designing for safety - tuv sud · designing for safety ... –iec webstore gives latest editions...

Designing For Safety

A short guide to safety in electrical and

electronic products

Who am I?

• Alastair McLaughlin

• Product Safety Specialist at TÜV SÜD Product Service

• Over 20 years experience in compliance management and product testing – Worked for retail suppliers, major children’s product manufacturers, and TÜV SÜD

Product Service

• Email: [email protected]

• Phone: +44 (0)1789 731155

TÜV SÜD Product Service Slide 2

mailto:[email protected]



Contents

• Basic Safety Principles

– Why safety?

– What hazards to consider

• Submitting for Safety Testing

– Selection of test standards

– Hints and tips to minimise failures

• Questions and answers


Basic Safety Principles

Why safety?

What hazards to consider


Why safety?

We have a duty of care to our end-users to ensure products are safe

• Legislation lays out safety requirements in broad terms – Low Voltage Directive

(including as required by R&TTE)

– General Product Safety Directive



EU law (the Low Voltage Directive) requires that products:

• be made in such a way as to ensure that it can be safely and properly assembled and connected

• protect against hazards arising from the electrical equipment to ensure: – that persons and domestic animals are adequately protected against the danger of physical

injury or other harm which might be caused by direct or indirect contact

– that temperatures, arcs or radiation which would cause a danger, are not produced

– that the insulation must be suitable for foreseeable conditions

• protect against hazards which may be caused by external influences on the electrical equipment to ensure: – that the electrical equipment meets the expected mechanical requirements in such a way

that persons, domestic animals and property are not endangered

– that the electrical equipment shall be resistant to non-mechanical influences in expected environmental conditions, in such a way that persons, domestic animals and property are not endangered

– that the electrical equipment shall not endanger persons, domestic animals and property in foreseeable conditions of overload



• Electric Shock

• Energy Hazards

• Fire

• Heat Hazards

• Mechanical Hazards

• Radiation

• Chemical Hazards

• Foreseeable Conditions – all the above hazards must be avoided in normal conditions…

– AND avoided under fault conditions



Electric shock

• Electric shock is due to current passing through the body

• It can cause: – Perception < 0.5mA

– Reaction 0.5 - 5mA

– Inability to let go 5 - 10mA

– Ventricular fibrillation 20 - 30mA

– Cell damage > 30mA

– Burn hazard (high frequency) > 30mA



Electric shock

• Direct contact with parts at hazardous voltage: – Secure covers to prevent access

• Breakdown of insulation between parts at hazardous voltage and accessible

conductive parts: – Double or reinforced insulation

– Earthed accessible conductive parts

• Leakage Current: – Limit leakage current to a safe value

– Select the lowest practical EMC filtering capacitors



Electric shock

• Law requires that insulation is suitable for foreseeable conditions

• Test standards require two levels of protection against electric shock – (i.e. equipment shall be safe under both normal AND single fault conditions)



Electric shock

Differing risk for different equipment (or parts of equipment):

• Moveable Equipment: – higher risk:

supply cord rupture, broken earth conductor

• Handheld Equipment: – wear and tear is higher

• Operator access areas

• Service access areas

• Restricted access locations (RAL)

• Permanently connected equipment



Energy hazard

High levels of electrical energy present a risk of injury (burns) or fire (ejection of

molten or incandescent material)

• Short-circuiting releases the energy very quickly

• Can happen in low-voltage circuits

• Protection can be provided by: – limiting user accessibility

– providing interlocks

– and guarding against accidental service personnel contact



Fire hazard

Fires may be caused by high temperatures resulting from:

• Overloads

• Component failures

• Insulation breakdown

• High contact resistance

• Loose connections

• Foreign bodies



Fire hazard

• Approach to limiting risk of propagation:

– Providing over-current / over-temperature protection

– Avoiding high temperatures

– Positioning combustible materials away from potential ignition sources

– Limiting quantity of combustible materials

– Using materials with low flammability

– Using enclosures / barriers



Heat Hazard

High temperatures under normal operating conditions can result in:

