VFD in existing MCC

[Shoe]

I have a client who wants a VFD put into an existing MCC. It's an R1 frame (7.5HP) VFD. Is it possible to do this? I typically would not put a VFD in an MCC, rather have a fusible disconnect in the MCC feed the VFD mounted near the motor, but the client is insistent on having it in the MCC.

Assuming I have the bucket space in the MCC, how would this work?

 

[Jraef]

I have a client who wants a VFD put into an existing MCC. It's an R1 frame (7.5HP) VFD. Is it possible to do this? I typically would not put a VFD in an MCC, rather have a fusible disconnect in the MCC feed the VFD mounted near the motor, but the client is insistent on having it in the MCC.

Assuming I have the bucket space in the MCC, how would this work?

How important is it to adhere to the rules?

If it is important, you CANNOT put a VFD in an MCC, unless it is a VFD that was designed, tested and listed BY THE MCC MFR to retrofit into their MCC. Given that you mention an "R1 Frame" I will assume it is an ABB ACS550 drive. ABB only released their line MCCs this year, so I would hazard a guess that you do not have an ABB MCC. So if it is any other brand, there is no legal way for you to mount a VFD in it and maintain the UL listing and Short Circuit rating of the MCC. And with an MCC, the SC rating for the entire MCC cannot be greater than the lowest rating of any unit in it. So even if you accept the concept of the "courtesy" 5-10kA rating you can have for something untested, that low rating will extend to all other parts of that lineup.

That's not to say it is not done all the time, because it is. If the job is not going to be inspected, and the company's insurance policy has no requirements for using only UL listed equipment, you can do what you want.

Without testing though, you are kind of on your own for what it is going to take to do it, especially with regards to heat rise testing. One trick you could do though is to get a quote from ABB for a single section of THEIR new MCC with that specific drive in it and see what size cubicle they would use. It's not perfect because you don't know if your MCC will have the same air flow, but it's a good place to start.

Or if the existing MCC is not too old, you could just forgo the ABB drive and get a legal add-on bucket from the original mfr. If by chance it is a Rockwell (Allen Bradley) MCC, the age would not matter.

 

[Shoe]

Thanks. Great reply. I think they have compliance people who walk through the facility routinely and do not know what they are doing.

The compliance people see a VFD outside the MCC and see it as an "arc flash hazard". I've tried explaining that you have a greater arc flash hazard by putting the VFD in the MCC, but it went over their heads.

I'll talk to the MCC manufacturer and get some backup from them on why it is a bad idea (the VFD is bought already, so getting something UL listed is probably not an option).

 

[Besoeker]

I have a client who wants a VFD put into an existing MCC. It's an R1 frame (7.5HP) VFD. Is it possible to do this? I typically would not put a VFD in an MCC, rather have a fusible disconnect in the MCC feed the VFD mounted near the motor, but the client is insistent on having it in the MCC.

Assuming I have the bucket space in the MCC, how would this work?

Not being from your neck of the woods, I can't comment on compliance matters.
But it is feasible from a technical/engineering perspective - it's something we do on a regular basis.
One piece of advice - make sure there is adequate ventilation for the VFD. That's very important.

 

[weressl]

I have a client who wants a VFD put into an existing MCC. It's an R1 frame (7.5HP) VFD. Is it possible to do this? I typically would not put a VFD in an MCC, rather have a fusible disconnect in the MCC feed the VFD mounted near the motor, but the client is insistent on having it in the MCC.

Assuming I have the bucket space in the MCC, how would this work?

Both Jraef's and Besoeker's comments are excellent and spot on as usual.

I would like to add that the use of MCC's for ASDs is rather wasteful as they require a lot of space that can be used for regular starters. If the Owner is concerned about arc-flash then installing a non-UL listed component would also increase the potential of a fault, increase the heat loading of the MCC, regardless of how well the ventillation is provided.

I usually just slap in a breaker into the MCC and rack- or wall-mount the ASDs. Done two (A/B) 200HP ABB last week and the bolt-on only restriction of AB 400A breakers is a POA, we could not provide the separate MCC feed because the Department could not facilitate a shutdown. It was funny to look the 30HP old built-up drives next to the new 200HP new drives. Both of the new drives would easily fit the 30HP cabinet with plenty of room left.

 

[petersonra]

We often use AB MCCs with drives in them as some of our customers insist on doing so. It is a very expensive way for us to supply drives.

