Where to put VFD drive?

[Designer69]

We are replacing some 5hp motors and removing the old starters/breakers from the MCC buckets.

These motors are being replaced with new ones, VFD controlled.

The MCC buckets will just get a breaker in them, however, typically where do you put the VFD drive, inside the MCC bucket next to the breaker?


Or do you put them locally near the motor somewhere? These motors are about 30 feet away from the MCC.


Thank You

 

[Jraef]

You cannot "legally" put them in the MCC yourself, the only power devices that can go in MCCs are those built by the MCC mfr. That doesn't mean it can't be done, but you would be voiding the UL listing of the entire MCC. After an MCC is installed, the only people who might care are the insurance carrier for the facility, but that's not a trivial issue.

Aside from that, there are technical issues that will probably make it untenable; heat being the worst one. VFDs designed to be in MCCs have had a LOT of testing done by the MCC mfr with regard to heat rise, not only for the VFD cubicle, but also for the entire MCC itself. There is also the issue of the SCCR; putting it in the MCC may result in not being able to claim an SCCR that is at or above your available short circuit current in the MCC.

I would hang them on a wall between the MCC and motor if it were me.

 

[Designer69]

Ok thank you. Sounds good


Lastly, is an MCP (Motor ckt protector) only sufficient for protection of the VFD or do I need to install a thermal-mag ckt. bkr in there?


Very lastly, regarding enclosure for the vfd drives... (these are in mech. room, uncovered to elements). Nema 4x cabinet with enough space for the VFD's and controls, unistrut anchored to cmu wall?

Thanks

 

[Jraef]

Ok thank you. Sounds good


Lastly, is an MCP (Motor ckt protector) only sufficient for protection of the VFD or do I need to install a thermal-mag ckt. bkr in there?

Replace it. There is NO legal use for an MCP outside of a factory assembled combination motor starter. They cannot be used as a feeder in any way, shape or form.
It used to be, a few years ago, that a manufacturer could use an MCP on a factory built VFD or Soft Starter, that is no longer the case, UL started disallowing that in about 2005.

Very lastly, regarding enclosure for the vfd drives... (these are in mech. room, uncovered to elements). Nema 4x cabinet with enough space for the VFD's and controls, unistrut anchored to cmu wall?

Thanks

The VFD rejects about 3% of the power going through it as heat, so if you seal it up in a NEMA 4 box, it can cook itself pretty fast. If it's small, I have been able to get away without venting by taking the volume of a manufacturer's NEMA 1 enclosed drive and quadrupling it. So for example if a NEMA 1 drive is 10 x 8 x 14, that's 1120 cu. inches, so I use a sealed enclosure that is at least 4480 cu. inches. But this is dependent on the environment being relatively cool, as in at least 25deg.F less than the max rating of the VFD. So if the VFD is rated for 40C, that's 104F so your environment needs to be no more than 79-80F consistently, in other words an air conditioned space. If the area where you want to put the drive gets to 100F, the drive will cook itself no matter what and you will need an A/C or a lot of ventilation. Some drives however come with an option to shove the heat sinks out of the back of the box, that takes 90% of the heat out of it. If your drives have that option, do that.

 

[drktmplr12]

can confirm everything jraef has said is 100% accurate. very good stuff. :thumbsup:

if you can get those VFD's into a conditioned electrical space and locate disconnects at the motor, that would be ideal.. in my opinion.

 

[Jraef]

And if you put disconnects at the motor, run a couple of control wires to an aux contact of the disconnect that then get wired to the Enable input of the VFD (assuming it has one) so that if someone pulls the disconnect handle while the drive is running, it disables the drive before the main disconnect contacts open.