The Q series of breakers all fit the I-line panels. These breakers are rated at 240 volts and are available in amperage from 70 to 225 amps. Many of the Q series breakers replace the old series. For example, the QD replaces the old KD style. Since both the old and new styles fit the I-line panels, the new style is a direct replacement.
Al the Q series breakers are available in a two- or three-pole configuration. Poles refers to the number of outputs for wires. Two-pole breakers have two lugs, and both wires are controlled by one common breaker inside a common case. Three-pole breakers have three lugs. All three wires are controlled by a common breaker inside a case.
The two-pole breakers have an internal ground that the electrician connects to the main building ground. In case of a short circuit inside the breaker itself, the electricity is diverted to ground instead of to the appliance the breaker is supposed to protect. This is an added optional feature included with the breakers.