UL 1004-3:2018 pdf download.Thermally Protected Motors.
4.2 Because a solid-state relay is considered a potential single-point of failure (i.e., the relay "contacts"may fail in the shorted condition thus obviating the protective functionality), solid-state relays may only beused in this capacity if either redundancy is provided or the solid-state relay complies with the Standardfor Automatic Electrical Controls for Household and Similar Use，Part 1: General Requirements,UL60730-1.
5 lntentionally Weak Trace (IwT)
5.1 A motor, as described in 7.10, shall comply with the requirements of this Section and Section 11,lntentionally Weak Trace (IwT) Tests
5.2 IWTs shall:
a)Not be used in lieu of branch circuit overcurrent protection;b) Be designed as single use; and
c) Not be designed or considered to be a user-serviceable part.
5.3 lf the lWT opens, the printed-wiring board (PWB) or the entire control shall be replaced or discarded.Bridging of an opened WT with a fuse or other overcurrent protective device shall not be permitted.
5.4 lt shall be established whether reliable performance of the WT is required to provide a required safetyfunction,i.e.，motor overtemperature protection,11.2.
5.5 lt shall be established whether the WT is designed as a full range device,11.4, or is intended toprotect against catastrophic,short-circuit,conditions only.
5.6 lf the lWT is determined to be designed to function as a full range device, the rating of the IWT shallbe established in accordance with 11.3.
