Siemens Thermal Magnetic Breakers provide three primary functions: 1) on-off switching, 2) over-current protection, and 3) short-circuit protection. The over-current protection is provided by a thermal trip element within the breaker. The short-circuit protection is provided by a magnetic trip element within the breaker. For easy review of the common types of thermal magnetic breakers, the products are divided into four categories: Type QP, Type QT, Type QD and Main Breakers.