ABCs Of Multimeter Safety: Multimeter Safety And You
APPLICATION NOTEABCs of multimeter safety:Multimeter safety and youDon’t overlook safety—your lifemay depend on it.Where safety is a concern, choosinga multimeter is like choosing amotorcycle helmet—if you value yourhead, get a safe helmet. The hazardsof motorcycle riding are obvious, butwhat about multimeters? As longas you choose a multimeter with ahigh enough voltage rating, aren’tyou safe? Voltage is voltage, isn’t it?Not exactly. Engineers who analyzemultimeter safety often discover thatfailed units were subjected to a muchhigher voltage than the user thoughthe was measuring. Occasionally,accidents occur when a meter ratedfor low voltage (1000 V or less), isused to measure medium voltage,such as 4160 V. In other instances, itwas a momentary high-voltage spikeor transient hits the multimeter inputwithout warning.Voltage spikes—an unavoidablehazardAs distribution systems and loads become morecomplex, the possibilities of transient overvoltages increase. Motors, capacitors and powerconversion equipment, such as variable speeddrives, can be prime generators of spikes. Lightning strikes on outdoor transmission lines alsocause extremely hazardous high-energy transients. If you’re taking measurements on electricalsystems, these transients are “invisible” andlargely unavoidable hazards. They occur regularlyon low-voltage power circuits, and can reachpeak values in the many thousands of volts. Inthese cases, you’re dependent for protection onthe safety margin already built into your meter.The voltage rating alone will not tell you howwell that meter was designed to survive hightransient impulses.Early on, clues about the safety hazard posedby spikes came from the supply bus of electriccommuter railroads. The nominal bus voltagewas only 600 V, but multimeters rated at 1000 V189 TRUE RMS MULTIMETERTEMPERATUREmAAA10A MAXFUSEDlasted only a few minutes whenmeasurements were takenwhile the train was operating. A close look revealed thatthe train stopping and starting generated 10,000 V spikes.These transients had no mercyon early multimeter inputcircuits. The lessons learnedthrough this investigation ledto significant improvementsin multimeter input protectioncircuits.Test tool safety standardsTo protect you against transients, safety must be built intothe test equipment. What performance specification shouldyou look for, especially if youknow that you could be working on high-energy circuits?The task of defining safetystandards for test equipment isaddressed by the InternationalElectrotechnical Commission(IEC). This organization developsinternational safety standardsfor electrical test equipment.VCOM400mAFUSEDCAT1000VMeters have been used for yearsby technicians and electricians yet the fact is that metersdesigned to the IEC/EN 61010standard offer a significantlyhigher level of safety. Let’s seehow this is accomplished.
Understanding measurement categories: Different locationsCAT III208 V230V/120 VCAT IVO FFO NO FFO NO FFO NO FFO NO NO FFO FFO FFO NO NO NO FFO FFO FFO NO NO NO FFO FFO FFO NO NO NO FFO FFO FFUtility supplyO NO NO NO NO FFCATCATII II208230V/120V VO FFCAT IV400 VCAT III230 V VFD240 CAT IIIFixed mount loadFigure 1. Measurement categories in different locationsTransient protectionThe real issue for multimeter circuit protection isnot just the maximum steady state voltage range,but a combination of both the steady state andthe transient overvoltage withstand capability.Transient protection is vital. When transients rideon high-energy circuits, they tend to be moredangerous because these circuits can deliverlarge currents. If a transient causes an arc-over,the high current can sustain the arc, producinga plasma breakdown or explosion, which occurswhen the surrounding air becomes ionized andconductive. The result is an arc blast, a disastrousevent which causes more electrical injuries everyyear than the better known hazard of electricshock. (See “Transients–the hidden danger” onpage 4.)MeasurementcategoryIn brief Refers to the “origin of installation,” i.e., whereThree-phase atlow-voltage connection is made to utility powerutility connection,any outdoor mains Electricity meters, primary overcurrentprotection equipmentconductors Outside and service entrance, service drop frompole to building, run between meter and panel Overhead line to detached building,underground line to well pumpCAT IIIThree-phasedistribution,including singlephase commerciallighting Equipment in fixed installations, such asswitchgear and polyphase motors Bus and feeder in industrial plants Feeders and short branch circuits, distributionpanel devices Lighting systems in larger buildings Appliance outlets with short connections toservice entranceCAT IISingle-phasereceptacle connected loads Appliance, portable tools, and other householdand similar loads Outlet and long branch circuits– Outlets at more than 10 meters (30 feet) fromCAT III source– Outlets at more than 20 meters (60 feet) fromCAT IV sourceMeasurement categoriesThe most important single concept to understand about the IEC/EN 61010 standards is theMeasurement Category. The standard definesCategories II through IV, often abbreviated as CATII, CAT III, CAT IV, etc. (See Figure 1.) The divisionof a power distribution system into categories isbased on the fact that a dangerous high-energytransient such as a lightning strike will beattenuated or dampened as it travels through theimpedance (ac resistance) of the system. A higherCAT number refers to an electrical environmentwith higher power available and higher energytransients. Thus a multimeter designed to a CATIII standard is resistant to much higher energytransients than one designed to CAT II standards.2 Fluke CorporationExamplesCAT IVTable 1. Measurement categories. IEC/EN 61010 applies to low-voltage ( 1000 V) testequipment.ABCs of multimeter safety: Multimeter safety and you
