A Breaker is an electrical switch designed to protect an electrical circuit form damage caused by overload or short circuit. It automatically interrupts the power circuit in case of failures. Once the problem has been resolved, a Breaker can be reset to resume normal operation. Breakers come in a wide variety of sizes and specifications, depending on the circuit that they need to protect.
In wholesale colocation, the customer is often required to purchase and install its own breakers since the colocation vendor will typically not know the individual circuits required to each server rack.