HB 187-2006 Guide to selecting a safe multimeter by SAIGlobalAPAC

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HB
                                                                                                                                       HB 187—2006
                                                                                                Guide to Selecting a Safe Multimeter
                                                                                                                                                              HB 187—2006




                                                                                           Handbook
This is a free 6 page sample. Access the full version at http://infostore.saiglobal.com.




                                                                                           Guide to selecting a safe multimeter




                                                                                           First published as HB 187—2006.




                                                                                           COPYRIGHT
                                                                                           © Standards Australia
                                                                                           All rights are reserved. No part of this work may be reproduced or copied in any form or by
                                                                                           any means, electronic or mechanical, including photocopying, without the written
                                                                                           permission of the publisher.
                                                                                           Published by Standards Australia, GPO Box 476, Sydney, NSW 2001, Australia
                                                                                           ISBN 0 7337 7705 8
                                                                                           HB 187—2006                                                    2




                                                                                                                                              INTRODUCTION

                                                                                                This Handbook was prepared by Standards Australia with the assistance of technical
                                                                                                committee EL-049, Safety of Electrical Equipment for Measurement and Laboratory Use,
                                                                                                following concerns relating to the lack of public and industry awareness of AS 61010.1, Safety
                                                                                                of electrical equipment for measurement, control and laboratory use, and a poor
                                                                                                understanding of safety specifications when purchasing electrical test and measuring
                                                                                                equipment (such as digital multimeters, clamp meters, oscilloscopes, insulation testers and
                                                                                                similar equipment).

                                                                                                The objective of this Handbook is to provide for all users a basic understanding of the
                                                                                                important safety criteria which are specified in AS 61010.1. The Australian marketplace
                                                                                                provides a wide variety of test and measuring equipment that has been designed and
                                                                                                manufactured to many differing safety specifications with a broad range in price and quality.
                                                                                                This can be very confusing for users.
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                                                                                                Users need to consider the following questions:
                                                                                                •        How important is a well-designed and manufactured meter for your safety?
                                                                                                •        How do you know if this meter is safe for the intended use?
                                                                                                •        How important is verification testing by an independent testing laboratory?
                                                                                                This Handbook is arranged in two parts—

                                                                                                Part 1 provides basic information.
                                                                                                Part 2 provides further information that would suit technical/professional users.

                                                                                                Standards Australia acknowledges the support of the industry group members represented on
                                                                                                Standards Committee EL-049 in the preparation of this Handbook.

                                                                                                Reading this information will assist in selecting a safe meter for a particular application.
                                                                                                NOTES:
                                                                                                1. AS 61010.1 applies to electrical equipment that is used for testing, measuring, control and laboratory use on
                                                                                                   circuits operating at ‘low voltage’ as defined by AS/NZS 3000, Electrical installations. (i.e. for voltages not
                                                                                                   exceeding 1000 V a.c. or 1500 V d.c.).
                                                                                                2. This Handbook explains the measurement categories and voltage ratings as these are the primary design
                                                                                                   safety markings that users can identify on the outside of the meter and packaging.
                                                                                                3. To correctly specify a meter, both the measurement category and voltage must be stated. e.g. CAT III 600 V.
                                                                                                4. Whilst this Handbook has been written for users selecting a digital multimeter, the safety criteria are equally
                                                                                                   applicable to all test and measuring equipment.
                                                                                                5. AS 61010.1 is almost identical to IEC 61010-1 except for minor changes to Tests for resistance to fire. All
                                                                                                   imported equipment will refer to IEC 61010-1.
                                                                                                6. The photographs used in this Handbook as examples show particular brands of test and measuring equipment,
                                                                                                   however other brands would also be acceptable if they comply with AS 61010.1.
                                                                                                7. It is recommended that all personnel (including apprentices and trainees) who are required to use a voltage
                                                                                                   detecting device (such as a multimeter) to verify electrical isolations for their personal safety or the safety of
                                                                                                   other workers be given a copy of this Handbook. The contents of this Handbook should be included in electrical
                                                                                                   safety training at TAFE and in the workplace.
                                                                                                8.    It is recommended that all sales outlets offering this equipment for sale place a printed copy of this Handbook
                                                                                                     in public view next to the equipment so that customers may read it for themselves.

