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Pauljm

VSD location in panel

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Hi all,

Due to the heat generated by VSD’s and also the fact that bits of copper can be dropped in to the top of them, i always thought it was good practice to put drives at the top of the panel. Problem with this is all cable entries are from bottom of panel so all EMC motor cables need to go from bottom to top using up space in the duct. Just wondered others thoughts on this as I have seen a few panels lately with the servos and vsd’s at the bottom. The plc’s and control gear seem to handle the heat ok but it’s messing with my head which is best practice? Any thoughts?

Thanks.. Paul 

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In general, I also try to put the high-heat stuff at the top of the cabinet and the PLC at the bottom. Our cable entries are also usually at the bottom. Since our disconnect switch is on the top right corner, we try to route the 480V wiring up along the right side of the enclosure and keep the low voltage stuff to the left.

As a side note, and another reason to keep the PLC nearer the bottom, we had one application where we replaced a PLC-5 chassis with a CompactLogix. The PLC-5 was at the top of the cabinet, right next to the disconnect switch, so that's where the CompactLogix had to go too. After the upgrade was mostly done, we got permission and funds to also replace the old mechanical cam switch with a resolver & in-chassis module. The resolver module ended up right next to the disconnect switch because it was on the end of the chassis and we started having intermittent noise issues. We ended up having to move the resolver module to the left end of the chassis, which messed up all of the I/O wire numbers and addressing. Since it was a quick-turnaround upgrade, we didn't have time to re-label all of the wires, so we just had to put notes on each page of the drawings highlighting the discrepancy. I really dislike leaving stuff like that, but we didn't have much choice in that instance. The AC in/output modules are not nearly as sensitive to the noise, so they work fine being right next to the disconnect. If we ever get a chance to re-do that cabinet, the PLC will move to the bottom, but since that one has a CompactLogix in it, it's not even on the upgrade list right now. It may stay that way until the machine is decommissioned next millennium (it's a Minster press so it will probably keep running until the heat death of the universe...).

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It all depends on how you shape your airflow.

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Yeah. Like NevergoldMel says heat shouldn't be an issue as long as you have airflow past drives. In fact I would say you'd be worse off putting the drive at the top if it doesn't have airflow because the heat won't be exhausted as easily. Doesn't matter much if you have the intake in the bottom or the top with the exhaust at the other side etc if you have large flow fans. If you are only exhausting small amounts of air put the exhaust on the top to take advantage of the small gains from natural convection. Just make sure the airflow crosses the drives. If you want good info on stuff like this look at all the work computer enthusiasts have put in testing airflow with large heat generating components.  I have found that if I have a large diameter intake and exhaust I can get away with no fans even in ambient 32C weather. That's 2x 12" intake/exhaust ports with 12hp worth of 208v drives running full out. Customer wanted to try that rather than paying for a fan. The PLC has been counting any overheat faults and in 2 years he hasn't had 1. 

Personally I always put my drives in a separate box from the logic components. I found that often the price of the larger box was very similar to the cost of the 2 smaller boxes. Just join them up with some large diameter pipe. That way I have good separation from the VFD's noise and it's higher voltages. Usually I'm dealing with 480v drives or large numbers of small 3hp 208v drives though. 

The few times that I have been concerned about objects falling into the drive I have just bent up a piece of metal on a small metal break we made and bolted it above the drive. Paying attention to make sure that I'm not going to have airflow issues.

Edited by Morberis

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Hence the reasoning for doing a heat load calculation for the entire enclosure based upon environmental conditions, heat emitting devices, enclosure size and exposed surface area and the temperature you want to maintain in the enclosure.  Then supplying the appropriate means of air/heat exchange with thoughts about airflow and getting cooler air (intake) to blow across major heat producers.

Next discussion will be surrounding whether the blower should blow air into (positively pressure) or pull air out (negatively pressure) of the enclosure.  After that, you'll want to discuss blower at top or bottom.

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There's a big issue about where to put the intake and exhaust, which I prefer both to be powered, and usually wherever you want to put it will get blocked by where the Engineering firm on your project wants it mounted. 

If it's going to be mounted side by side with other VFD cabinets (which is typical) I'd put the intake low (below the door if possible) and have a air flow tube fabricated to get the air flow close to the backplane of the enclosure or hell behind it and maybe they won't throw the 3 phase cables in the way. Place the Exhaust near the top of the door diagonally across from the intake.

I've seen Eaton Pre-Engineered Drive Panels that had intake across the bottom of the front and Exhaust out the back of the top.

Wherever you put it the Electricians need to be told not to run the 4/O or larger 3 phase in front of the intake or the exhaust or they will every single time.
 

Generally, you'll want to push air in the bottom and out the top, since heat rises and that need to GTFO.
 

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I'm in agreement with Mel.  I prefer pressurizing at the bottom and exhausting at the top.  I also prefer all heat generating devices low in the panel.

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I'm not sure putting the hot stuff at the bottom helps.
Unless you're worried about the other stuff getting cold.

Heat rises normally. 

I general I like putting the Drives in their own box once you start heading upwards of 25 HP and under 30 HP you can usually just order a nice Drive in it's own box from the vendor.
But then I'm weird I like using Ether/IP cards in Motor Drives.

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On 9/12/2019 at 11:29 AM, pcmccartney1 said:

Hence the reasoning for doing a heat load calculation for the entire enclosure based upon environmental conditions, heat emitting devices, enclosure size and exposed surface area and the temperature you want to maintain in the enclosure.  Then supplying the appropriate means of air/heat exchange with thoughts about airflow and getting cooler air (intake) to blow across major heat producers.

Next discussion will be surrounding whether the blower should blow air into (positively pressure) or pull air out (negatively pressure) of the enclosure.  After that, you'll want to discuss blower at top or bottom.

I think that's over complicating it. You shouldn't be designing your heat exchange so close to the margin that you're going to rely on radiated and conducted heat exchange. But you should definitely do a calculation to find out how much heat you are generating and how much airflow you need to have going through at the max ambient temperatures, or above, that the box will experience. Then add in whatever margin you're comfortable with. For the conditions that my boxes experience I always assume that it's 33C.

 

If your box is going to be outside. Make sure it's either shaded or calculate how much heating it will get from the sunlight. It will mess everything right up. I spent 1 summer going around doing changes to all of my predecessors irrigation control boxes. I added shade structures and up-sized the fans for 33C. The existing fans would only be able to handle... 26C. 

 I also always positively pressurize my boxes because I have seen negatively pressurized boxes collect fine dust. But I work in ag where small particles and corrosive gases abound. 

Again I don't think top or bottom really matters as long as you have cross flow of air. It's that direct contact with recently exchanged air that is going to keep your devices cool. Not sitting in it's own pool of stagnant air and heat because there is a natural eddy of air like you get in a truck bed. Maybe that means don't go with a large fan, go with 2 smaller ones and 2 smaller exhausts if the box is large enough. 

 

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