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: Alastair.McLaughlin@TUV-SUD.co.uk
• Phone: +44 (0)1789 731155
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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
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Basic Safety Principles
Why safety?
What hazards to consider
Basic Safety Principles
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
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Basic Safety Principles
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:
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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
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Basic Safety Principles
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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
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Basic Safety Principles
Electric shock
• Electric shock is due to current passing through the body
• It can cause:
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Perception
Reaction
Inability to let go
Ventricular fibrillation
Cell damage
Burn hazard (high frequency)
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< 0.5mA
0.5 - 5mA
5 - 10mA
20 - 30mA
> 30mA
> 30mA
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Basic Safety Principles
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
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Basic Safety Principles
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)
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Basic Safety Principles
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
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Operator access areas
Service access areas
Restricted access locations (RAL)
Permanently connected equipment
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Basic Safety Principles
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
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Basic Safety Principles
Fire hazard
Fires may be caused by high temperatures resulting from:
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Overloads
Component failures
Insulation breakdown
High contact resistance
Loose connections
Foreign bodies
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Basic Safety Principles
Fire hazard
• Approach to limiting risk of propagation:
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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
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Basic Safety Principles
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
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Basic Safety Principles
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
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Basic Safety Principles
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
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Basic Safety Principles
Radiation Hazard
Equipment operators and service personnel shall be protected from injurious levels
of radiation emissions
• Types of radiation include:
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Laser (light) radiation IEC 60825-1
X-ray (e.g. CRTs)
Radio frequency
Ultraviolet (UV) light
• Provide barriers to radiation
• Limit radiation levels
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Basic Safety Principles
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:
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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
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Basic Safety Principles
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
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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
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Submitting for Testing
• Regulations, directives and laws tell us products must be safe
• Technical standards give the means to prove safety
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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)
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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:
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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:
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Market access
Consumer confidence
Ongoing production quality
Marketing advantage
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Submitting for Safety Testing
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
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Submitting for Safety Testing
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
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Submitting for Safety Testing
• Requesting a Quotation
– Know your market
 Different test requirements for different markets
– Provide as much information as possible
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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
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Submitting for Safety Testing
• Collate documentation before submitting
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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
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Worst case normal load conditions
Prepare support equipment loads & cabling
Provide clear operating instructions
Write test software
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Submitting for Safety Testing
• Find out how many samples are required
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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
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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
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Submitting for Safety Testing
Safety Critical Components & Materials
• Which Components are Safety Critical?
– Mains components:
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Mains plugs and cords
Appliance couplers
Fuse and fuseholders
Wiring
Power supplies
X and Y-capacitors
Transformers
– Other components:
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DC-DC converters
Fans
Enclosure materials
Connectors
PCB material
Thermistors and PTCs
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Submitting for Safety Testing
Safety Critical Components & Materials
• 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
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Submitting for Safety Testing
Safety Critical Components & Materials
• 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
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Submitting for Safety Testing
Safety Critical Components & Materials
• 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:
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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
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Submitting for Safety Testing
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
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Submitting for Safety Testing
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
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Submitting for Safety Testing
• UL Power Supply Listing
Ratings
Model number
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Submitting for Safety Testing
• Example of VDE listing
Model number
Ratings
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Submitting for Safety Testing
• CB Certificates
– Test report forms part of certificate
Ratings
Model number
Test standard
Number of pages
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Submitting for Safety Testing
• NRTL Certificates
Ratings
Model number
Test standard
Number of pages
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Submitting for Safety Testing
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
• CSA
– x
– 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
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Submitting for Safety Testing
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
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Summary
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
Thanks for listening!
Any questions?
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