Electrical measurement safety Understanding hidden hazards and new

Electrical measurement safety Understanding hidden hazards and new safety standards © 2003 Fluke Corporation Electrical measurement safety 1

Goals of this education program Goals • Awareness of electrical measurement hazards • Understand international safety specifications for DMMs and scopes • Understand the four installation overvoltage categories • Learn how to minimize and avoid electrical measurement hazards Outline • What electrical power can do to a DMM • Common safety hazards • Meter safety inspection • IEC Safety Standards • Arc blast • Meter and scope safety check list © 2003 Fluke Corporation Electrical measurement safety 2

Handheld test tool safety How not to save time. . . Last known earthly residence of automotive fuse used to replace original fuse Test leads survived intact © 2003 Fluke Corporation Electrical measurement safety 3

Handheld test tool safety This DMM had a hot date with 13. 8 k. V arced over to test probes. Test leads destroyed Insides were barbecued. © 2003 Fluke Corporation Electrical measurement safety 4

Handheld test tool safety The wrong meter to use on a power circuit. 250 V fuse didn’t open in time Probe tips burned off © 2003 Fluke Corporation Electrical measurement safety Poor quality leads and probes led to injury. 5

Handheld test tool safety The electrician suffered severe burn injuries on his hand arm. Fingerprints burned into probes © 2003 Fluke Corporation Electrical measurement safety 6

Handheld test tool safety Typical work environment © 2003 Fluke Corporation Electrical measurement safety 7

Handheld test tool safety Aftermath of an accident © 2003 Fluke Corporation Electrical measurement safety 8

Handheld test tool safety If it melts metal, what does it do to people? © 2003 Fluke Corporation Electrical measurement safety 9

Common DMM / tester hazards • Arc from transients (lightning, load switching) Protection: Independent certification to meet CAT III-1000 V or CAT IV 600 V • Voltage contact while in continuity or resistance Protection: Overload protection in OHMs up to the meter’s volt rating • Measuring voltage with test leads in current jacks Protection: High energy fuses rated to the meter’s voltage rating Use meters / testers without current jacks • Shock from accidental contact with live components Protection: Test Leads double insulated, recessed / shrouded, finger guards, CAT III – 1000 V. Replace when damaged • Using meter or tester above rated voltage Protection: Good karma © 2003 Fluke Corporation Electrical measurement safety 10

Common DMM safety hazards Three common errors that are avoidable • Measuring voltage while test leads are in the current jacks: short-circuit! Protection: Fluke meters use high energy fuses. • Contact with ac or dc power source while in Ohms mode. Protection: Use a meter with “Overload Protection”. Functions are self-protected to the meter’s rated voltage. • Using meter above rated voltage, i. e. , on medium voltage circuits. Protection: Good karma © 2003 Fluke Corporation Electrical measurement safety 11

Safety inspection Test leads and probes Check test lead resistance: Step 1: Insert leads in V/ and COM inputs. Step 2: Select , touch probe tips. Good leads are 0. 1 - 0. 3 . How do you check a single test lead? Visually check for: • • • CAT III-1000 V/CAT IV-600 V rating Double insulation Shrouded connectors, finger guards Insulation not melted, cut, cracked, etc. Connectors not damaged: no insulation pulled away from end connectors • Probe tips: not loose or broken off © 2003 Fluke Corporation Electrical measurement safety 12

Safety inspection Checking meter fuses on most meters Step 1: Plug test lead in V/ input. Select . Step 2: Insert probe tip into m. A input. Read value. Step 3: Insert probe tip into A input. Read value. Is the fuse okay? What would an open fuse read? © 2003 Fluke Corporation Electrical measurement safety 13

Safety Inspection Overload protection on volts inputs With leads in V/ and COM inputs: Step 1: Select V and put probes in a live outlet. Will you damage the meter if you. . . Step 2: Select m. V Step 3: Select Step 4: Select A. Overload protection is only to DMM’s rated voltage. © 2003 Fluke Corporation Electrical measurement safety 14

New IEC Safety Standards © 2003 Fluke Corporation Electrical measurement safety 15

