APPLICATION NOTE ABCs Of Multimeter Safety: Multimeter .
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 overvoltagesincrease. Motors, capacitors and power conversionequipment, such as variable speed drives, can beprime generators of spikes. Lightning strikes onoutdoor transmission lines also cause extremelyhazardous high-energy transients. If you’retaking measurements on electrical systems, thesetransients are “invisible” and largely unavoidablehazards. They occur regularly on low-voltagepower circuits, and can reach peak values in themany thousands of volts. In these cases, you’redependent for protection on the safety marginalready built into your meter. The voltage ratingalone will not tell you how well that meter wasdesigned to survive high transient 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 Vlasted only a few minutes when measurements189 TRUE RMS MULTIMETERTEMPERATUREmAAA10A MAXFUSEDwere taken while the train wasoperating. A close look revealedthat the train stopping andstarting generated 10,000 Vspikes. These transientshad no mercy on earlymultimeter input circuits. Thelessons learned through thisinvestigation led to significantimprovements in multimeterinput protection circuits.Test tool safety standardsTo protect you againsttransients, safety must be builtinto the test equipment. Whatperformance specificationshould you look for, especiallyif you know that you couldbe working on high-energycircuits? The task of definingsafety standards for testequipment is addressed by theInternational ElectrotechnicalCommission (IEC). Thisorganization developsinternational safety standardsfor electrical test equipment.VCOM400mAFUSEDCAT1000VMeters have been used for yearsby technicians and electriciansyet 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 V(before electricitymeter)CAT 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 deliver largecurrents. If a transient causes an arc-over, the highcurrent can sustain the arc, producing a plasmabreakdown or explosion, which occurs when thesurrounding air becomes ionized and conductive.The result is an arc blast, a disastrous event whichcauses more electrical injuries every year thanthe better known hazard of electric shock. (See“Transients–the hidden danger” on page 4.)MeasurementcategoryIn briefThree-phase atutility connection,any outdoor mainsconductors.Expected shortcircuit currentabove 50 kA. Refers to the “origin of installation,” i.e., wherelow-voltage connection is made to utility power Electricity meters, primary overcurrentprotection equipment 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.Expected shortcircuit currentabove 10 kA up to50 kA. 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 and threephase receptacleconnected loads.Expected shortcircuit current upto 10 kA. Appliance, portable tools, and other householdand similar loads Outlet and long branch circuitsO (non-CATrated)Other circuits not Protected electronic equipmentdirectly connected Equipment connected to (source) circuits inwhich measures are taken to limit transientto MAINSovervoltages to an appropriately low level– Telecommunication circuits– Battery sourced circuits– Generator sourced auxiliary circuits, etc. Any high-voltage, low-energy source derivedfrom a high-winding resistance transformer,such as the high-voltage section of a copierMeasurement categoriesThe most important single concept to understandabout the IEC/EN 61010 standards is theMeasurement category. The standard definesCategories II through IV, often abbreviated asCAT II, CAT III, CAT IV, etc. (See Figure 1.) Thedivision of a power distribution system intocategories is based on the fact that a dangeroushigh-energy transient such as a lightningstrike will be attenuated or dampened as ittravels through the impedance (ac resistance)of the system. A higher CAT number refers toan electrical environment with higher poweravailable and higher energy transients. Thusa multimeter designed to a CAT III standard isresistant to much higher energy transients thanone designed to CAT II standards.2 Fluke CorporationExamplesCAT IVTable 1. Measurement categories. IEC/EN 61010 applies to low-voltage ( 1000 V)test equipment.ABCs of multimeter safety: Multimeter safety and you
Within a category, a higher voltage ratingdenotes a higher transient withstand rating, e.g.,a CAT III-1000 V meter has superior protectioncompared to a CAT III-600 V rated meter. Thereal misunderstanding occurs if someone selectsa CAT 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, nottransients and arc blast. Shocks, which will bediscussed later, can be every bit as lethal asarc blast.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 technicallyCAT IV. Why? Any outdoor conductor is subjectto very 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 InstallationCategories, the rules of real estate apply: it’slocation, location, location. (For more discussion ofInstallation Categories, see page 6, “Applying categories toyour work.”)Independent testing is the key tosafety complianceLook for a symbol and listing number of an independent testinglab such as UL, CSA, VDE, TÜV or other recognized testingorganization. Beware of wording such as “Designed to meetspecification .” Designer’s plans are never a substitute for anactual 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 possiblefor a manufacturer to self-certify that its meter is CAT II orCAT III without any independent verification. The IEC developsand proposes standards, but it is not responsible for enforcingthe standards.Look for the symbol and listing number of an independenttesting lab such as UL, CSA, VDE, TÜV or other recognizedapproval agency. That symbol can only be used if the productsuccessfully completed testing to the agency’s standard, whichis based on national/international standards. UL 61010-1, forexample, is based on IEC/EN 61010-1. In an imperfect world,that is the closest you can come to ensuring that the multimeteryou choose 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 bythe European Commission and mandated through the use of“directives.” There are directives affecting many product types,and products from outside the European Union can not beimported and sold there if they do not comply with applicableEuropean directives. Compliance with the directive can beachieved by proving conformance to a relevant technicalstandard, such as IEC/EN 61010-1 for low-voltage products.Manufacturers are permitted to self-certify that they havemet the standards, issue their own Declaration of Conformity,and mark the product “CE.” The CE mark is not, therefore, aguarantee of independent testing.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 thiscircuits. 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 ona proving 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 absenceof voltage.
