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Patriot

VFD Fusing - Mitsubishi FR-F740-00380-NA

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I am designing a system that will use the Mitsubishi FR-F740-00380-NA drive. I will be using 480V, 3 phase to power the drive for control of a 20 HP motor. As I review the NEC requirements for conductor sizing and disconnect sizing, I note that the NEC refers to sizing based upon the drive unit rated input current, not the motor current. The Mitsubishi manuals have tables for selecting circuit breakers, but these tables are for 400V 50 Hz installations. The recommendation is also made that high speed fuses be used to provide protection for the drive. My concern is that when I read the sticker on the size of the drive, the only input current rating listed is 61.6 amps. If I follow this, the disconnect cannot be less than 115% of the drive unit rated input current which is: 61.6 * 1.15 = 70.84 amps. This turns out to require a bigger breaker than I anticipated before. I have been looking for documentation with suggestions for protection of this style of Mitsubishi drive, but I do not see anything. Does anyone else here have any experience working with these drives in the past and have any comments?

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Patroit, With the input current rating of the drive, this should be the fuse or circuit breaker rating. The input rating is the maximum current of the drive. I hope this helps, swimmy67

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Actually according to THIS document it should be a 90 Amp Class RK5, but not sure about the difference between the EC and NA.

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I think EC is European Community? and NA is North America? I saw the same 90 amp rating in the Basic manual. It is interesting that the drive sticker shows 61.6 amps. It looks like the 90 amp RK5 is the way to go.

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I don't know if the 61.6 amps includes the power up to charge the capacitors

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Patriot, If you are using a 20 Hp motor then the FR-F740-00310 is the drive to use. Is the 20Hp motor going to be used for a heavy duty application? Then the FR-F740-00380 is the drive to use. Look at the ratings on page 3 of the manual that TW posted a link to. For the drive you are using it lists a 75amp breaker. If you look at the specifications on page 90 you will see the maximum output and the input kva. Base your breaker on these ratings. I have been using Mitsubishi FR-A740 drives and I size the Breaker to the rated amperage on the nameplate. For example I use a FR-A740-00230-UA drive for a 15Hp motor. I install a 50 amp breaker for the drive. The breaker for the Drive has never triped at powerup. The new numbering systems of the Mitsu drives has the current rating in the part number i.e. FR-A740-00230-NA means 23 amps. For the Kw ratings a 11Kw is equal to a 15Hp motor. 15Kw is equal to a 20Hp motor. 18.5Kw is equal to a 25Hp motor. 22Kw is equal to a 30Hp motor. swimmy67

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The 75A breaker looks like it would be fine, since it is at least 115% of the rated current on the drive. 61.6 * 1.15 = 70.84A. A 75 A breaker would work. It looks like the fusing would be at 90A, if I used the fusing.

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