electrical measurement equipments

8/11/2019 Electrical Measurement equipments

1/51

2003 Fluke Corporation Electrical measurement safety 1

Electrical measurement safety

Understanding hiddenhazards and new safetystandards


2/51


Goals

Awareness of electrical measurement hazards

Understand international safety specifications for DMMs andscopes

Understand the four installation overvoltage categories

Learn how to minimize and avoid electrical measurement hazardsOutline

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

Goals of this education program


3/51


Handheld test tool safety

Last known earthlyresidence ofautomotive fuseused to replaceoriginal fuse

Test leads survived intact

How not to save time...


4/51



Test leads destroyed13.8 kVarcedover totestprobes.

Insides were barbecued.

This DMM had a hot date with 13.8 kV.


5/51



Probe tipsburned off

250V fusedidntopen intime

The wrong meter to use on a power circuit.

Poor quality leads andprobes led to injury.


6/51



The electrician suffered severe burn

injuries on his hand and arm.

Fingerprints burnedinto probes


7/51



Typical work environment


8/51



Aftermath of an accident


9/51



If it melts metal, what does it do to people?


10/51


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 meters volt rating

Measuring voltage with test leads in current jacks

Protection: High energy fuses rated to the meters 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 III1000 V. Replace when damaged

Using meter or tester above rated voltage

Protection:Good karma

Common DMM / tester hazards


11/51


Three common errors that are avoidable

Common DMM safety hazards

Measuring voltage while testleads 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 meters

rated voltage. Using meter above rated voltage, i.e., on medium

voltage circuits.

Protection:Good karma


12/51


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 singletest 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 endconnectors

Probe tips: not loose or broken off

Safety inspection

Test leads and probes


13/51


Safety inspection

Step 1: Plug test lead in V/ input. Select .

Step 2: Insert probe tip into mA input. Read value.

Step 3: Insert probe tip into A input. Read value.

Is the fuse okay? What would an open fuse read?

Checking meter fuses on most meters


14/51


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 mV

Step 3: Select Step 4: Select A.

Overload protection is only to DMMs rated voltage.

Overload protection on volts inputs

Safety Inspection


15/51


New IEC Safety Standards


16/51


International Electrotechnical Commission

IEC 61010 is the new standard for low voltagetest, measurement and control equipment.

IEC 61010 provides much improved protectionagainst overvoltage impulse transients -voltage spikes.

IEC 61010 is the basis for:

ANSI/ISA-S82.01-94 (US)

CAN C22.2 No. 1010.1-92 (CAN)

EN61010-1:1993 (EUR)


17/51


IEC 61010 key concepts

CATEGORIES: CAT I to CAT IV

The greatest danger from transients is inthe high categories, because they couldtrigger an arc blast.

IMPULSE TESTING: No failure allowed Meters must be tested by being hit with a

specified number of transients, withspecified peak voltages.

INTERNAL SPACING: increased

Clearance (distance through the air) and

Creepage (surface distance) are increased.

Protection against overvoltage transients


18/51


Overvoltage category

The level and energy of voltage impulses is

dependent on the location. The closer the locationis to the power source, the higher the available faultcurrent, 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


19/51


Category locations


20/51


Common sense ways to think of categories

Overvoltage category

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 thecategory

Transients are dampened by system impedance asthey travel from the point where they were generated.

TVSS (transient voltage surge suppression)

devices are sized larger (more joules) at thepanel than at the receptacle outlet.


21/51


Determining the true voltagewithstand 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 IV600 V: 8 kV impulse

CAT III example:

CAT III600 V: 6 kV impulse

CAT III1000 V: 8 kV impulse

CAT II example:

CAT II600 V: 4 kV impulse

CAT II1000 V: 6 kV impulse


22/51


When is 600 V more than 1000 V?

CAT III-600 V or CAT II-1000 V?

The greater the source impedance,the lowerthe Category:

CAT IV-600 V:

8 kV impulse

CAT III-600 V:

6 kV impulse

2 ohm test source

CAT II-1000 V:

6 kV impulse

12 ohm test source

A CAT III-600 V 6k V test impulse has 6 times thecurrentof a CAT II-1000 V 6 kV test impulse!


23/51


First the CAT, then the voltage

Voltage rating by itself can be misleading.

CAT III-1000 V (8 kV transient) is safer than CAT III-600 V(6k V transient)

But CAT III-600 V is safer than CAT II-1000 V

First know the category you are working in, then choosethe appropriate voltage rating.

If you ever measure power circuits, you should usea 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.


24/51


CAT III-600 V

CAT III-1000 V

CAT IV-600 VCAT III-1000 V

Look for CAT III or CAT IV markings


25/51


Levels of CAT III protection

CAT Transient with Fuse and Clearance Creepage2 Source overload (air) (surface)

Rating

III-1000 V 8000 V 1000 V 16.0 mm 16.0 mm

IV-600 V

III-600 V 6000 V 1000 V 11.5 mm 14.0 mm

II-1000 V

II-600 V 6000 V 600 V 11.5 mm 11.5 mm


26/51


IEC sets standards but does not test or inspect

for compliance.A manufacturer can claim to design to astandard with no independent verification.

To be UL-Listed, CSA or TUV-Certified , a

manufacturer must employ the listing agency toTEST the products compliance with the standard.