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 preventthis event fail. Perhaps it is not a CAT III orCAT IV rated meter. The result is a direct shortbetween the two measurement terminalsthrough the meter and the test leads.2. A high-fault current–possibly severalthousands of amps–flows in the short circuitjust created. 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 atempera-ture approaching6000 C, which is higherthan the temperature ofan oxyacetylene cuttingtorch! As the arc grows, fedby available short circuitcurrent, it superheats thesurrounding air. Both ashock blast and a plasmafireball are created. If thetechnician is lucky, theA lightning strike causes a transienton the power line, creating an arcbetween the meter’s input terminaland resulting in loud noises.shock blast pushes him awayand 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 amulti meter rated for theappropriate measurementcategory, anyone working onlive power circuits should beprotected with flame resistantclothing, should wear safetyglasses or, better yet, a safetyface shield, and should useinsulated 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 littlecurrent and voltage are required for a fatalshock. Current flows as low as 30 mA can befatal (1 mA 1/1000 A). Let’s look at the effectsof current flow through a “typical” 68 kilogram(150 pound) male: At about 10 mA, muscular paralysis of thearms occurs, so that he cannot releasehis grip. 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 only sourceof possible short circuits and arcblast hazard. One of the mostcommon misuses of handheldmultimeters can cause a similarchain of events.Let’s say a user is making currentmeasurements on signal circuits.The procedure is to selectthe amps function, insert theleads in the mA or amps inputterminals, open the circuit andtake a series measurement. In aseries circuit, current is alwaysthe same. The input impedanceof the amps circuit must be lowenough so that it doesn’t affectthe series circuit’s current. Forinstance, the input impedanceon the 10 A terminal of a Flukemeter is .01 Ω. Compare thiswith the input impedance onthe 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–anda potential disaster.5 Fluke CorporationUse only a multimeter with ampsinputs protected by high-energyfuses. Never replace a blown fusewith the wrong fuse. Use onlythe high-energy fuses specifiedby the manufacturer. These fusesare rated at a voltage and with ashort circuit interrupting capacitydesigned for your safety.Overload protectionFuses protect againstovercurrent. The high inputimpedance of the volts/ohms terminals ensures thatan overcurrent conditionis unlikely, so fuses aren’tnecessary. Overvoltageprotection, on the other hand,is required. It is provided by aprotection circuit that clampshigh voltages to an acceptablelevel. In addition, a thermalprotection circuit detectsan overvoltage condition,protects the meter until thecondition is removed, and thenautomatically returns to normaloperation. The most commonbenefit is to protect themulti meter from overloadswhen it 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, ventricularfibrillation occurs, causing incoordina tion ofthe heart muscles; the heart can no longerfunction. Higher currents cause fibrillationat less than five seconds. The results areoften fatal.Now let’s calculate the threshold for a“hazardous” voltage. The approximate bodyresistance under the skin from hand to handacross the body is 1000 Ω. A voltage of only30 V across 1000 Ω will cause a current flowof 30 mA. Fortunately, the skin’s resistanceis much higher. It is the resistance of theskin, especially the outer layer of dead cells,that protects the body. Under wet conditions,or if there is a cut, skin resistance dropsradically. At about 600 V, the resistance ofthe skin ceases to exist. It is punctured by thehigh voltage.For multimeter manufacturers and users, theobjective is to prevent accidental contact withlive circuits at all costs.Look for: Meters and test leads with double insulation. Meters with recessed input jacks and testleads with shrouded input connectors. Test leads with finger guards and anon-slip surface. 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 inthis configuration.
