Great question Anne, when sizing a motor filter first consider the length of motor lead between the motor and drive. If less than 50′ you may not need 1, if more than 50′ you might get away without 1 but should be verified by a qualified technician to see how high the spikes are at the motor junction box. Also makes a significant difference if using an “Inverter Duty” motor or not. Typically Inverter duty will have insulation class F rating good for higher temps and 2000volt peak tolerance. Standard insulation class B motors may only have a 1200volt peak rating. Then there is the Frequency ratings, 60Hz max speed and a Carrier Frequency setting in the drive of 2KHz to 4KHz are what these devices are rated for, ok?
Well if you need a special application accommodated and the motor and drive can’t be located less than 50′ apart, we can always consult the mfg for additional solutions. Besides sometimes you can get over 50′ out without a filter, especially if using an Inverter Duty motor, ok?