Safety Tip #3: Before starting any job, confirm that the DMM and test leads are rated for the category and voltage level appropriate for the work

Category ratings, safety standards

Electrical measurement category ratings are defined by the safety standard, IEC 61010, and are separated into four distinct category ratings, CAT I, CAT II, CAT III or CAT IV Other requirements of IEC61010 to be familiar with include those relating to transient test, dielectric withstand voltage, clearance spacing, exposed metal probe tips, impact and markings.

The NFPA 70E standard also requires that the test tools used on the job be rated for the environment they will be used in. This applies to both the meter and the test leads/probes, and any PPE (Personal Protective Equipment) necessary for safe measurements. PPE ratings are somewhat different than CAT ratings.

IEC 61010 Electrical measurement category ratings for test tools

Important note: CAT ratings on test tools are different than hazard/risk category ratings on PPE gear. CAT ratings are determined by the potential transient impulse in the workplace that a connected test tool might experience. PPE requirements are determined by the surface energy level a user might experience.