# Motor Control cabinets and VFD



## Metersocket648 (Feb 8, 2021)

So I went into a sawmill on a call to install a new motor control cabinet and a VFD, the motor is for a new bandsaw they have ( actually the equipment has 3 motors, bandsaw motor, bark stripper, and horizontal saw) so that want 3 VFDs and one controller cabinet, now In my experience with VFDs and cabinets I would just have my cabinet, all the control wiring and the VFD with it, they want 1 cabinet but they have 3 VFDs, what would be the most efficient way of going about putting the 3 drives and the control wiring in the same cabinet without making a quagmire of wires?? ( I already know some of you will say zip ties and cable ties but I’m talking about sectioning the 3 different drives with their own control wiring in the same cabinet.


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## Jlarson (Jun 28, 2009)

Finger duct.


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## gpop (May 14, 2018)

Set the vfd's with the required space. Add a main breaker, 3 sub breakers and 3 finger safe fuse blocks then fill in the gaps with panduit and din rail. Once you have all the crap you need in the cabinet like control transformer and relays space maybe at a premium so i wouldn't worry about keeping things separate.


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## wiz1997 (Mar 30, 2021)

Here's a control box with just two VFD's and a vibrating conveyor controller I "cleaned up" a few weeks ago.

Plenty of air circulation around the VFD's is a must.
Mounting VFD's on DIN rail provides a little air circulation around the back.
Not all can be mounted on DIN rail.

Panduit keeps things neat.

Before clean up.








After









Just one of the panels I have on my list to clean up.

It's amazing how the maintenance mechanic electrician want-to- be's can mess up a panel.

Air circulation around the VFD's is the most important thing.
Plenty of room in the box.

We have installed air circulating fans and exhausts in most of our panels to aid in cooling.
Just remember the air filters must be changed regularly if in a dusty area.
Some panels with temperature sensitive equipment have vortex air coolers, which are air hogs IMO.

Another item to consider is having a place to land the shields of the motor conductors.
You can see the bar just below the terminal strips where the shields are attached and then that bar in bonded to ground.


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## John Valdes (May 17, 2007)

Draw a schematic as to the wiring scheme. This will be needed for control wiring (build the panel) and to make a material list. Make sure it all works on paper before you pick up one tool. Order an enclosure larger than you will need. You will be surprised at how much room you thought you would have to find out its to small.
Lay out, arrange all devices and wire channel on the removed back board. Wire channel is your best bet. TyRaps are not a good idea at all.
Once you have built your panel bench test it. Make sure everything does what its supposed to do.
Its very important to utilize a terminal strip at the bottom. Here you can land external (machine and peripheral) wires. So then all you have to do when you are ready to mount is connect wire by number to the terminal strip. 
I have never used VFD wire, so I am not familiar with the shielding.


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## JRaef (Mar 23, 2009)

NEVER run the VFD output wires in any duct or conduit with any other wires. The best way to accomplish this in a panel is to mount the VFDs toward the bottom so that the output wires go right into their conduits.

Heat x time = failure in electronics. VFDs are at best 97% efficient, so 3% of the power they control will become heat in the box. That means either a LOT of fresh air flow or an air conditioner. In a sawmill, fresh air flow pulls in sawdust, which can be corrosive to the electronics in the VFDs. Keep that in mind. You don’t say the HP sizes, but if they are all small, like 5HP or less, then you might be able to get away with a sealed enclosure. My rule of thumb is to look at the manufacturer’s size for a NEMA 1 enclosed drive, then quadruple the volume (does not work for outdoors if exposed to direct sunlight). So for 3 VFDs, add up the volumes of their individual N-1 enclosures, then multiply by 4, then back out any restrictions like depth and height. The box might end up huge, but it’s the only possible way to avoid sucking in dust or paying for an air conditioner.