Look for the listing agencys emblem on the meter.

Listed vs. designed to


27/51


Brand A Brand B Brand C

Markings CAT II750 V CAT III D of C to1000 V Input IEC 1010-1

CAT II1000 V Cat III1000 V CAT III1000 V

Creepageclearance

3.7 mm 2.5 mm 7.5 mmDoesnt Doesnt Doesntcomply comply comply

with 5.7 mm with 16 mm with 16 mm

Transienttests

Input protection Display Input protectioncomponents window components

opened breakdown openedunder high @ CAT II level

voltage

Tested @

But can the product pass testing...

Designed to IEC 1010-1


28/51


1 Flashover inside meter

3 Arcing at the terminals 4Arc blast

2 Fault current in test leads


29/51


Misuse of DMM in ammeter mode


30/51


Fuse protection on amps inputs


31/51



Whats 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 voltagerating marked near the input jacks.

CAT or voltage rating alone can bemisleading

Look for independent certification.UL 3111


32/51



If you use a scope on power

circuits, you need a CAT III-600 Vscope and scope probes.

Look for the CAT rating and voltagerating marked near the input jacks.

CAT III-600 V


33/51


CAT IV-600 V

CAT III-1000 V


Safety must be built-in

An industrial grade meter devotes10 % - 15 % of components exclusivelyto protection.

Built-in protection against the mostcommon safety hazards:

High voltage transients and dangerof arc-over

Voltage contact while in continuityor resistance mode

High integrity components

Voltage measurement while test leads areplugged into amps jacks

High energy fuses

Overload protectionon all functions

1000V high

energy fuses


34/51


Unless a meter was specifically designed to

meet CAT III-600 V or higher, it is not safeto useon power circuits. Most meters produced before

1997 do not meet the standard.

Older Fluke70 Series-IIICAT II-600 V

UNDER RATED

New170 Series


Original

Fluke 70 Series

NOT RATED

Newer meters also have

additional features and

capabilities

Larger displays

Back light

1000 Vac capability

Capacitance

Frequency

Magnetic hangers

Temperature

3X dc accuracy

2X ac accuracy

Min / Max Record

Probe holders

Battery door

What about my old meter?


35/51


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.


36/51


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 onpower circuits.

Use replacement fuses approved by the

manufacturer.


37/51


Test lead safety checklist

Dont 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 usingspecialized probes and PPE materials

Finger guards

Insulation not damaged: not melted, cut,cracked, stretched

Connectors: no insulation pulled awayfrom end connectors

Probe tips: not loose or broken off (too short)


38/51


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. Dont work alone.

Practice safe measurement techniques.

Always connect the grounded lead first, hot second.

Disconnect the hot lead first, grounded lead second. Use the three-point test method.

Test known circuit, measure target circuit,then re-test known circuit.


39/51


Oscilloscope safety

Category ratings

Select a scope and probesand clamps for the worstcase category

Voltage ratings

Working voltage

Transient voltage

Overvoltage Working voltage Peak impulse Test source

category (dc or acrms to grnd) transient (Ohm = V/A)

(20 repetitions)

CAT I 600V 2500 V 30 ohm source

CAT I 1000V 4000 V 30 ohm source

CAT II 600V 4000 V 12 ohm source

CAT II 1000V 6000 V 12 ohm source

CAT III 600V 6000 V 2 ohm source

CAT III 1000V 8000 V 2 ohm source


40/51


Oscilloscope safety

Line powered bench scopes

Use a differential or isolation probeto separate the earth groundconnection of the scope from highenergy circuits that are alsoreferenced to earth ground.

Isolate bench scope grounds onlyin conjunction withdifferential/isolation probes.

DifferentialInput

+

50 BNCOutput


41/51


Typical use of a differential probe

Oscilloscope safety

Typical use of a differential probe

DC VOLTAGE

DC VOLTAGE

TO MOTOR


42/51


Oscilloscope safety

Battery powered scopes -

Have inherent ground isolation for superiorcommon mode noise rejection

Some come standard with CAT III 600 volt probesfor measurements in high energy circuits


43/51


Oscilloscope safety

Probes

Beware of bench scope probes - they are usuallyCAT I - 500 volts

Dont use CAT I or II divider probes on CAT III circuits

Dont use probes with exposed metal parts

Dont use probes without specified ratings

Read the manual for safe probe connections - theymay vary greatly between instruments


44/51


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 revealdangerous 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


45/51


CAT III circuits - Make sure

you use Cat III leads AND

scope AND current clamp

Oscilloscope safety

Current clamps

Clamps have category and working voltage ratings

Do not exceed them


46/51


CAT III-600 V


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 loadsthat plug into a receptacle outlet.


47/51


Equipment of overvoltage category IVis 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 pump22

CAT IV


48/51


Premises wiring: mainscircuits, 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 notinclude receptacle plug-in

loads, except in the case of heavy

appliance outlets with short

connections to service entrance

CAT III


49/51


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

CAT II


50/51


Equipment in which measures aretaken to limit transient overvoltagesto an appropriately low level

Examples are protected electronic

circuits. A copier that has an internalstep-up transformer and 1000 Vdc is stilla CAT I-1000 V machine, because thecurrent levels are so low

CAT I


51/51

electrical measurement equipments

Documents