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.

Safety Tip #2: Don’t risk CAT IV areas without the right leads

What’s the difference in test leads?

Not all test leads are created equal. It’s very common to accumulate test leads over the years and mix them up with the newer, more robust leads available today. Test leads, just like the testers themselves, have been upgraded to meet the new safety standards established for today’s electrical environments. These standards require that the insulation between the test lead conductor and your fingers have the minimum distance to stand off the hazards that exist in the environment in which you are working. There should also be a finger guard on the outside of the probe that establishes the proper distance between your fingers and the exposed metal parts of the probe. These distances and insulating ratings have been predetermined for each installation category and voltage rating.

What’s the difference in test leads?

Not all test leads are created equal. It’s very common to accumulate test leads over the years and mix them up with the newer, more robust leads available today. Test leads, just like the testers themselves, have been upgraded to meet the new safety standards established for today’s electrical environments. These standards require that the insulation between the test lead conductor and your fingers have the minimum distance to stand off the hazards that exist in the environment in which you are working. There should also be a finger guard on the outside of the probe that establishes the proper distance between your fingers and the exposed metal parts of the probe. These distances and insulating ratings have been predetermined for each installation category and voltage rating.

Another characteristic to watch for is the amount of current test leads can safely handle. In the previous example, the Fluke 170 and 180 Series products are fused to a maximum current of 10 A. When measuring current using test leads with a current rating less than 10 A could cause the test leads to become overheated. This in turn could cause the insulation to melt and compromise the safety rating of the leads. Again, discard all leads that have discoloration or appear to have melted insulation and replace them with new ones.

Category IV ratings

Recently the International Electrotechnical Commission (IEC), an organization that develops safety standards, defined the standards for Category IV environments. This environment includes overhead power lines, underground power lines, and service entrance power. These are environments where electricians make measurements every day. In order for you to make measurements in these environments safely, Fluke has upgraded most of its test lead products to meet the new CAT IV standards. If you find yourself making measurements in these areas and have an older set of leads, you might want to consider replacing them with leads that are clearly marked as rated for CAT IV.

Safety Tip #1: Choosing the correct fuse for your tester can avoid hidden dangers like serious burns & possibly even death

Why does a tester need fuses?

There are a variety of testers on the market, from simple voltage detectors to highly sophisticated digital multimeters (DMMs). Testers that make voltage measurements have a high input impedance that makes an overcurrent condition unlikely. As a result, voltage measuring inputs are generally not designed with fuse protection but with overvoltage protection. But if that same tester is designed to also measure current, fusing is required. Current measuring inputs usually employ a simple shunt through which the measured current flows. This shunt’s resistance is on the order of 0.01 ohms. Add to that the resistance of the test leads (approx. 0.04 ohms), and you have a short of less than 0.1 ohms. This resistance is adequate when you place this short in series with another load to measure the circuit’s current. But it’s an altogether different story when you place this circuit across a voltage source, say the plug outlet in your living room.

This is an all too common mistake made by people measuring both voltage and current. After making a current measurement with the test leads in the current input jacks, the user tries to make a voltage measurement forgetting the leads are in the amps jacks. This effectively places a short across the voltage source. Years ago, when analog meters were the only instrument for making these measurements, this mistake pretty well destroyed the meter movement (the needle wrapped around the top peg), not to mention the internal circuitry. To protect against this common occurrence, meter manufacturers started putting a fuse in series with the meter’s test lead jacks, for an inexpensive and effective solution for a very simple mistake.

Today, most manufacturers still design their testers with fuse protection in the current measuring circuits. As technology has moved forward, the science of fuse design has progressed as well. Although understood by people who build testers, the full impact of fusing is little understood by most tester users. When you make that simple mistake of putting voltage across the current jacks and blow the fuse, you’re at first thankful you didn’t wipe out the meter. But you may then become annoyed with the fact that you have to hunt up a new fuse and replace it before making your next current measurement. Even more frustrating is when you share meters with other people in your shop and someone else blows a fuse and puts the meter away to have the problem discovered by an unsuspecting user.