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## MoscaFibra (Apr 15, 2021)

JRaef said:


> NEVER run the VFD output wires in any duct or conduit with any other wires. The best way to accomplish this in a panel is to mount the VFDs toward the bottom so that the output wires go right into their conduits.
> 
> Heat x time = failure in electronics. VFDs are at best 97% efficient, so 3% of the power they control will become heat in the box. That means either a LOT of fresh air flow or an air conditioner. In a sawmill, fresh air flow pulls in sawdust, which can be corrosive to the electronics in the VFDs. Keep that in mind. You don’t say the HP sizes, but if they are all small, like 5HP or less, then you might be able to get away with a sealed enclosure. My rule of thumb is to look at the manufacturer’s size for a NEMA 1 enclosed drive, then quadruple the volume (does not work for outdoors if exposed to direct sunlight). So for 3 VFDs, add up the volumes of their individual N-1 enclosures, then multiply by 4, then back out any restrictions like depth and height. The box might end up huge, but it’s the only possible way to avoid sucking in dust or paying for an air conditioner.


There's a few options for cooling, if the environment is that dusty I agree, avoid filters as they never get changed. Especially if there is no dedicated maintenance team...and even then those are iffy. 

There are chillers you can get that aren't stupid expensive, but it depends on what your customers budget is. You can also look at Vortex chillers if they have a ton of compressed air around it. They are loud, and bleed air constantly but they do work at keeping things cool.


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## paulengr (Oct 8, 2017)

MoscaFibra said:


> There's a few options for cooling, if the environment is that dusty I agree, avoid filters as they never get changed. Especially if there is no dedicated maintenance team...and even then those are iffy.
> 
> There are chillers you can get that aren't stupid expensive, but it depends on what your customers budget is. You can also look at Vortex chillers if they have a ton of compressed air around it. They are loud, and bleed air constantly but they do work at keeping things cool.


Bad idea both ways. Have you seen an air conditioner survive a plant environment more than 2 years? Me neither. And that vortex cooler works at a whopping 12.5% efficiency. One watt of cooling for every 8 you put in it!! Might be ok for say a screen but not a VFD.

Ok so up to around 2-3 kW you can use a thermoelectric cooler. Same as AC but there are just 3 parts. Two are muffin fans. The third is a heat moving transistor…no moving parts. Apply power and one side gets cold and the other hot. No compressor, no Freon, no leaks. They last for 10+ years. Slightly less efficient than AC but the prices get out of sight quickly. So it’s a reasonable solution up to 25 HP of VFDs.

Second solution…air to air heat exchanger. Similar to the thermoelectric cooler but it only has the fans so it’s basically a very passive device…an amped up radiator. So again lasts a very long time. Gets you up to around 100 HP or so.

Both devices bolt to the sides of the cabinet and are 100% sealed. Air flows on either side, NOT through it. No filters to plug up. Maybe hit it with an air line to blow it out occasionally.

Aside from that based on the description I would not use a VFD for most of that. Just got through with a 200 HP band saw in the past six months. Accelerated to speed in about 20 seconds on a heavy duty rated soft start equipped with an SCR style DC injection brake so it stops in under 20 seconds too. Set soft ramp to 500-600% of FLA current limiting in 5 seconds, starting at 300% FLA, and it will start right up. I can stop in 10 seconds but it tends to make it hard to keep the belts tight.

On bark hoggers/chippers you can do the same thing but my experience is you just can’t regeneratively or DC injection brake long enough to stop. At best you cut stopping time to 25%. Just way too much inertia. Fastest way to stop is stick a log in it.


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## Southeast Power (Jan 18, 2009)

I just went through this with 3-5 hp VFDs.
With no ventilation,
They each required a 24”x24”x12” cabinet or all three in a cabinet the size of a refrigerator.
I asked the engineer to approve the use of a Danfoss/Trane TR 200.


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## JRaef (Mar 23, 2009)

> … vortex cooler works at a whopping 12.5% efficiency. One watt of cooling for every 8 you put in it!! Might be ok for say a screen but not a VFD.


