UL 991

Standard for Tests for Safety-Related Controls Employing Solid-State Devices

1.1 These requirements apply to controls that employ solid-state devices and are intended for specified safety-related protective functions.

1.2 These requirements address the potential risks unique to the electronic nature of a control. Equipment or components employing an electronic feature shall also comply with the basic construction and performance requirements contained in the applicable end-product or component standard. These requirements are intended to supplement applicable end-product or component standards and are not intended to serve as the sole basis for investigating the risks of fire, electric shock, or injury to persons associated with a control.

1.3 These requirements do not cover controls covered by end-product standards in which an electronic control investigation is specified.

1.4 Sections 9 - 22 contain standardized test methods for investigating the performance of an electronic control when subjected to particular environmental stresses. The suitability of each test to a given control shall be determined by the end-product standard(s). Determination shall include an assessment of:

a)    Whether the control will be exposed to a particular environmental stress in its application, and

b)    Whether the response of the control to a particular environmental stress is relevant to its intended safety-related protective function in its application.


  • Edition Number: 3
  • Edition Date: 10/22/2004
  • Price Code: A
  • Type: ulstd
  • ANSI Approved:
  • DOD Approved: