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Understanding UL 508A Standards for Control Panels

Jul 31, 2024

UL 508A Standards for Industrial Control Panels

Introduction

  • Presenter: Chad Hitt, Application Engineer at Mechatronic Solutions
  • Overview of UL 508A standards for industrial control panels
  • Topics covered: Underwriter Laboratories (UL), definitions, differences between UL 508 and UL 508A, relationship with NEC, criteria for panel builds.

Underwriter Laboratories (UL)

  • Established for fire safety and electrical safety.
  • A global Safety Science organization that sets safety standards for various industries.
  • Transitioned from a nonprofit to a for-profit company in 2012.
  • Recognized by OSHA as a national testing laboratory.
  • UL Mark indicates a product has passed safety testing.

Definition of Industrial Control Panel

  • Industrial Control Panel: An assembly of two or more power and control circuit components for general industrial use at a voltage of 1,000 volts or less.
  • Components include:
    • Switches
    • Terminal blocks
    • Contactors
    • Motor drives
    • Transformers
  • Does not include motor control centers or switch gear.

Differences Between UL 508 and UL 508A

  • UL 508: Covers individual equipment and components (e.g., circuit breakers, power supplies).
  • UL 508A: Focuses on the assembly and installation of industrial control panels (enclosed and open).

UL Mark Significance

  • UL 508 Components: Indicates tested components that meet recognized standards.
  • UL 508A Control Panels: Assembled to UL508A standards with certified components.
  • Inspections by UL inspectors throughout the assembly process.
  • Requires a qualified Manufacturer Technical Representative (MTR) at panel-building facilities.

Relationship Between UL and NEC (National Electric Code)

  • NEC (NFPA 70) focuses on installation standards for electrical equipment.
  • UL standards relate to the construction and safety of the equipment.
  • Article 409 in NEC references UL 508A for industrial control panels.
  • NFPA 79 is the standard for electrical machinery beyond just control panels.

Is UL 508A Required?

  • Not mandatory by law but widely required by:
    • Electrical inspectors
    • Insurance providers
    • Equipment purchasers
  • Example: Minnesota statute requiring proof of compliance if the panel is not listed.

Criteria for Listing a Panel

  • Use of listed or recognized components.
  • Properly sized circuit protection (branch vs. supplementary).
  • Properly sized and marked wiring.
  • Adequate spacing for heat-producing devices.
  • Required markings and labels (name plates, warning labels, schematics).
  • Establishing a short circuit current rating (SCCR).

Listed vs. Recognized Components

  • Listed Components: Bear a UL mark indicating they are tested and certified.
  • Recognized Components: Tested for safety in specific applications; symbol is a backward UR.

Short Circuit Current Ratings (SCCR)

  • Defines the maximum current available during a short circuit.
  • Must be marked on equipment (e.g., breaker panels).
  • Both available fault current and SCCR must be calculated and documented.
  • SCCR must exceed available fault current to pass inspection.

Conclusion

  • UL 508A is a comprehensive standard with over 200 pages of guidelines.
  • Understanding UL 508A is critical for compliance and safety in industrial control panel installation.

Full transcript