Within a category, a higher voltage rating denotesa higher transient withstand rating, e.g., a CATIII-1000 V meter has superior protection compared to a CAT III-600 V rated meter. The realmisunderstanding occurs if someone selects aCAT II-1000 V rated meter thinking that it issuperior to a CAT III-600 V meter. (See “When is600 V more than 1000 V?” on page 7.)It’s not just the voltage levelA technician working on office equipment couldactually encounter non-mains voltages muchhigher than the power line ac voltages measuredby the motor electrician in the CAT III location.Yet transients in electronic circuitry, whatever thevoltage, are clearly a lesser threat, because theenergy available to create an arc is quite limited.This does not mean that there is no electricalhazard present in non-CAT rated environment.The primary hazard is electric shock, not transients and arc blast. Shocks, which will bediscussed later, can be every bit as lethal as arcblast.To cite another example, an overhead line runfrom a house to a detached workshed might beonly 120 V or 230 V, but it’s still technically CATIV. Why? Any outdoor conductor is subject tovery high energy lightning-related transients.Even conductors buried underground are CAT IV,because although they will not be directly struckby lightning, a lightning strike nearby can inducea transient because of the presence of highelectro-magnetic fields.When it comes to Overvoltage Installation Categories, the rules of real estate apply: it’s location,location, location. (For more discussion of InstallationCategories, see page 6, “Applying categories to your work.”)Independent testing is the key to safetycomplianceLook for a symbol and listing number of an independent testinglab such as CSA, RCM or other recognized testing organization.Beware of wording such as “Designed to meet specification .”Designer’s plans are never a substitute for an actual independent test.How can you tell if you’re getting a genuine CAT III or CAT IVmeter? Unfortunately it’s not always that easy. It is possible fora manufacturer to self-certify that its meter is CAT II or CAT IIIwithout any independent verification. The IEC develops andproposes standards, but it is not responsible for enforcing thestandards.Look for the symbol and listing number of an independenttesting lab such as CSA, RCM or other recognized approvalagency. That symbol can only be used if the product successfully completed testing to the agency’s standard, which is basedon national/international standards. UL 61010-1, for example,is based on IEC/EN 61010-1. In an imperfect world, that isthe closest you can come to ensuring that the multimeter youchoose was actually tested for safety.What does thesymbol indicate?A product is marked CE (Conformité Européenne) to indicate itsconformance to certain essential regulations concerning health,safety, environment and consumer protection established by theEuropean Commission and mandated through the use of “directives.” There are directives affecting many product types, andproducts from outside the European Union can not be importedand sold there if they do not comply with applicable Europeandirectives. Compliance with the directive can be achieved byproving conformance to a relevant technical standard, such asIEC/EN 61010-1 for low-voltage products. Manufacturers arepermitted to self-certify that they have met the standards, issuetheir own Declaration of Conformity, and mark the product“CE.” The CE mark is not, therefore, a guarantee of independenttesting.Tool tipTwo pole voltage testers are a safe and quick way to check for the presence oflive voltage on ac or dc circuits, switches and outlets before working on this circuits. Please follow the instructions below:1. Check that the voltage tester is not damaged by visual inspection.2. Make sure the voltage tester is rated for the level of voltage being tested.3. Test the function of the voltage tester on a known voltage source or on aproving unit.4. Disconnect the circuit from mains supply.5. Ensure that the circuit cannot be re-energized.6. Test for the absence of voltage.According to the local safety regulations a contact type (two pole) voltage testeror a digital multimeter may be used only test for the absence of voltage.3 Fluke CorporationABCs of multimeter safety: Multimeter safety and youA two-pole voltagetester or a digitalmultimeter may beused only to testfor the absence ofvoltage.
