Which UL standard states that fast response secondary protectors should be installed in a series?

The UL standard that outlines the requirement for fast response secondary protectors to be installed in a series is UL 1497. This standard specifically addresses surge protective devices and provides guidelines on their design, testing, and installation to ensure effective protection against transients caused by lightning or other sources. The series installation of these protectors is crucial because it allows for enhanced protection coordination and performance by ensuring that each protective device can work in tandem to clamp and absorb transient voltages effectively.

Additionally, UL 1497 details the operational characteristics and requirements that surge protective devices must meet, establishing reliability and safety in their application. Understanding this standard is essential for ensuring that the protective measures employed in outside plant design are compliant with industry safety and performance guidelines.