International Electrotechnical Commission • IEC 61010 is the new standard for low voltage “test, measurement and control equipment”. • IEC 61010 provides much improved protection against “overvoltage impulse transients” voltage spikes. • IEC 61010 is the basis for: • ANSI/ISA-S 82. 01 -94 (US) • CAN C 22. 2 No. 1010. 1 -92 (CAN) • EN 61010 -1: 1993 (EUR) © 2003 Fluke Corporation Electrical measurement safety 16

IEC 61010 key concepts Protection against overvoltage transients • CATEGORIES: CAT I to CAT IV • The greatest danger from transients is in the high categories, because they could trigger an arc blast. • IMPULSE TESTING: No failure allowed • Meters must be tested by being hit with a specified number of transients, with specified peak voltages. • INTERNAL SPACING: increased • Clearance (distance through the air) and • Creepage (surface distance) are increased. © 2003 Fluke Corporation Electrical measurement safety 17

Overvoltage category • The level and energy of voltage impulses is dependent on the location. The closer the location is to the power source, the higher the available fault current, the higher the category • IEC 61010 defines four locations or categories: CAT IV “Origin of installation” Utility level and any outside cable run CAT III Distribution wiring, including “mains” bus, feeders and branch circuits; permanently installed loads. CAT II Receptacle outlet circuit; plug-in loads. CAT I Protected electronic circuits © 2003 Fluke Corporation Electrical measurement safety 18

Category locations © 2003 Fluke Corporation Electrical measurement safety 19

Overvoltage category Common sense ways to think of categories • The higher the short circuit fault current available, the higher the category • High energy transients are much more dangerous, because they can trigger an arc blast • The greater the source impedance, the lower the category • Transients are dampened by system impedance as they travel from the point where they were generated. • TVSS (transient voltage surge suppression) devices are sized larger (more joules) at the panel than at the receptacle outlet. © 2003 Fluke Corporation Electrical measurement safety 20

Determining the true voltage withstand rating WITHIN each Category: • There are designated “working voltages” (50, 150, 300, 600, 1000 V). • A higher voltage has a higher transient withstand • CAT IV example: CAT IV – 600 V: 8 k. V impulse • CAT III example: CAT III – 600 V: 6 k. V impulse CAT III – 1000 V: 8 k. V impulse • CAT II example: CAT II – 600 V: 4 k. V impulse CAT II – 1000 V: 6 k. V impulse © 2003 Fluke Corporation Electrical measurement safety 21

When is 600 V more than 1000 V? • CAT III-600 V or CAT II-1000 V? • The greater the source impedance, the lower the Category: • CAT IV-600 V: • 8 k. V impulse • CAT III-600 V: • 6 k. V impulse • 2 ohm test source • CAT II-1000 V: • 6 k. V impulse • 12 ohm test source • A CAT III-600 V 6 k V test impulse has 6 times the current of a CAT II-1000 V 6 k. V test impulse! © 2003 Fluke Corporation Electrical measurement safety 22

First the CAT, then the voltage • Voltage rating by itself can be misleading. • CAT III-1000 V (8 k. V transient) is safer than CAT III-600 V (6 k V transient) • But CAT III-600 V is safer than CAT II-1000 V • First know the category you are working in, then choose the appropriate voltage rating. • If you ever measure power circuits, you should use a CAT III-600 V or CAT IV 600 V/CAT III-1000 V meter. • And CAT IV 600 V/CAT III-1000 V test leads and probes. © 2003 Fluke Corporation Electrical measurement safety 23

Look for CAT III or CAT IV markings CAT III 1000 V © 2003 Fluke Corporation CAT IV-600 V CAT III-1000 V Electrical measurement safety CAT III 600 V 24

Levels of CAT III protection CAT Transient with 2 Source Fuse and overload Rating III-1000 V IV-600 V 8000 V 16. 0 mm III-600 V II-1000 V 6000 V 11. 5 mm 14. 0 mm II-600 V 11. 5 mm © 2003 Fluke Corporation Electrical measurement safety Clearance Creepage (air) (surface) 25

“Listed” vs. “designed to” IEC sets standards but does not test or inspect for compliance. 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. © 2003 Fluke Corporation Electrical measurement safety 26

