Cal Test Electronics CT3900B UL Listed DMM Probes and Accessories comply with UL 61010-031 (2nd Edition) safety standards and feature the UL logo. Core members of the Cal Test Electronics CT3900B series are handheld probes featuring an ergonomic nose and locking safety cap. The cap, when in-place, limits tip exposure to a 4mm maximum. This small exposure limits arc-flash while probing into high-energy environments, such as CAT III and CAT IV. The probes, with safety caps in place, are rated to 1000V CAT III / 600V CAT IV.