Electric Shock Hazards: Accessible parts over 30Vrms

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Fundamentals of Product Safety DesignBerri
RemenickNARTE Certified Product Safety
EngineerProduct Safety ManagerWashington
Laboratories, Ltd.September 14,
2007Gaithersburg, MD
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Outline

• Background
• Insulation
• Component Selection
• Labeling
• Documentation
• Wiring
• Resistance to Fire

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Product Safety Requirements

• US/Canada
• NRTL Listing (cULus, cTUVus, cCSAus)
• Legal requirement, customer requirement, or to
  limit liability
• Europe
• CE Mark
• Legal requirement
• Others
• CB Report
• To facilitate International Approvals.

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Product Safety Hazards

• Electric Shock Hazards Accessible parts over
  30Vrms, 42.4Pk, or 60VDC.
• Energy Hazards Energy level over 240VA or 8A
• Fire Hazards Materials, Enclosure, Abnormal
  conditions
• Mechanical Hazards Moving parts, Sharp edges,
  Tipping, Handles
• Radiation Hazards Lasers, UV, Sonic
• Thermal Hazards External temps, component temps

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Product Safety Design Guidelines
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Design Requirements

• Protection against electric shock and energy
  hazards
• The OPERATOR can not touch bare or inadequately
  insulated parts at hazardous voltage or energy
  levels.
• Hazardous Voltage Level is typically gt30Vrms,
  42.4Vpeak, or 60VDC.
• Hazardous energy is typically gt240VA or 8A
• Protection may be provided via insulation,
  guarding or interlocking.

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What is Insulation?

• Physical barrier between two parts (tape, plastic
  shield, wire insulation, enclosure, etc)
• Separation between two parts through air or along
  a surface (creepage or clearance distance)

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Insulation Types

• Functional / Operational Insulation (DC input to
  ground)
• Basic Insulation (Primary to Ground, TNV to
  Ground, TNV to SELV)
• Reinforced Insulation (Primary to Secondary)

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Reinforced Insulation Example
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Spacings (Creepage / Clearance)

• Based on the required insulation for your
  circuit.
• Based on the maximum working voltage for your
  circuit.
• Based on the environment the product will be used
  in (Pollution Degree)
• Based on the PCB material Material Group -
  Comparitive Tracking Index (CTI)

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Creepage / Clearance
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Creepage / Clearance

• Creepage
• Creepage distance between two points along the
  surface
• Creepage is measured on 11 artwork or on a blank
  board
• Locations of circuits determined by reviewing
  schematics
• Clearance
• Clearance distance between two points through
  the air
• Clearance is measured on a populated sample

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Component Selection

• Safety Critical Components must have the
  appropriate approvals or additional evaluation
  will be required.
• Safety Critical Components
• Devices in the AC path (inlets, fuses, switches,
  power supplies, transformers, etc.)
• Motors, fans
• Power conversion components (AC-DC or DC-DC
  Converters)
• Any isolation component (Transformer, Bridging
  Capacitors, MOVs,)
• Wiring
• Batteries
• Others depending on their application.

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Component Selection

• For NRTL approvals, all components must be UL
  approved.
• For CE Mark approvals, all components must have a
  European approval such as CE, TUV, VDE, etc.
  (exception fuses and wiring can be UL approved)
• For GS or CB Scheme approvals, all components
  must have a TUV, VDE, or other official European
  approval. CE Mark is not acceptable for these
  approvals.
• Approval certificates required (TUV or VDE Cert,
  CE Declaration of Conformity, UL File number,
  etc.)

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Labeling and Marking

• Rated voltage, current or power, frequency
• Manufacturers name or registered trademark.
• Model or type number.
• Fuse replacement info (if applicable).
• IEC symbols wherever possible.
• Warnings and Cautions appropriate for the
  particular equipment.

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User Instructions

• Installation Instructions - information regarding
  mounting, connection to the supply, ventilation,
  input ratings, etc.
• All information regarding use, cleaning,
  maintenance (if necessary).
• All safety warnings and cautions.
• Rack Mount instructions.
• Safety-related information to be in appropriate
  language of the country you are exporting to.
• Some standards have entire sections of specific
  info that must be in manual.

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Wiring and connection to the supply Protective
Earth -

• PE conductor must be green/yellow or bare
  insulation conductor
• PE connections must be double secured so that
  both the wire and insulation are crimped
• IEC PE symbol shall be marked adjacent to PE stud
• PE conductor shall connect to chassis directly
  from input (inlet, terminal block, etc).
• PE conductor must be secured with washer and
  locknut.
• Additional PE conductors can be secured to PE
  stud with a second washer and locknut.