“Designed to IEC 1010 -1” But can the product pass testing. . . Brand A Brand B Brand C Markings CAT II – 750 V Tested @ CAT II – 1000 V CAT III 1000 V Input Cat III – 1000 V D of C to IEC 1010 -1 CAT III – 1000 V Creepage clearance 3. 7 mm Doesn’t comply with 5. 7 mm 2. 5 mm Doesn’t comply with 16 mm 7. 5 mm Doesn’t comply with 16 mm Input protection components opened Display window breakdown under high voltage Input protection components opened @ CAT II level Transient tests © 2003 Fluke Corporation Electrical measurement safety 27

1 Flashover inside meter 2 Fault current in test leads 3 Arcing at the terminals 4 Arc blast © 2003 Fluke Corporation Electrical measurement safety 28

Misuse of DMM in ammeter mode © 2003 Fluke Corporation Electrical measurement safety 29

Fuse protection on amps inputs © 2003 Fluke Corporation Electrical measurement safety 30

What’s the bottom line? • If you work on power circuits, you need a CAT III-600 V or CAT IV-600 V/ CAT III 1000 V meter. • Look for the CAT rating and voltage rating marked near the input jacks. • CAT or voltage rating alone can be misleading • Look for independent certification. UL 3111 CAT IV-600 V CAT III-1000 V © 2003 Fluke Corporation Electrical measurement safety 31

What’s the bottom line? • If you use a scope on power circuits, you need a CAT III-600 V scope and scope probes. CAT III-600 V • Look for the CAT rating and voltage rating marked near the input jacks. © 2003 Fluke Corporation Electrical measurement safety 32

What’s the bottom line? Safety must be built-in Overload protection • An industrial grade meter devotes on all functions 10 % - 15 % of components exclusively to protection. • Built-in protection against the most common safety hazards: • High voltage transients and danger of arc-over • Voltage contact while in continuity or resistance mode • High integrity components • Voltage measurement while test leads are plugged into amps jacks • High energy fuses © 2003 Fluke Corporation Electrical measurement safety 1000 V high energy fuses CAT IV-600 V CAT III-1000 V 33

What about my old meter? Unless a meter was specifically designed to meet CAT III-600 V or higher, it is not safe to use on power circuits. Most meters produced before 1997 do not meet the standard. Newer meters also have additional features and capabilities Larger displays Back light 1000 Vac capability Capacitance Frequency Magnetic hangers Temperature 3 X dc accuracy 2 X ac accuracy Original Fluke 70 Series NOT RATED Older Fluke 70 Series-III CAT II-600 V UNDER RATED © 2003 Fluke Corporation New 170 Series CAT IV-600 V CAT III-1000 V Electrical measurement safety Min / Max Record Probe holders Battery door 34

Meter safety checklist Insist on these safety features: • Fused current inputs (high energy fuses). • Overload protection on the ohms function. • Test leads that have shrouded connectors and finger guards. • Recessed input jacks. • Meet the latest safety standards (CAT III-600 V or CAT IV 600 V/CAT III 1000 V) and are independently certified. © 2003 Fluke Corporation Electrical measurement safety 35

Meter safety checklist Watch for: • Cracked or oily case • Broken input jacks No meter is safe when improperly used. • Use meters within their rating. • Use meters designed for measurements on power circuits. • Use replacement fuses approved by the manufacturer. © 2003 Fluke Corporation Electrical measurement safety 36

Test lead safety checklist Don’t let test leads be a weak point • CAT III-1000 V or CAT IV 600 V/ CAT III 1000 V rating • Double insulation • Shrouded connectors • Arc Flash Hazard consideration using specialized probes and PPE materials • Finger guards • Insulation not damaged: not melted, cut, cracked, stretched • Connectors: no insulation pulled away from end connectors • Probe tips: not loose or broken off (too short) © 2003 Fluke Corporation Electrical measurement safety 37