                                                                                                                                                     CAUTION
                                                                                                Personnel who sell test and measuring equipment may not be familiar with AS 61010.1 nor
                                                                                                understand what the Measurement Categories and Voltage Ratings mean. It is expected that
                                                                                                distributors of test and measuring equipment will provide copies of this Handbook for the
                                                                                                information of their sales staff. This will ensure the customer is provided with technically
                                                                                                accurate information so they can make an informed selection of test and measuring
                                                                                                equipment to suit their application.
                                                                                                                                                            3                                                     HB 187—2006




                                                                                                                                                   CONTENTS

                                                                                                                                                                                                                         Page

                                                                                           1    BASIC INFORMATION ..................................................................................................... 4
                                                                                                1.1 Information needed prior to purchase ...................................................................... 5
                                                                                                1.2 Product safety and independent testing .................................................................. 5
                                                                                                1.3 Selecting a safe multimeter ..................................................................................... 5
                                                                                           2    FURTHER INFORMATION ............................................................................................... 6
                                                                                              2.1       Safety requirements ................................................................................................ 6
                                                                                              2.2       Hazards when using multimeters............................................................................. 7
                                                                                              2.3       Selecting the measurement category .................................................................... 10
                                                                                              2.4       Selecting the voltage rating................................................................................... 12
                                                                                              2.5       Markings on the meter .......................................................................................... 13
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                                                                                              2.6       Need for independent testing ................................................................................ 13
                                                                                              2.7       What does the CE symbol indicate? ...................................................................... 14
                                                                                              2.8       Product safety for test leads and accessories ....................................................... 14
                                                                                              2.9       Safe testing practice ............................................................................................. 14
                                                                                              2.10      Good design features............................................................................................ 15
                                                                                              2.11      Operating instructions ........................................................................................... 16
                                                                                              2.12      Other types of equipment ...................................................................................... 18
                                                                                              2.13      Fault currents........................................................................................................ 19
                                                                                              2.14      Installation overvoltage and measurement categories ........................................... 20
                                                                                              2.15      Voltage ratings...................................................................................................... 20
                                                                                              2.16      Transient voltage spikes ....................................................................................... 21
                                                                                              2.17      Transient voltage protection .................................................................................. 22
                                                                                              2.18      Input protection ..................................................................................................... 22
                                                                                              2.19      Minimum fault rating of multimeter fuse................................................................. 23
                                                                                           Annex A     Contact information ................................................................................................ 24
                                                                                           Annex B Effects of electricity on the human body ................................................................. 25
                                                                                           Annex C Working safely ....................................................................................................... 26
                                                                                           HB 187—2006                                            4


                                                                                                                                   STANDARDS AUSTRALIA


                                                                                                                                      Australian handbook

                                                                                                                             Guide to selecting a safe multimeter


                                                                                                 1    BASIC INFORMATION

                                                                                                 Multimeters are widely used to measure electrical parameters such as voltages, currents,
                                                                                                 resistance in a.c and d.c circuits. The electrical circuits to which we connect our multimeters
                                                                                                 when testing or measuring do not have a perfectly smooth voltage waveform. When electrical
                                                                                                 equipment which is connected to the power distribution system is switched on or off or
                                                                                                 lightning strikes the overhead power lines, very high voltage spikes of several thousand volts
                                                                                                 can be transmitted along the power lines. Whilst the voltage spikes may only last for several
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                                                                                                 microseconds, they cause damage by breakdown of the insulation in the equipment and allow
                                                                                                 very high fault currents to flow.

                                                                                                 These high voltage spikes can create a serious hazard for the person using the multimeter. If
                                                                                                 the person is taking measurements on electrical systems, voltage spikes are almost invisible
                                                                                                 and largely unavoidable. They occur randomly and can attain peak values in the many
                                                                                                 thousands of volts.

                                                                                                 One has to depend on the protective circuits built into the meter for protection, i.e. the high
                                                                                                 rupturing capacity fuses and voltage dependent resistors. The voltage rating alone is not an
                                                                                                 indication as to how well a meter is designed to protect against these transient voltage spikes.

