Use nameplate ratings on motor or VFD??
Use nameplate ratings on motor or VFD??
(OP)
I have A VFD capable of running a 1 hp motor but will only be using a 1/2 Hp.
I'm running 208vac, 3 phase, 60 Hz
Motor nameplate states 2.21A @ 208vac
VFD nameplate states 8.2A @ 200-230vac
For the purpose of load calculations and sizing supply conductors, OCPD, and other peripherals, would I use the nameplate ratings of the motor or the VFD? I would usually use the larger, but where there is a large discrepancy between the two, I'm looking for insight on the proper way.
Thank you!
I'm running 208vac, 3 phase, 60 Hz
Motor nameplate states 2.21A @ 208vac
VFD nameplate states 8.2A @ 200-230vac
For the purpose of load calculations and sizing supply conductors, OCPD, and other peripherals, would I use the nameplate ratings of the motor or the VFD? I would usually use the larger, but where there is a large discrepancy between the two, I'm looking for insight on the proper way.
Thank you!





RE: Use nameplate ratings on motor or VFD??
Is that right?
RE: Use nameplate ratings on motor or VFD??
The supply conductors for equipment (VFD) is based on nameplate current. The minimum is #14 AWG.
Load will be based on nameplate current of the VFD. The starting surge and the over load current of the VFD will be based on the nameplate values.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Use nameplate ratings on motor or VFD??
The application is an industrial machine with multiple motors/vfd's with one control cabinet. I sould have included more information as to where I was headed with this.
1.For the supply conductors to the machine, which rating would I use to calculate the load? I know to use 125% of the largest motor in this calc but of which value, 8.2A or 2.21A?
Questions on the control cabinet nameplate data i need to display on the cabinet:
2. For full load current rating of the machine, would I add the above mentioned motor as 8.2A or 2.21A?
3. Say this was the largest motor. Would I specify largest motor rating on this nameplate as 8.2A or 2.21A?
Thanks Again!
RE: Use nameplate ratings on motor or VFD??
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Use nameplate ratings on motor or VFD??
RE: Use nameplate ratings on motor or VFD??
For OCPD of a feeder to the the input of a VFD should the input current rating of the VFD be used or should 125% of the input current rating be used?
RE: Use nameplate ratings on motor or VFD??
Depending on the type/make of VFD, the settings you input of the motor nameplate data will determine the necessary protection the VFD can provide to the motor, if it is a lower rating to the VFD. Some VFD's will have electronic thermal overload (built in) that will be certified by UL for single motor protection.This is wholly based on the user putting the correct motor details into the VFD.
If you do not do this, then you must use an additional thermal overload for the motor to ensure you have motor protection, or if you have multiple motors on the output then you need to have additional form of thermal overload and cannot rely on the in-built protection the VFD can provide.
RE: Use nameplate ratings on motor or VFD??
2. For full load current rating of the machine, would I add the above mentioned motor as 8.2A or 2.21A?
3. Say this was the largest motor. Would I specify largest motor rating on this nameplate as 8.2A or 2.21A?
Thanks Again!
RE: Use nameplate ratings on motor or VFD??
But it's all relative as well. If the VFD requires an OCPD that is SMALLER than what would protect the conductors, you must go with that. That would be stated in the VFD installation guidelines. So for example, you may use 14ga wire that is technically rated for 15A, but the VFD manual may say that you must have a 10A fuse in front of it. If that's the case, the 10A is not violating the NEC because it is LOWER than the conductor protection, so no problem. If on the other hand the VFD manual said to use a minimum 30A fuse or breaker, and you ran 14ga wire, you cannot protect that wire with a 30A breaker, you must use a 15A. Either that or run 10ga wire. The 10ga wire is of course a LOT larger than the minimum 125% of the VFD input current, so no problem there.
For the conductors going TO the motors, follow the standard NEC rules for motor conductors, i.e. 125% of FLC of 2.21A. The Motor Thermal Overload protection of the VFD is protecting those conductors.
If you have more than one motor behind the VFD, you technically need new Short Circuit protection for the conductors as well. You were not clear as to how many VFDs vs how many motors you have.
For the FLC rating of the machine, you would need to base it on the FLC rating of the VFD, the 8.2A. but for the "largest Motor" rating, I would use the actual motor value. That information is somewhat useless anyway, so just follow the exact wording.
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