TMC8 Thermomagnetic Circuit Breakers Phoenix Contact TMC8 Series Thermomagnetic Circuit Breakers are UL Listed 489 breakers and feature a trip-free design that opens during an overcurrent event, even if the switch is held closed. The TMC8 series also offers a snap-action mechanism that creates a longer-lasting product by eliminating contact welding and reducing contact wear and pitting. These breakers come in 1-, 2-, and 3-pole options, and each one also comes in B-, C-, and D-curve options to ensure the proper trip speed based on user end devices. A vast array of accessories are available to further increase a system’s functionality including an auxiliary contact, alarm contact, and shunt trip. TMC8 breakers can also be bussed together utilizing a cuttable UL Listed busbar.