I've been reading up on VFDs for the PM-935TS. I think I've settled on the Automation Direct GS21-23P0. If I'm reading the manual correctly, it calls for a 50A fuse and 70A breaker. That seems quite a bit higher than the similarly sized Hitachi. For anyone with this VFD, what circuit protection did you use? If lower than the manual recommendation, have you had any nuisance tripping?
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GS21-23P0 VFD fuse/cb for PM-935TS
- Thread starter jtf314
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Fusing is based on the use of fast blow type which are typically 2X higher than dual element types. Although fast blow fuses are recommended for semiconductors, there is quite a bit of discussions as to the pros and cons of their use with VFDs. In the lower price range VFD's (i.e. those that do not have modular replaceable components) they are not worth the cost of repairing and there is little benefit to using fast blow types. On this size VFD I typically use Bussman Low-Peak CC 30A fuses and never have had an issue with using that size/type of fuse. I also usually recommend a minimum of a 30A breaker for 3 Hp on single phase 230VAC. The fusses and CC fuse holders are inexpensive, I often pick them up on eBay as NOS, not used. The low peak track very closely to current curves that might be encountered with a VFD, I have yet to see one let go unless there was a drive failure.
Fuse: Bussmann LP-CC-30 Class CC Low-Peak Time Delay Fuse (Buy from US vendors where you can see the actual fuse/box, most of those from Asian are reproductions)
Fuse Holder: Allen Bradley 1492-FB2C30-L Fuse Holder 30 Amp 600 Volt 2 Pole for Class CC Fuse
FYI, most of the discussion of the use of fast acting fuses did no better for protecting drives vs. standard fuses according to others that are in the field. Part of this may also be that although the fuse limits the input current, there is a lot of stored energy within the capacitor banks, so when that energy is released because of a component failure/short it still is going to do a lot of damage. The only failures that I have seen in mainstream types has been a failure of the inrush protection circuitry most likely because of two frequent power cycling and not letting the capacitors discharge before energizing the VFD. I have yet to see a VFD fail in the past 15 years with lots of installs, but have seen/replaced quite a few HY, Lapond and similar inexpensive VFDs. The last HY that died was on a lathe, was replaced with a GS21 VFD and it performed much better.
Fuse: Bussmann LP-CC-30 Class CC Low-Peak Time Delay Fuse (Buy from US vendors where you can see the actual fuse/box, most of those from Asian are reproductions)
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Fuse Holder: Allen Bradley 1492-FB2C30-L Fuse Holder 30 Amp 600 Volt 2 Pole for Class CC Fuse
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FYI, most of the discussion of the use of fast acting fuses did no better for protecting drives vs. standard fuses according to others that are in the field. Part of this may also be that although the fuse limits the input current, there is a lot of stored energy within the capacitor banks, so when that energy is released because of a component failure/short it still is going to do a lot of damage. The only failures that I have seen in mainstream types has been a failure of the inrush protection circuitry most likely because of two frequent power cycling and not letting the capacitors discharge before energizing the VFD. I have yet to see a VFD fail in the past 15 years with lots of installs, but have seen/replaced quite a few HY, Lapond and similar inexpensive VFDs. The last HY that died was on a lathe, was replaced with a GS21 VFD and it performed much better.
Excellent info! I’ll look into those fuses and holders and probably go with a 40A breaker. I’ve come across quite a few of your posts in my research. Thanks for sharing your knowledge and experience with these VFD setups over the years.
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Mark is right, no matter what you put in the line (breaker or fuse) if the unit fails internally nothing will protect it- only the house wiring will be protected
Makes sense. Yeah, I’m not so worried about protecting the VFD anyways since, as Mark says, they’re not worth repairing. I was mainly concerned with a lower rated fuse/cb nuisance tripping which it sounds like I don’t need to worry about.
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Nope, you're good.