Using the proper fuse

Specially designed “high-energy” fuses are designed to keep the energy generated by such an electrical short within the fuse enclosure, thus protecting the user from electric shock and burns. These high-energy fuses are designed to limit the length of time the energy is applied and the amount of oxygen available for combustion. Fuses can not only be designed to open at a specified constant current, but at an instantaneous high current as well. This high current is specified as “minimum interrupt current.” Fluke uses fuses with a minimum interrupt rating of 10,000 and 17,000 amps in their testers.

If you take a CAT III 1000 V meter with the test leads in the amps jacks, you will have a series resistance of approximately 0.1 ohms (0.01 for the shunt, 0.04 for the test leads and 0.05 for the fuse and circuit board conductors) between the leads. Now when you accidentally place the leads across a 1,000 volt source, by Ohms Law you will generate a current of 10,000 amps (E/R=I, 1,000/0.1 = 10,000). You want a fuse that will break that current and do it quickly.

In addition to the specially designed fuse element, the high energy fuse is filled with sand. The sand will not only help absorb the shock energy created by the exploding element, but the high temperatures (up to 10,000 °F) generated by the energy will melt the sand and turn it to glass. The glass coats the element and smoothers the fireball by cutting off the available oxygen, keeping you and the tester safe from harm. As you can see, not all fuses of the same amperage and voltage rating are the same. For your own safety you need to be sure the fuses you use are the ones the engineer designed into the tester.

Always refer to the tester’s manual, or check with the tester manufacturer to ensure you have the correct fuse. You can always get replacement fuses for Fluke testers by ordering the part number listed in the tester’s manual. Your safety is worth much more than the money it takes to purchase the proper fuse for which the tester was designed.

ADMET 2011

Fluke introduces ScopeMeter® 190 Series II Portable Oscilloscopes engineered for harsh industrial environments

Four-channel scopes go anywhere there is trouble

Fluke Corporation, the global leader in portable electronic test and measurement technology, has introduced the Fluke ScopeMeter® 190 Series II handheld portable oscilloscopes, the first four-channel scopes designed for harsh industrial environments.

These new portable scopes are the first safety rated for CAT III 1000 V / CAT IV 600 V environments. The four input channels are fully isolated from each other to perform differential floating measurements, a critical consideration for troubleshooting fixed-installation three-phase power electronic devices like variable speed motor drives.

The Fluke ScopeMeter chassis is sealed from the environment with no cooling slots or fans to expose the instrument. It carries the International Protection (IP) -51 dust and drip proof rating so it’s tough enough to use safely on the factory floor and in the field. While most high-performance oscilloscopes are not designed to withstand dirty and harsh environments, the Fluke ScopeMeter is built tough to deliver accurate results where ordinary portable oscilloscopes dare not go.

The Fluke 190 Series II oscilloscope meets the growing need for four-channel portable oscilloscopes in industrial environments. Power electronics are used increasingly in solar and wind energy generation and to maximize efficiency or reduce power consumption especially in heavy-duty electro-mechanical applications. With the new Fluke 190 Series II ScopeMeter, users can see more and fix more using all four channels.

Their fast sampling rate, up to 2.5 GS/sec and 400 pico second resolution, helps users capture electrical noise and other disturbances to diagnose exactly what is going on. With100 MHz and 200 MHz models, they deliver the bandwidth needed to cover both today’s needs, and tomorrow’s. With four channels, users can inspect input signals, output signals, feedback loops, or safety interlocks simultaneously to solve problems like:

• Signal amplitude or shape variations, induced noise or disturbances across critical

circuit nodes.

• Signal timing measurements and synchronization issues.

• Attenuation, fluctuation, drift as a result of impedance issues or environmental impacts.

Four channels are indispensable in testing variable speed motor drives and inverter power electronic technology used in green energy generation and transportation applications. Users can:

• View and measure harmonics, transients, and loads in three-phase power systems.

• Troubleshoot dc to ac converters for faulty insulated-gate bipolar transistors (IGBTs)

and control circuits.

• View and measure pulse width modulated waveforms (PWM) for reflections and

transients.

These new test tools are convenient and user-friendly. New, high-performance Li-ion battery technology keeps the Series II ScopeMeter on the job for up to seven hours. An external charger and easy-access battery door makes it simple to swap batteries and extend usage. Two USB ports, electrically isolated from measurement input circuits, make it easy to capture and share waveforms. Users can conveniently store data to a USB memory device or easily connect to a PC via the USB port and transfer waveforms or screen images for data analysis or archive.