Safety first Safe practices include but are not limited to: • Whenever possible, work on de-energized circuits. Follow proper lock-out/tag-out procedures. • Use well maintained tools and appropriate safety gear • Safety glasses, insulated tools, insulating gloves, flash suits, insulating mats, etc. • Don’t work alone. • Practice safe measurement techniques. • Always connect the grounded lead first, hot second. • Disconnect the hot lead first, grounded lead second. • Use three-point test method. • Test known circuit, measure target circuit, then re-test known circuit. © 2003 Fluke Corporation Electrical measurement safety 38

Oscilloscope safety Category ratings • Select a scope and probes and clamps for the worst case category Voltage ratings • Working voltage • Transient voltage Overvoltage category © 2003 Fluke Corporation Working voltage (dc or ac – rms to grnd) Peak impulse transient (20 repetitions) Test source (Ohm = V/A) CAT I 600 V 2500 V 30 ohm source CAT I 1000 V 4000 V 30 ohm source CAT II 600 V 4000 V 12 ohm source CAT II 1000 V 6000 V 12 ohm source CAT III 600 V 6000 V 2 ohm source CAT III 1000 V 8000 V 2 ohm source Electrical measurement safety 39

Oscilloscope safety Line powered bench scopes • Use a differential or isolation probe to separate the earth ground connection of the scope from high energy circuits that are also referenced to earth ground. • Isolate bench scope grounds only in conjunction with differential/isolation probes. + Differential Input 50Ω BNC Output – © 2003 Fluke Corporation Electrical measurement safety 40

Oscilloscope safety DC VOLTAGE TO MOTOR DC VOLTAGE Typical use of a differential probe © 2003 Fluke Corporation Electrical measurement safety 41

Oscilloscope safety Battery powered scopes • Have inherent ground isolation for superior common mode noise rejection • Some come standard with CAT III 600 volt probes for measurements in high energy circuits © 2003 Fluke Corporation Electrical measurement safety 42

Oscilloscope safety Probes • Beware of bench scope probes - they are usually CAT I - 500 volts • Don’t use CAT I or II divider probes on CAT III circuits • Don’t use probes with exposed metal parts • Don’t use probes without specified ratings • Read the manual for safe probe connections - they may vary greatly between instruments © 2003 Fluke Corporation Electrical measurement safety 43

Oscilloscope safety Safe practices • De-energize circuits • Use protective gear • Do not exceed instrument voltage and category ratings • Use dc coupling - ac coupling may not reveal dangerous voltages • Use 3 -point test method • Test known live circuit • Test target circuit • Test known live circuit again • Avoid holding or touching the scope if possible © 2003 Fluke Corporation Electrical measurement safety 44

Oscilloscope safety Current clamps • Clamps have category and working voltage ratings • Do not exceed them CAT III circuits - Make sure you use Cat III leads AND scope AND current clamp © 2003 Fluke Corporation Electrical measurement safety 45

What’s the bottom line? • If you use a scope on power circuits, you need a CAT III-600 V scope and scope probes. • CAT II scopes and probes are mainly for loads that plug into a receptacle outlet. CAT III-600 V © 2003 Fluke Corporation Electrical measurement safety 46

CAT IV Equipment of overvoltage category IV is for use at the origin of the installation (utility service). • Outside and service entrance • Service drop from pole to building • Run between meter and panel • Overhead line to detached building • Underground line to well pump 22 © 2003 Fluke Corporation Electrical measurement safety 47

CAT III • Premises wiring: “mains”circuits, i. e. , bus and feeders and distribution panels • Permanently installed loads: motors, lighting systems, drives, load centers • Typically separated from utility service by at least a single level of transformer isolation • Does not include receptacle plug-in loads, except in the case of heavy appliance outlets with “short” connections to service entrance © 2003 Fluke Corporation Electrical measurement safety 48

CAT II Loads that plug in at receptacle outlet • Examples of such equipment are appliances, portable tools and other household and similar loads • All outlets at more than 10 m (30 ft) from Category III • All outlets at more than 20 m (60 ft) from Category IV © 2003 Fluke Corporation Electrical measurement safety 49

CAT I Equipment in which measures are taken to limit transient overvoltages to an appropriately low level Examples are protected electronic circuits. A copier that has an internal step-up transformer and 1000 Vdc is still a CAT I-1000 V machine, because the current levels are so low © 2003 Fluke Corporation Electrical measurement safety 50