Protection against two majorelectrical hazardsstart to burn away, drawingan arc from the contact pointto the probe.Transients–the hidden dangerLet’s take a look at a worst-case scenario inwhich a technician is performing measurementson a live three-phase motor control circuit, usinga meter without the necessary safety precautions.Here’s what could happen:1. A lightning strike causes a transient on thepower line, which in turn strikes an arcbetween the input terminals inside the meter.The circuits and components to prevent thisevent fail. Perhaps it is not a CAT III or CATIV rated meter. The result is a direct shortbetween the two measurement terminalsthrough the meter and the test leads.2. A high-fault current–possibly several thousands of amps–flows in the short circuit justcreated. This happens in thousandths of asecond. When the arc forms inside the meter,a very high-pressure shock wave can cause aloud bang—very much like a gunshot or a carbackfiring. At the same instant, the tech seesbright blue arc flashes at the test lead tips–thefault currents superheat the probe tips, which13. The natural reaction is topull back, in order to breakcontact with the hot circuit.But as the tech’s hands arepulled back, an arc is drawnfrom the motor terminal toeach probe. If these two arcsjoin to form a single arc,there is now another directphase-to-phase short, thistime directly between themotor terminals.4. This arc can have a temperature approaching 6000 C,which is higher than thetemperature of an oxyacetylene cutting torch! As thearc grows, fed by available short circuit current, itsuperheats the surroundingair. Both a shock blast and aplasma fireball are created.If the technician is lucky, theshock blast pushes him awayA lightning strike causes a transienton the power line, creating an arcbetween the meter’s input terminaland resulting in loud noises.and removes him from theproximity of the arc; thoughinjured, his life is saved. Inthe worst case, the victimis subjected to fatal burninjuries from the fierce heatof the arc or plasma blast.In addition to using a multi meter rated for the appropriatemeasurement category, anyoneworking on live power circuitsshould be protected with flameresistant clothing, should wearsafety glasses or, better yet, asafety face shield, and shoulduse insulated gloves and shoes.Then, a high current flows in theclosed circuit which is formed.An arc starts at the probe tips.12If those arcs join, theresulting high-energyarc can create a lifethreatening situationfor the user.43When you pull the probes awayas a reaction to the loud noise,arcs are drawn to the motorterminals you’re probing.Figure 2. A worst-case scenario—potential arc blast sequence.4 Fluke CorporationABCs of multimeter safety: Multimeter safety and you
Arc blastVand electric shock: Use the right high-energy fusesTEMPERATUREAmAACOMV189 TRUE RMS MULTIMETERVAAmAA10A ic shockWhile most people are aware of the dangerfrom electric shock, few realize how little current and voltage are required for a fatal shock.Current flows as low as 30 mA can be fatal (1mA 1/1000 A). Let’s look at the effects of current flow through a “typical” 68 kilogram (150pound) male: At about 10 mA, muscular paralysis of thearms occurs, so that he cannot release hisgrip. At about 30 mA, respiratory paralysisoccurs. His breathing stops and the resultsare often fatal.Figure 3. Misuse of DMM in Ammeter Mode.Transients aren’t the onlysource of possible short circuitsand arc blast hazard. One ofthe most common misuses ofhandheld multimeters can causea similar chain of events.Let’s say a user is making current measurements on signalcircuits. The procedure is toselect the amps function, insertthe leads in the mA or ampsinput terminals, open the circuitand take a series measurement. In a series circuit, currentis always the same. The inputimpedance of the amps circuitmust be low enough so that itdoesn’t affect the series circuit’s current. For instance, theinput impedance on the 10 Aterminal of a Fluke meter is .01Ω. Compare this with the inputimpedance on the voltage terminals of 10 MΩ (10,000,000 Ω).If the test leads are left inthe amps terminals and thenaccidentally connected acrossa voltage source, the low inputimpedance becomes a shortcircuit! It doesn’t matter if theselector dial is turned to volts;the leads are still physicallyconnected to a low-impedancecircuit.