• Burns due to contact with hot parts

• Degradation of insulation & safety critical components

• Ignition of flammable liquids



Heat Hazard

• To reduce heat related hazards: – Avoid high temperatures

Add cooling features – fans or heatsinks

– Avoid temperatures above ignition points of flammable liquids

– Warning markings

– Restrict accessibility



Mechanical Hazard

Injury due the physical and mechanical properties of the equipment

• equipment stability

• sharp edges and corners

• ejected parts

• moving parts

• Approaches to limiting mechanical risks include: – Restricting accessibility

Guards, interlocks

– Stability testing

– Rounding of sharp edges and corners

– Warning markings



Radiation Hazard

Equipment operators and service personnel shall be protected from injurious levels

of radiation emissions

• Types of radiation include: – Laser (light) radiation IEC 60825-1

– X-ray (e.g. CRTs)

– Radio frequency

– Ultraviolet (UV) light

• Provide barriers to radiation

• Limit radiation levels



Chemical Hazard

Injuries may be caused by contact with or inhalation of chemicals, their vapours and

fumes.

• Protection against chemical hazards can be provided by: – Avoiding the use of chemicals likely to cause injury

– Limiting contact and inhalation

– Avoiding conditions likely to cause leakage or vaporisation

– Regular exchange of air to prevent vapour build-up

– Warning labels and instructions regarding precautions



Selection of Materials and Components

Must be selected and arranged to perform over the expected life of the equipment

without creating any hazard

• Compatible – with other materials or chemicals used

• Reliable – construction and arrangement

– in normal operation and fault conditions

• Used within their specified ratings

• Approved – to relevant component safety standards


Submitting for Safety

Testing

Selection of standards

Hints and tips to minimise failures

Submitting for Testing

Selection of standards

• IEC electrical safety standards – EN standards for electrical safety are derived from IEC standard

– Similarly many UL standards are derived from IEC

– EN and UL standards include group and national differences

• Editions of the standard – Harmonised standards in the EU give a presumption of conformity

– European Commission’s Official Journal (OJ) lists the current harmonised standards

– IEC webstore gives latest editions and amendments of the IEC standards

• National differences – Many European Standards impose Special National Conditions (SNCs)

– SNCs are mandatory when the product is supplied in those nations


Submitting for Testing

• Regulations, directives and laws tell us products must be safe

• Technical standards give the means to prove safety

– IEC 60065 (AV equipment)

– IEC 60335 (household appliances)

– IEC 60950 (office and IT equipment)

– IEC 61010 (lab and control equipment)

etc (specialist standards for other safety requirements)


Submitting for Safety Testing

Types of Safety Testing There are two approaches to safety testing • Type testing:

– A one-off test on a sample of the product. – Does not guarantee future product quality

CE marking (for inclusion in technical file) CB Scheme (as basis for obtaining international acceptance & certification)

• Product certification:

– An ongoing partnership between manufacturer and certification body – Initial testing of product – Regular factory inspections where the product is made – Certification mark permitted on the product – Benefits of certification:

Market access Consumer confidence Ongoing production quality Marketing advantage



Preparing in Advance: Design Stage

• Ensure design engineers are aware of safety requirements

• Seek advice from 3rd parties

– Enlist a consultant

– Consider a 3rd party design review at an early stage of development Highlight any issues with the design

Avoid re-design at a later stage

Advice on component and material selection



Preparing in Advance: Design Stage

• Select pre-approved components and materials

– Reduce testing requirements

– Avoid potential failures

– Avoid having to change / re-source components

– Know your target markets UL and EN standards required for US and EU respectively



• Requesting a Quotation – Know your market

Different test requirements for different markets

– Provide as much information as possible

Product description / Brochures

Photos / drawings

Define power requirements

Specify other facilities required (water, drainage, compressed air etc.)

Fan speed control or air conditioning incorporated in the product

Timescales required

Budget constraints



• Collate documentation before submitting – Circuit diagrams & schematics – Parts listings – Mechanical & exploded drawings – Critical component approvals information – User and service manuals – Rating label drawings – List all accessories and parts required to be included with the product – Define product families – List all production facilities

• Ensure that the equipment is suitably configured for testing – Worst case normal load conditions – Prepare support equipment loads & cabling – Provide clear operating instructions – Write test software



• Find out how many samples are required – Complete product

– Power supplies

– Fuses, thermal cut-outs and other components

– Plastic parts

• On-site testing can often be the most efficient way of testing – 100% of our engineers attention

– All your support facilities available

– Issues can be resolved face to face

– Fix your problems and clear non-compliances in parallel with the testing



Safety Critical Components & Materials

• Which Components are Safety Critical?