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 andsafe work practices that gives you maximumprotection. Here are a few tips to help you inyour work. Work on de-energized circuits wheneverpossible. Use proper lock-out/tag-outprocedures. If these procedures are notin place or not enforced, assume that thecircuit 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. Tryto avoid holding it in your hands, tominimize personal exposure to the effectsof transients.– Use the three-point test method,especially when checking to see if acircuit is dead. First, test a known livecircuit. Second, test the target circuit.Third, test the live circuit again. Thisverifies that your meter worked properlybefore and after 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-thumbis that the closer you are tothe power source, the higherthe category number, and thegreater the potential dangerfrom transients. It also follows that thegreater the short-circuitcurrent available at aparticular point, the higherthe CAT number. 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 theapplication of transientvoltage surge suppression(TVSS) devices, youunderstand that a TVSSdevice installed at apanel must have higherenergy-handling capacitythan one installed rightat the computer. In CATterminology, the panelboardTVSS is a CAT III application,and the computer is areceptacle-connected loadand therefore, a CAT IIinstallation.Multiple categoriesThere’s one scenario thatsometimes confuses peopletrying to apply categories toreal world applications. In asingle piece of equipment,there is often more than onecategory. For example, inoffice equipment, from the120 V/230 V side of the powersupply back to the receptacleis CAT II. In the electroniccircuitry, on the other hand, thetransient level is expected tobe one step lower. In buildingcontrol systems, such as lightingcontrol panels, or industrialcontrol equipment such asprogrammable controllers, itis common to find electroniccircuits (0) and powercircuits (CAT III) existing inclose 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 extensionof 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'ssafety ratingUnderstanding 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 amultimeter’s true voltage withstand value.When is 600 V more than 1000 V?MeasurementcategoryWorking voltage(dc or ac-rmsto ground)Peak impulsetransient(20 repetitions)Test source(Ω 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 with ahigher 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-600 Vand the 6000 V transient for CAT II-1000 V.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 offerssuperior transient protection compared tothe CAT II-1000 V meter, even though itsso-called “voltage rating” could be perceivedas being lower. It is the combination of thesteady-state voltage (called the working voltage),and the category that determines the totalvoltage withstand rating of the test instrument,including the all-important transient voltagewithstand 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,do one simple task before youstart shopping: Analyze theworst-case scenario of your joband determine what categoryyour use 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 leadsLook for category and voltage ratings oftest leads and multimeters.too: they should be certifiedto a category and voltageas high or higher than theFluke. Keeping your worldmeter. When it comes to yourup and running. personal protection, don’t lettest leads be the weak link.Fluke Europe B.V.Creepage and clearanceIn addition to being tested to an actualovervoltage transient value, multimeters arerequired by IEC/EN 61010-1 to have minimumcreepage and clearance distances betweeninternal components and circuit nodes. Creepagemeasures distance across a surface. Clearancemeasures distances through the air. The higherthe category and working voltage level, thegreater the internal spacing requirements.P.O. Box 11865602 BD EindhovenThe NetherlandsWeb: www.fluke.co.ukFor more information call:In Europe/M-East/Africa 31 (0)40 267 5100 orFax 31 (0)40 267 5222Fluke (UK) Ltd.52 Hurricane WayNorwich, NorfolkNR6 6JBUnited KingdomTel.: 44 (0) 20 7942 0700Fax: 44 (0) 20 7942 0701E-mail: industrial@uk.fluke.nlWeb: www.fluke.co.uk 2016 Fluke Corporation. All rights reserved.Data subject to alteration without notice.05/2016 6007411a-ukenModification 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 electricians 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 electri-cians yet the fact is that meters designed to the IEC/EN 61010 standard offer a significantly hi
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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
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.
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GRAPHING MULTIMETER A . graphing multimeter, abbreviated . GMM, is a cross between a digital meter and a digital storage oscilloscope. A graphing multimeter displays the voltage levels on a display and a digital readout. FI
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