                                                                                                 For example, if you were to measure the voltage at a 240 V power outlet, the display may
                                                                                                 show—




                                                                                                 But the meter may actually be seeing this:



                                                                                                                                               8000 V
                                                                                                                                               s p ikes



                                                                                                                                                      24 0 V AC R M S
                                                                                                                                                      s i n ewave




                                                                                                                   Figure 1: A typical 240 V a.c. 50 Hz waveform showing randomly
                                                                                                                                    generated high voltage spikes




                                                                                           © Standards Australia                                                                    www.standards.org.au
                                                                                                                                                            5                                               HB 187—2006

                                                                                                 Early clues about the safety hazard posed by transient voltage spikes came from applications
                                                                                                 involving measurements on the power supply of electric commuter trams. The nominal voltage
                                                                                                 was only 600 V, but multimeters rated at 1000 V lasted only a few minutes when taking
                                                                                                 measurements while the tram was operating. Investigations revealed that the tram stopping
                                                                                                 and starting generated spikes of 10 000 V magnitude. These destroyed early multimeter input
                                                                                                 circuits. The lessons learned through this investigation led to significant improvements in
                                                                                                 multimeter input protection circuits.

                                                                                                 1.1     Information needed prior to purchase

                                                                                                 1.1.1     What is the highest category of electrical circuits you intend to measure?

                                                                                                 Categories indicate the amount of energy available in the circuit. The higher the circuit
                                                                                                 energy, the higher the category required. The higher the category, the safer the meter.

                                                                                                  CAT I—very low energy                e.g. Vehicles, battery-powered circuits (not connected to
                                                                                                       circuits                              240 V)
                                                                                                  CAT II—low energy                    e.g. Domestic use (up to 5 kA fault currents)
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                                                                                                       circuits
                                                                                                  CAT III—medium energy                e.g. Industrial + commercial use (up to 25 kA fault currents)
                                                                                                       circuits
                                                                                                  CAT IV—high energy                   e.g. Industrial + commercial use (above 25 kA fault currents)
                                                                                                       circuits
                                                                                                 1.1.2     What is the highest voltage of electrical circuits you intend to measure?

                                                                                                 Standard voltages specified in AS 61010.1 are 50, 100, 150, 300, 600 and 1000. For
                                                                                                 multimeters offered for sale in Australia where the standard distribution voltages are
                                                                                                 240 V a.c. (phase to neutral) and 415 V a.c. (phase to phase), generally 300 V, 600 V or
                                                                                                 1000 V meters will suffice. Industry can have equipment that could generate up to 1000 V a.c.
                                                                                                 or d.c.
                                                                                                 Note: See AS 60038 for details on standard voltages. Also see Clause 2.4 of this Handbook.

                                                                                                 1.1.3     Do you need to measure other electrical parameters?

                                                                                                 Most multimeters provide measurement of a.c. volts, d.c. volts, a.c. amps, d.c. amps and
                                                                                                 resistance. Some multimeters provide additional measurement functions such as capacitance,
                                                                                                 frequency, diode test, temperature, etc.

                                                                                                 1.2     Product safety and independent testing

                                                                                                 Whilst the designers have sought to design a safe product, until the product is manufactured,
                                                                                                 assembled and tested it is not possible to verify that the outcome of the combined process
                                                                                                 (design, manufacturing and assembly) has produced a safe product. There is always a risk
                                                                                                 that the design may be flawed, or that the materials used may not be suitable or that there are
                                                                                                 other factors, which may jeopardize the safety of the product.

                                                                                                 The only means of verifying compliance with the safety standard AS 61010.1 is to look for the
                                                                                                 accredited testing laboratory certification mark (UL, CSA, VDE, TUV, TCA) moulded into or
                                                                                                 printed on the back of the product and on any accessories such as test leads.

                                                                                                 1.3     Selecting a safe multimeter

                                                                                                 Step 1:      Ask the sales staff to show you multimeters with the category and voltage
                                                                                                              information you require.

                                                                                                 Step 2:      Inspect each multimeter closely (take it out of the box if necessary). Look for the
                                                                                                              category and voltage marking on the front adjacent to the terminals and for the
                                                                                                              accredited testing laboratory certification mark at the rear of the instrument.
                                                                                                              NOTE - ‘CE’ is not a test laboratory certification mark and is not relevant in Australia.


                                                                                           www.standards.org.au                                                                                           © Standards Australia
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                                                                                                             HB 187-2006, Guide to selecting a safe multimeter
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