– Mains components: Mains plugs and cords Appliance couplers Fuse and fuseholders Wiring Power supplies X and Y-capacitors Transformers

– Other components: DC-DC converters Fans Enclosure materials Connectors PCB material Thermistors and PTCs




• Component approvals – IEC and EN investigations – Current test certificate / report

Note - some certificates have expiry dates

– Relevant IEC / EN standard

– In English

– From a CB, CCA or LVD accredited test laboratory (e.g. TÜV SÜD Product Service, VDE)

– Must include all relevant information some certificates are made up of many pages, all should be supplied

– If the test certificate does not give all of the required details then a copy of the test

report may be required e.g.: power supply units – more detailed information is required

– i.e. maximum rated ambient, classification of outputs, method of mains isolation




• Self-declaration may also be accepted – A certificate of conformity (CofC), manufacturer’s declaration

– You remain responsible that the component is suitably approved

– This will be stated in any test report issued

• For a Third Party Certification, self-declaration is NOT acceptable – 3rd party approved components MUST be used

– (e.g. TÜV SÜD PS, UL, CB, VDE)

• Note: do not rely statements like “designed to meet” or “complies with ENxxxx” – These are NOT evidence of suitable component approvals




• Flammability of Materials – Plastic or non-metallic materials

– Compliance may be based on testing, and/or suitable documentary evidence

– Applicable standards: UL 94, IEC 60695

– To assess the suitability of the materials, the following information is required: Manufacturer name (eg: GE Plastics, 3M)

Name and part number of the material (e.g. Lexan, LX437)

Approval body’s file number (e.g. UL E12345)

Flammability rating (e.g. V-1, V-2, HB, HF2)

Thickness of material used



US / Canadian Investigations

• All safety critical components and materials must have current NRTL (Nationally

Recognized Test Laboratory) listing or recognition – The following information is required:

The name of the company that holds the NRTL approval

The type or model number of the component

The NRTL file number (e.g. UL E56789)

• Obtain a copy of the NRTL approval – From the approval holder, or the manufacturer of the component/part

– or from the NRTL’s website



US / Canadian Investigations

• Transformers with an insulation Class higher than Class A

– NRTL certification requires a NRTL Recognised insulation system (OBJY2) to be

employed.

– A recognised insulation system is a combination of materials that have been tested

together for suitability of use in prolonged high temperature conditions



• UL Power Supply Listing

Model number

Ratings



• Example of VDE listing

Model number

Ratings



• CB Certificates

– Test report forms part of certificate

Model number

Ratings

Test standard

Number of pages



• NRTL Certificates

Model number

Ratings

Test standard

Number of pages



On-Line Approvals Links • TÜV SÜD Product Service

– https://www.tuev-sued.de/industry_and_consumer_products/certificates – x

• ASTA and BEAB – http://www.astabeab.com/buyers.htm

– x

• CSA – http://directories.csa-international.org/

– x

• ENEC – http://www.enec.com/dev/recherche.php?soc=ENEC&s=2

– x

• Intertek – http://etlwhidirectory.etlsemko.com/WebClients/ITS/DLP/products.nsf/$$Search?OpenForm

– x

• ÖVE – http://www.ove.at/puz/reg/form.php

– x

• UL – http://database.ul.com/cgi-bin/XYV/template/LISEXT/1FRAME/index.htm

– X

• VDE – http://www.vde.de/VDE_PI_en/Zertifizierungsregister/detailSearch


https://www.tuev-sued.de/industry_and_consumer_products/certificates



http://www.enec.com/dev/recherche.php?soc=ENEC&s=2

http://www.astabeab.com/buyers.htm

http://directories.csa-international.org/



http://www.enec.com/dev/recherche.php?soc=ENEC&s=2

http://etlwhidirectory.etlsemko.com/WebClients/ITS/DLP/products.nsf/$$Search?OpenForm

http://www.ove.at/puz/reg/form.php

http://database.ul.com/cgi-bin/XYV/template/LISEXT/1FRAME/index.htm



http://www.vde.de/VDE_PI_en/Zertifizierungsregister/detailSearch


Hints and Tips

• Ensure support is available during testing – Select a nominated technical contact

• Attend on first day to assist with set up

• Respond to non-compliances as a package

• Advise when you are going to send new samples


Summary


Why safety?

What hazards to consider


Selection of test standards

Hints and tips to minimise failures

Questions and Answers

Thanks for listening!

Any questions?


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