I once did a PLC panel over a pot line at an aluminum plant, the pots are where they melt the bauxite ore. We used a small vortex cooler to keep it cool and hooked it up to their existing instrument air line coming from a 40HP compressor. They had to up the HP to 50HP to deliver the volume and pressure necessary.


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## MoscaFibra (Apr 15, 2021)

JRaef said:


> I once did a PLC panel over a pot line at an aluminum plant, the pots are where they melt the bauxite ore. We used a small vortex cooler to keep it cool and hooked it up to their existing instrument air line coming from a 40HP compressor. They had to up the HP to 50HP to deliver the volume and pressure necessary.


I don't like them, but it was stuck in the panel on top of a massive reheat furnace....and kept that PLC and drive rolling. Is it good? No. Is it the best? No. Did it work. At least for the past 20 years. The ambient up there would be 50-55 regularly on a cool summer day much less a hot one. They are awful with efficiency though.


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## John Valdes (May 17, 2007)

We had serious dust and heat issues in a couple panels outside. There was an inch or more of dust on every surface. They did a second seed picking for cotton fiber. So dusty is an understatement.
We tried a vortex cooler valve in one of the panels to see how it would do. Withing a day or so, the dust inside the panel was now mud. Much worse than just plain dust.
While vortex cooling valves worked good where less dust was present, it still cause condensation in almost any panel we put them in.
This was many years ago, so hopefully the newer vortex cooling valves do not have the same issues as the older models.


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## JRaef (Mar 23, 2009)

John Valdes said:


> We had serious dust and heat issues in a couple panels outside. There was an inch or more of dust on every surface. They did a second seed picking for cotton fiber. So dusty is an understatement.
> We tried a vortex cooler valve in one of the panels to see how it would do. Withing a day or so, the dust inside the panel was now mud. Much worse than just plain dust.
> While vortex cooling valves worked good where less dust was present, it still cause condensation in almost any panel we put them in.
> This was many years ago, so hopefully the newer vortex cooling valves do not have the same issues as the older models.


You have to use compressed air that has gone through an oil separator and a dryer, which decreases the efficiency even more. Then the air dryer is like a dehumidifier, needing regular maintenance to deal with the accumulation of condensate. That’s why I used their instrument air line, it already had those things. Unless it’s something extreme, I find the vortex coolers too difficult to work with; solve one problem, create 3 more...

I've always liked the concept of the thermo-electric (Peltier Effect) coolers, I just wish they were not so expensive when you need a lot of cooling, like for VFDs.


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## micromind (Aug 11, 2007)

I've installed a basic fan somewhere clean, like on the roof, and ducted it into the cabinet. It's not cold air but it's cleaner than inside the building. Plus, you can get a lot of air if needed.


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## paulengr (Oct 8, 2017)

With metal plants, glass, etc., here is another solution.

Heat transfer by radiation is very efficient. The heat transferred is proportional to the 4th power of the temperature difference. It’s why you can be toasty standing next to a camp fire in freezing cold weather.

BUT it also depends on a property called emissivity. It’s why black colored objects absorb heat and space blankets for example reflect it. The emissivity of most metals is around 0.5 to 0.8 so they don’t reflect much. BUT aluminum is a different matter. Emissivity is 0.03! So a trick you can use it put a couple standoffs or even a couple pieces of strut on a cabinet and mount tin (actually aluminum) siding on it. Two layers will knock 600-1000 F down to 10-20 degrees over ambient. This is MUCH more effective. Works as long as you have the “campfire” situation. Also works with stainless in sunlight but the n an outright lean to or awning is better since it also keeps some rain off. Also if you have to AC for environment even spray foam does wonders. You can buy the stuff in big bulk boxes from McMaster if it’s more than a great stuff can but not enough for a spray foam contractor.

If you work around kilns, foundries, steel Mills, aluminum, etc., long enough you get good at heat management. I started just telling vendors to send me equipment and I would fix it.


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