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Breaker and fuse sizing for VFD

sandiapaul

Titanium
Joined
Mar 19, 2004
Location
Princeton, NJ USA
Greetings,

I am wiring up a Teco 7300 VFD to a lathe.
Motor is 3HP. I have a separate on/off switch wired in before the VFD and after the main panel.

What size breaker should I put in my main panel and what fuse size should go in the on/off switch? I think 20 amp should be fine for the breaker, but what about the fuses in the switch?

I kind of backed myself into a corner with the switch as it takes the larger K size cartridge fuses(3"l) I did see that Bussman sells fuse adapters so you can use the smaller cartridge fuses.

Thanks for any help!
 
Look in the manual, it should call out the proper fuse or breaker.

Check page 3-5 for 7300CV. I assume the 003AC is your unit. If it is the 003BC, then the fuse sizes are smaller for 3 phase input.

https://elektromotor-online.nl/wp-content/uploads/2016/10/CV7300-Instruction-Manual-11-05.pdf

It shows fuses so the breaker is fairly irrelevant, and you use the fuse for protection. The breaker can be anything at or above the fuse rating, since the fuse will likely open first. It does suggest "current limiting" fuses "for best protection". That is a little odd, since I would have thought a UL recognition would have been with a specific fuse type.
 
Fuse cartridges of different sizes are not interchangeable, as there are different rating for different size fuses. Recommendations also varies somewhat by VFD manufacturer. Some give recommended fuse sizes, others state maximum size. Also some specify current limiting (fast acting) where others may specify dual element types. I have done a number of 3Hp single phase installations, I usually use a 30A J class or 30A CC fast acting (current limiting) fuse in these machine without problems. The breaker protects the wiring, so would be a minimum of 30A depending on the wire gauge used. Teco, Hitachi and fuse manufactures recommend use of fast acting fuse elements for VFDs of this size, Yaskawa if I recall specify a dual element (low-peak) fuses. You are also limited to the fuse size rating range by the holder.
 
Depending on your disconnect switch(heavy duty?) it may have an adjustable bottom block that can do different fuse lengths. Some general duty disconnects switches don't have that feature. I learned that recently...
 
Look in the manual, it should call out the proper fuse or breaker.

Check page 3-5 for 7300CV. I assume the 003AC is your unit. If it is the 003BC, then the fuse sizes are smaller for 3 phase input.

https://elektromotor-online.nl/wp-content/uploads/2016/10/CV7300-Instruction-Manual-11-05.pdf

It shows fuses so the breaker is fairly irrelevant, and you use the fuse for protection. The breaker can be anything at or above the fuse rating, since the fuse will likely open first. It does suggest "current limiting" fuses "for best protection". That is a little odd, since I would have thought a UL recognition would have been with a specific fuse type.
The one you linked to was from the Netherlands, so maybe it's not inclusive of UL info?

Here's what mine says:
"For UL type approval consider the following fuse types RK5, CC or T"

Also, you must use fuses, the only Circuit Breaker it is UL listed with is a Teco current limiting circuit breaker, and good luck finding one here. You can have any breaker AHEAD of the fuses, sized for whatever conductor size you want to run, but the UL listing of the VFD is only valid with one of those 3 types of fuses (the Chinese translation of "required" came out as "consider", I re-wrote that manual years ago for another brand-label of those Teco / Taian drives).
 








 
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