1 Scope

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.

Summary of Topics

These revisions to UL 991 are being issued to address editorial maintenance of UL Standards for Safety. These revisions are considered to be non-substantive and not subject to UL's STP process.