* That’s why the ampsterminals must be protected byfuses. Those fuses are the onlything standing between aninconvenience–blown fuses–and a potential disaster.5 Fluke CorporationUse only a multimeter withamps inputs protected by highenergy fuses. Never replacea blown fuse with the wrongfuse. Use only the high-energyfuses specified by the manufacturer. These fuses are rated at avoltage and with a short circuitinterrupting capacity designedfor your safety.Overload protectionFuses protect against overcurrent. The high input impedanceof the volts/ohms terminalsensures that an overcurrentcondition is unlikely, so fusesaren’t necessary. Overvoltageprotection, on the other hand,is required. It is provided by aprotection circuit that clampshigh voltages to an acceptablelevel. In addition, a thermalprotection circuit detects anovervoltage condition, protectsthe meter until the conditionis removed, and then automatically returns to normaloperation. The most commonbenefit is to protect the multi meter from overloads whenit is in ohms mode. In thisway, overload protection withautomatic recovery is providedfor all measurement functionsas long as the leads are in thevoltage input terminals.ABCs of multimeter safety: Multimeter safety and you At about 75 to 250 mA, for exposureexceeding five seconds, ventricular fibrillation occurs, causing incoordina tion ofthe heart muscles; the heart can no longerfunction. Higher currents cause fibrillation atless than five seconds. The results are oftenfatal.Now let’s calculate the threshold for a “hazardous” voltage. The approximate body resistanceunder the skin from hand to hand across thebody is 1000 Ω. A voltage of only 30 V across1000 Ω will cause a current flow of 30 mA.Fortunately, the skin’s resistance is muchhigher. It is the resistance of the skin, especially the outer layer of dead cells, that protectsthe body. Under wet conditions, or if there isa cut, skin resistance drops radically. At about600 V, the resistance of the skin ceases toexist. It is punctured by the high voltage.For multimeter manufacturers and users, theobjective is to prevent accidental contact withlive circuits at all costs.Look for: Meters and test leads with doubleinsulation. Meters with recessed input jacks and testleads with shrouded input connectors. Test leads with finger guards and a non-slipsurface. Meter and test leads made of high-quality,durable, non-conductive materials.* Some multimeters, such as the Fluke 80 Series, have anInput Alert which gives a warning beep if the meter is in thisconfiguration.
Work safelySafety is everyone’s responsibility but ultimatelyit’s in your hands.No tool by itself can guarantee your safety.It’s the combination of the right tools and safework practices that gives you maximum protection. Here are a few tips to help you in yourwork. Work on de-energized circuits wheneverpossible. Use proper lock-out/tag-out procedures. If these procedures are not in place ornot enforced, assume that the circuit is live. On live circuits, use protective gear:– Use insulated tools.– Wear safety glasses and arc rated faceshield if required– Wear insulated gloves; remove watchesor other jewelry.– Stand on an insulated mat.– Wear approved clothing, not ordinarywork clothes. When making measurements on live circuits:– Hook on the ground clip first, then makecontact with the hot lead. Remove the hotlead first, the ground lead last.– Hang or rest the meter if possible. Try toavoid holding it in your hands, to minimize personal exposure to the effects oftransients.– Use the three-point test method, especially when checking to see if a circuitis dead. First, test a known live circuit.Second, test the target circuit. Third, testthe live circuit again. This verifies thatyour meter worked properly before andafter the measurement.– Use the old electricians’ trick of keepingone hand in your pocket. This lessensthe chance of a closed circuit across yourchest and through your heart.Applying categories toyour workShortcuts to understandingcategoriesHere are some quick ways toapply the concept of categoriesto your every day work: The general rule-of-thumb isthat the closer you are to thepower source, the higher thecategory number, and thegreater the potential dangerfrom transients. It also follows that thegreater the short-circuit current available at a particularpoint, the higher the CATnumber. Another way of saying thesame thing is the greater thesource impedance, the lowerthe CAT number. Sourceimpedance is simply the totalimpedance, including theimpedance of the wiring,between the point where youare measuring and the powersource. This impedance iswhat dampens transients. Finally, if you have anyexperience with the application of transient voltage surgesuppression (TVSS) devices,you understand that a TVSSdevice installed at a panelmust have higher energyhandling capacity than oneinstalled right at the computer. In CAT terminology, thepanelboard TVSS is a CAT IIIapplication, and the computeris a receptacle-connectedload and therefore, a CAT IIinstallation.Multiple categoriesThere’s one scenario that sometimes confuses people trying toapply categories to real worldapplications. In a single piece ofequipment, there is often morethan one category. For example,in office equipment, from the120 V/230 V side of the powersupply back to the receptacle isCAT II. In the electronic circuitry, on the other hand, thetransient level is expected tobe one step lower. In buildingcontrol systems, such as lighting control panels, or industrialcontrol equipment such asprogrammable controllers, it iscommon to find electronic circuits (0) and power circuits (CATIII) existing in close proximity.What do you do in thesesituations? As in all real-worldsituations, use common sense.In this case, that means usingthe meter with the highercategory rating. In fact, it’s notrealistic to expect people to begoing through the categorydefining process all the time.What is realistic, and highlyrecommended, is to select amulti meter rated to the highestcategory (CAT IV) in which itcould possibly be used. In otherwords, err on the side of safety.As you can see, the conceptof categories is not new andexotic. It is simply an extension of the same common-senseconcepts that people who workwith electricity professionallyapply every day.Always wear approved personal protective equipment (PPE), including arc rated clothing,leather over rubber gloves, safety glasses, and an arc-rated face shield or hood, both withhard hat and hearing protection.6 Fluke CorporationABCs of multimeter safety: Multimeter safety and you
How to evaluate a multimeter's safetyratingUnderstanding voltage withstand ratingsIEC/EN 61010-1 test procedures take into accountthree main criteria: steady-state voltage, peakimpulse transient voltage and source impedance.These three criteria together will tell you a multimeter’s true voltage withstand value.When is 600 V more than 1000 V?MeasurementcategoryWorking voltage(dc or ac-rms toground)Peak impulsetransient (20repetitions)Test sourceΩ V/A)CAT II300 V2500 V12 Ohm source600 V4000 V12 Ohm source1000 V6000 V12 Ohm source300 V4000 V2 Ohm source600 V6000 V2 Ohm source1000 V8000 V2 Ohm source300 V6000 V2 Ohm source600 V8000 V2 Ohm source1000 V12000 V2 Ohm sourceCAT IIICAT IVTable 2 can help us understand an instrument’strue voltage withstand rating:1. Within a category, a higher “working voltage” (steady-state voltage) is associated witha higher transient, as would be expected. Forexample, a CAT III-600 V meter is tested with6000 V transients while a CAT III-1000 Vmeter is tested with 8000 V transients. So far,so good.2. What is not as obvious is the differencebetween 6000 V transient for CAT III-600V and the 6000 V transient for CAT II-1000V. They are not the same. This is where thesource impedance comes in. Ohm’s Law (Amps Volts/Ohms) tells us that the 2 Ω test sourcefor CAT III has six times the current of the 12 Ωtest source for CAT II.The CAT III-600 V meter clearly offers superiortransient protection compared to the CAT II-1000V meter, even though its so-called “voltagerating” could be perceived as being lower. It is thecombination of the steady-state voltage (called theworking voltage), and the category that determines the total voltage withstand rating of the testinstrument, including the all-important transientvoltage withstand rating.A note on CAT IV: Test values and designstandards for Category IV voltage testing areaddressed in IEC/EN 