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For Phil Corso or anyone with specific information, There are still some PWM drives on the market without intelligent programmable/adjustable motor protection features. For these apps, in-line fuses are still typically used in cases where the motor rating is less than the drive rating. Example: drive protection 10Arms (not adjustable) and 5Arms motor. We recently had a customer with an unusual motion control application in that the machine can frequently jam. Because they desired to try and fight through potential hard jams, the following error was set very loose and a jam could occur such that the fuses were the only motor protection. The glass type 250Vac fuses did their job but would sometimes blow violently and a few times even started an electrical fire. They tried ceramic sand filled fuses and these could also blow in pieces although (per fuse mfg) the sand filling acts as an arc extinguisher and fires are much less likely. Finally, the fuse mfg agreed with my original hunch that fuses designed for 60Hz or pure DC waveforms may not be suitable for PWM waveforms where instead of 60 peaks per second (60Hz) you get 4,000 - 20,000 peaks per second of Vac X 1.4 with very high dV/dt and possibly some spiking. The fuse mfg advised switching to 600Vac class electrical power fuses versus the 250Vac class electronic fuses. We assume the customer installed the 600V fuses as we haven't heard back since (about 3 weeks). 1. Has anyone else had the same experience [or info] re. fuse voltage rating for PWM drive? When I talk to fuse app engineers about PWM waveforms they act as if I've invented some new kind of waveform etc. 2. Has anyone ever heard of fusing only two of the three motor phases? I'm trying to convince an engineer that this is a no-no. I gave him all the reasons why. We found the NEC rule that says all "un-grounded" conductors must be current protected etc. Thanks, Tom Gianni