What Is UL 1685?

UL 1685, formally titled the Vertical-Tray Fire-Propagation and Smoke-Release Test for Electrical and Optical-Fiber Cables, is a flammability standard used to evaluate the fire performance of cables installed in vertical trays. This test measures both flame spread and, in certain protocols, smoke release, under conditions intended to simulate cable installations in industrial and commercial settings.

In the UL flame exposure method, a 24-foot vertical cable tray is loaded with the test cable, and a 70,000 BTU/hr ribbon burner is applied to the bottom of the tray for 20 minutes. The primary acceptance criterion is that the charred portion of the cable must not extend more than 8 feet above the burner. In the optional NFPA 262/UL 1685 smoke test variant, the total smoke release is also measured, and the peak smoke release rate must be 95 m² or less to pass.

A cable meeting UL 1685 requirements demonstrates strong resistance to vertical flame propagation, reducing the likelihood of fire traveling along cable pathways. This makes the standard particularly important for industrial, utility, and commercial facilities where vertical tray installations are common. UL 1685 compliance is often specified alongside other flame ratings—such as CSA FT4 or IEEE 1202 —depending on the governing codes and installation environment.