61010-1 standard.Table 2. Transient test values for measurement categories. (50 V/150 V valuesnot included.)The bottom lineIf you are faced with the taskof replacing your multimeter, doone simple task before you startshopping: Analyze the worstcase scenario of your job anddetermine what category youruse or application fits into.First choose a meter rated forthe highest category you couldbe working in. Then, look for amultimeter with a voltage ratingfor that category matching yourneeds. While you’re at it, don’tforget the test leads. IEC/EN61010-1 applies to test leadstoo: they should be certified to acategory and voltage as high orhigher than the meter. When itcomes to your personal protection, don’t let test leads be theweak link.Creepage and clearanceIn addition to being tested to an actual overvoltage transient value, multimeters are required byIEC/EN 61010-1 to have minimum creepage andclearance distances between internal componentsand circuit nodes. Creepage measures distanceacross a surface. Clearance measures distancesthrough the air. The higher the category andworking voltage level, the greater the internalspacing requirements.Look for category and voltage ratings oftest leads and multimeters.Fluke. Keeping your worldup and running. Fluke CorporationPO Box 9090, Everett, WA 98206 U.S.A.Fluke Europe B.V.PO Box 1186, 5602 BDEindhoven, The NetherlandsFor more information call:In the U.S.A. (800) 443-5853 orFax (425) 446-5116In Europe/M-East/Africa 31 (0) 40 2675 200 orFax 31 (0) 40 2675 222In Canada (800)-36-FLUKE orFax (905) 890-6866From other countries 1 (425) 446-5500 orFax 1 (425) 446-5116Web access: http://www.fluke.com 2016-2018 Fluke Corporation.Specifications subject to change without notice.Printed in U.S.A. 1/2018 6007411b-enModification of this document is not permittedwithout written permission from Fluke Corporation.7 Fluke CorporationABCs of multimeter safety: Multimeter safety and you
189 TRUE RMS MULTIMETER 400mA FUSED 10A MAX FUSED CAT 1000V ABCs of multimeter safety: Multimeter safety and you APPLICATION NOTE Meters have been used for years by technicians and electri-cians yet the fact is that meters designed to the IEC/EN 61010 standard offer a significantly hi
189 TRUE RMS MULTIMETER 400mA FUSED 10A MAX FUSED CAT 1000V ABCs of multimeter safety: Multimeter safety and you APPLICATION NOTE Meters have been used for years by technicians and electricians yet the fact is that meters designed to the IEC/EN 61010 standard offer a significantly hi
113 True RMS Multimeter 173,00 121,10 114 True RMS Multimeter 209,00 146,30 115 True RMS Multimeter 270,00 189,00 116 True RMS Multimeter 289,00 202,30 116/62MAX Kit Fluke HVAC Multimeter and IR Thermometer Combo Kit 405,00 283,50 116/323 Kit Fluke HVAC True RMS Mult
ABCs of z/OS System Programming: Volume 5 Paul Rogers Base and Parallel Sysplex, GRS, RRS, ARM, sysplex failure management System Logger, z/OS system operation GDPS, zSeries availability. International Technical Support Organization ABCs of z/OS System Programming: Volume 5 May 2011
1 Fluke Calibration 8588A Reference Multimeter / 8558A 8.5-Digit Multimeter The 8588A Reference Multimeter is the world’s most stable digitizing multi- meter. . absolute 260 50 335 65 310 100 400 129
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Upon removing your new Digital Multimeter from its packing, you should have the following items: 1. Digital Multimeter. 2. Test lead set (one black, one red). 3. Instruction Manual. 4. Protective holster. 1-2 Meter Safety Terms marked on Equipment ATTENTION — Refer to Manual. DOUBLE INSULATION — Protection Class II.
regulations and guidelines found in this booklet. The ABCs of California Boating is based upon the California Harbors and Navigation Code, Vehicle Code, Penal Code, and California Code of Regulations, but uses everyday terms rather than legal language in most instances. Not all provisions of law pertaining to boating are included.
A programming manual is also available for each Arm Cortex version and can be used for MPU (memory protection unit) description: STM32 Cortex -M33 MCUs programming manual (PM0264) STM32F7 Series and STM32H7 Series Cortex -M7 processor programming manual (PM0253) STM32 Cortex -M4 MCUs and MPUs programming manual (PM0214)