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PE Stud Example
EMI FILTER
CHASSIS
TO OTHER
CONNECTION
GROUNDS
MECHANICALLY SECURED
GROUND GREEN/YELLOW WIRE
SAME GAUGE AS OR BIGGER THAN SUPPLY
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Wiring and connection to the supply Primary
Wiring -

• All AC wires shall be double secured. Double
  securement can be met by
• Double crimp connector or
• Single crimp connector and cable tie or
• Single crimp connector and shrink sleeving.
  
• AC wiring shall be rated for the maximum working
  voltage and current.
• AC wiring shall be isolated from low voltage
  wiring or low voltage parts, this can be
  accomplished by
• Shrink sleeving the AC conductors or
• By routing the AC conductors away from low
  voltage wires
• and securing with cable ties or
• By using UL1015 Reinforced Insulation wire.

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Resistance to fire and control of fire spreading

• Enclosures, components, and other parts shall be
  constructed such that propagation of fire is
  limited. Flammability of enclosure, internal,
  and external parts shall be adequate for the use
  of that part.
• Flammability ratings
• 5VA Most fire resistant
• 5VB
• V0
• V1
• V2
• HB40
• HB75 - Least fire resistant
• Foamed materials
• HF-1
• HF-2
• HBF

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Resistance to fire and control of spread of fire

• 60950-1
• Fire enclosure openings shall be
• Top and side openings shall be
• less than 5mm in any dimension or
• less than 1mm in width regardless of length
  or
• meet the 5? projection rule.
• There shall be no bottom openings (some
  exceptions allowed but difficult to meet)
  

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Methods for Meeting Fire Requirements in 61010-1

• Requirement There shall be no spread of fire
  outside the equipment in Normal or Single Fault
  Conditions.
• Methods of Compliance
• A Testing in single fault conditions
• B Reducing sources of ignition within the
  equipment
• C Containing fire within the equipment should
  it occur

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Requirements for fire enclosure

• - Components in primary circuit
• - Components in secondary circuits that are not
  
• supplied by LPS
• - Components in secondary circuits supplied by
  LPS
• but not on V-1 material
• - Components with unenclosed arcing parts
• - Insulated wiring

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Parts not requiring Fire Enclosure

• - Motors
• - Transformers
• - Wiring and cabling insulated with PVC, TFE,
  PTFE,
• FEP, neoprene or polymide
• - Connectors in secondary circuits powered by
  less
• than 15VA or LPS
• - Components in secondary circuits supplied by
  LPS
• and on V-1 material
• - Components in secondary circuits supply by
  max
• 15VA and on HB785 if lt3mm or HB40 if gt3mm.

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Plastic materials used for fire enclosure

• Movable equipment lt18kg
• V-1 or pass A.2
• HWI test (if lt13mm from high temp parts)
• Movable equipment gt18kg or stationary equipment
  
• 5VB or pass A.1
• HWI test (if lt13mm from high temp parts)
• Materials filling an opening in a fire enclosure
  
• V-1 or pass A.2

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Plastic materials used inside a fire enclosure

• Inside a fire enclosure
• V-2 or HF-2 or pass A.2
• Exceptions
• Electronic components (ICs, optos, etc.) mounted
  on V-1.
• Wiring and connectors insulated with PVC, TFE,
  PTFE, FEP, neoprene, or polymide.
• Clamps, cable ties.
• Wire marked VW-1 or FT-1 or better.
• Others.

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Plastic materials used outside a fire enclosure

• Material outside fire enclosure
• HB75 if lt3mm or HB40 if gt3mm or HBF or Glow Wire
  test at 550C
• Connectors
• V-2 or pass A.2 or mounted on V-1 and be small or
  be in secondary circuit with max 15VA
• Exceptions
• Electronic components (ICs, optos, etc.) mounted
  on V-1.
• Wiring and connectors insulated with PVC, TFE,
  PTFE, FEP, neoprene, or polymide.
• Clamps, cable ties.
• Others.

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Washington Laboratories, Ltd.

• Help you select the proper Directives and
  Standards to apply to your product.
• Evaluate and test your product to the appropriate
  Safety Standard and offer solutions for
  non-compliances.
• Provide product design assistance.
• Obtain cTUVus, cCSAus, cULus, GS Mark, and other
  approvals.
• WLL is a Partner Test Lab for TUV Rheinland for
  60950-1, 61010-1, and 60065

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Washington Laboratories, Ltd.

• Give us a call or send us info about your product
  - were here to help!
• Berri Remenick
• Product Safety Manager
• Phone [phone]
• Fax [phone]
• E-mail berrir_at_wll.com