A stepper motor may be wired in either series or parallel, depending on the needs of the application. A series-wired motor will deliver more stall torque, but torque drops quickly as velocity increases. A parallel-wired motor typically maintains its (lower-than-series) torque to a higher velocity.
Parallel wiring gives 1/4 the resistance and inductance of series wiring, resulting in more current, and therefore more heat generated. Therefore, we recommend that whenever you wire a motor in parallel, you limit its duty cycle to 50%, and engage Auto-Standby on the drive. This allows the motor to cool off between runs. The motor case temperature must always be kept below 100°C. If the motor is rising above 80°C, do something to prevent it from reaching 100C: attach a heat sink, lower the duty cycle, lower the current, etc. Heat sinks are usually the best way to effectively cool a motor.