The heat issues cannot be easily dealt with for larger drives mounted in an MCC. The only practical way to deal with the heat generated by large drives in a high ambient temperature area is to exhaust the heat directly to the outside of the enclosure by mounting it on the back wall and extending the heat sink thru the back wall of the enclosure and that cannot be done in an MCC.

For smaller drives it is just about money. For larger drives, depending on the ambient temperature where the MCC is located, it may not even be possible to push enough air through the compartment to exhaust the heat.

I will point out that AB makes an accessory cabinet that can be bolted on to an MCC. It is the same size and color and looks like part of the MCC but is UL listed as an industrial control enclosure. We often install PLCs and other control gear in such cabinets. I suspect other MCC makers have a similar such cabinet that might come in handy.

 

[Jraef]

Re: Arc Flash

Since you already have the VFD and need to use it, the better method with regards to Arc Flash hazard mitigation is what you first thought: put a feeder in the MCC and mount the VFD as close to the motor as possible; add a Line Reactor as well. The extra circuit impedance will lower the Available Fault Current at the VFD and lessen the Incident Energy inside the cabinet. Having vents can make that somewhat pointless if someone has to stand in front of the VFD, but I think that ABB offers a "flange kit" that would allow you to shove the heat sinks out the back of a box so that you could use a sealed enclosure.

Just putting the VFD in the MCC will not lower the Arc Flash risk at all. The only advantage to that is that if the MCC is already in a limited access room, you can avoid having people being in the area unless qualified to work there. Doesn't change the risk, but it limits exposure TO the risk.

 

[Besoeker]

For larger drives, depending on the ambient temperature where the MCC is located, it may not even be possible to push enough air through the compartment to exhaust the heat. /QUOTE]
We use inlet fan(s) and outlet filters. The fans also have filter mats so the IP rating is maintained.
I don't know whether that meet the compliance requirements there.

 

[Shoe]

Thanks, everyone. I'll be archiving this page and saving it for future reference... good stuff.

 

[petersonra]

For larger drives, depending on the ambient temperature where the MCC is located, it may not even be possible to push enough air through the compartment to exhaust the heat.

We use inlet fan(s) and outlet filters. The fans also have filter mats so the IP rating is maintained.
I don't know whether that meet the compliance requirements there.

I just did a job with 14 200 HP drives.

The spec the customer gave us claimed the max ambient temp where the drives are located was only 5 deg C lower than the max ambient temp the drives are allowed. You have to push a lot of air to keep the temp rise to 5 deg C even with the drive heat sinks located outside of the cabinet.

each drive still puts 492W of heat into the cabinets along with 2876 W outside. think about how much air you would have to push per drive if you only had a 5 Deg C window and almost 3400W of heat to get rid of per drive.

The fan vender suggested having an inlet and an outlet fan. They said you get about double the air flow of a single fan less about 10% that way.

 

[Besoeker]

each drive still puts 492W of heat into the cabinets along with 2876 W outside. think about how much air you would have to push per drive if you only had a 5 Deg C window and almost 3400W of heat to get rid of per drive.

About 1200CFM by my calcs. Two appropriately sized inlet and two outlet fans would readily cope with that.
As it happens, we did such a project at the back end of last year although we had a 10degC window.

 

[Besoeker]

I just did a job with 14 200 HP drives.

The spec the customer gave us claimed the max ambient temp where the drives are located was only 5 deg C lower than the max ambient temp the drives are allowed. You have to push a lot of air to keep the temp rise to 5 deg C even with the drive heat sinks located outside of the cabinet.

each drive still puts 492W of heat into the cabinets along with 2876 W outside. think about how much air you would have to push per drive if you only had a 5 Deg C window and almost 3400W of heat to get rid of per drive.

The fan vender suggested having an inlet and an outlet fan. They said you get about double the air flow of a single fan less about 10% that way.

Test post - thread says that there are two pages but I can't get to page 2. And now I can. Odd....

 

[petersonra]

Test post - thread says that there are two pages but I can't get to page 2. And now I can. Odd....

I have noticed this happens on occassion when there is only one post on the second page.

Your post was the first one. I could not get to it by clicking on the page 2 link but could get to it by working backwards from your profile. I could see the header for it, but not the post itself.

 

[Besoeker]

I have noticed this happens on occassion when there is only one post on the second page.

Your post was the first one. I could not get to it by clicking on the page 2 link but could get to it by working backwards from your profile. I could see the header for it, but not the post itself.

Glad it's not just me.