# Air compressor requirements



## spark E (Jul 9, 2015)

Hi guys,

I been asked to quote on a 175hp 600v 3ph Atlas air compressor, no name plate as unit hasnt been ordered yet. Been spending the past few years doing mainly resi so im a bit rusty and hopefully can get some confirmation from you guys.

(CEC).. from my calc, conductors would be 3/O, main breaker 300A with a 400A fusible disconnect fused at 300A. Am I bang on with this or missing something?

Appreciate all the help, got my foot in the door with this company and really dont want to mess this up!

Cheers


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## 460 Delta (May 9, 2018)

Will the run be long or relatively short? Just make sure that the V/D doesn't get excessive.


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## CAUSA (Apr 3, 2013)

The unit will most likely come with a soft start or a VFD. 

Just take in to consideration the ambient temperature of the area for conductor insulation rating 28-100 (3) ii.

Atlas Copco can tell you the temperature of there builds for the landing points. If you cannot get a hold of the manufacturing division for information, The rental division local company of Atlas Copco have the same units and you can get the information from them if you need.

And you might be asked to factor in some control conductor run for a pressure transducer. if not part of the build.


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## spark E (Jul 9, 2015)

460 Delta said:


> Will the run be long or relatively short? Just make sure that the V/D doesn't get excessive.


Thank you, will do the vd calc to make sure.


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## CAUSA (Apr 3, 2013)

spark E said:


> Hi guys,
> 
> I been asked to quote on a 175hp 600v 3ph Atlas air compressor, no name plate as unit hasnt been ordered yet. Been spending the past few years doing mainly resi so im a bit rusty and hopefully can get some confirmation from you guys.
> 
> ...


Forgot to mention,

the unit should come with two motors.

Main drive, for the screw. soft start or VFD depending on manufacture build.

Fan drive for the inter-stage coolers and after coolers, VFD or across the line. 15 to 10HP depending on CFM capacity of the compressor and build design. 

Could be water cooled as well. and not have this extra motor. so just a heads up.


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## spark E (Jul 9, 2015)

CAUSA said:


> The unit will most likely come with a soft start or a VFD.
> 
> Just take in to consideration the ambient temperature of the area for conductor insulation rating 28-100 (3) ii.
> 
> ...


Thanks, will look into temp factor.. unit does have controls built in, just supply requirements.


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## oldsparky52 (Feb 25, 2020)

If you don't have the manufacturer's specs on this, make sure when you quote it, you lay out what you are quoting so you don't get stuck battling the owner with I didn't bid that/you should have known argument.


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## spark E (Jul 9, 2015)

CAUSA said:


> Forgot to mention,
> 
> the unit should come with two motors.
> 
> ...


Wow, I did notice specs on fan motor but thought it was fed via main supply, you are telling me that I would have to run a seperate feed and disconnect for the fan motor?


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## spark E (Jul 9, 2015)

spark E said:


> Wow, I did notice specs on fan motor but thought it was fed via main supply, you are telling me that I would have to run a seperate feed and disconnect for the fan motor?


Havent had my coffee, would just add in the other motor to run I meant.


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## CAUSA (Apr 3, 2013)

spark E said:


> Wow, I did notice specs on fan motor but thought it was fed via main supply, you are telling me that I would have to run a seperate feed and disconnect for the fan motor?


So usually the fan motor is not attached to the compressor skid for a permanent set up it is located in a area. That is set up for air flow requirements set by engineering.

you will have to still factor it in. But the print should tell you if separate feed With a operating contractor.

Or feed from control panel of compressor from the built in relay.

But I think your main conductor size should be ok.
I would get more information and the print for construction should show all information.

Is this a replacement for the customer? If so ask for the old P&ID to look at the old system. To give you a better control scheme. And any prints that you have so you are well armed.

site walk if you can as well.


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## Bourbon County (Aug 19, 2020)

Is this company asking for a hard quote on installing a piece of equipment that has yet to be specified or even ordered, or do they just need a blue sky quote for budgeting purposes? It's likely that this company has to have a $ figure on not only the compressor but the costs for all the work required to install and interface with the plant's compressed air system. This would include the millwrights, fitters, electricians, plus any moving or modifications of existing equipment or systems to accommodate the new compressor. Most companies have to have an all inclusive cost to present to their officers and accountants to get the budget amount approved.

In my somewhat limited experience with Atlas Copco, they are a top notch company with excellent customer support. I'm sure a unit that big will be shipped with a pre built control panel with all controls and power distribution for everything supplied with the compressor package. I think it would be critical to at least find out if the control panel is mounted on the skid with any motors pre wired or if it will be remote mounted in which case you would have to wire from the control panel to any motors and sensors. Atlas is ultimately responsible for the performance, warranty, and reliability of the equipment, wire to their specifications and you should be fine. Of course, you have to have their specifications first.


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## oldsparky52 (Feb 25, 2020)

Bourbon County said:


> Is this company asking for a hard quote on installing a piece of equipment that has yet to be specified or even ordered, or do they just need a blue sky quote for budgeting purposes?


A most excellent question.


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## micromind (Aug 11, 2007)

I think you're looking at a total of around 200 HP with the compressor motor and the cooling fans.

I don't think 3/0 is big enough, I bet it pencils out to 300 CU.

I think the load would be pushing a 300 amp breaker pretty hard, I'd go 350 or 400. Depending on the switchgear, 300, 350 and 400 will be the same frame size.

Further. I would not use a fused disconnect. There's no reason for it plus the fuses are another point of failure. The breaker in the switchgear will provide short-circuit and ground-fault protection and the motor overloads provide overcorrect protection. The fuses don't accomplish anything.


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## micromind (Aug 11, 2007)

spark E said:


> Thanks, will look into temp factor.. unit does have controls built in, just supply requirements.


That's normal, these compressors are called a 'packaged unit'. All you need to do is connect the power to the terminals inside the control panel. 

Some places want controls connected to their PLC system so they know if it's running or faulted. Usually, these are small cables; 18/2 shielded but sometimes it can be an ethernet cable of some sort that has the ability to communicate a bunch of operating data to a computer screen somewhere.


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## paulengr (Oct 8, 2017)

spark E said:


> Hi guys,
> 
> I been asked to quote on a 175hp 600v 3ph Atlas air compressor, no name plate as unit hasnt been ordered yet. Been spending the past few years doing mainly resi so im a bit rusty and hopefully can get some confirmation from you guys.
> 
> ...


Compressor manufacturers play games with specs. You often see goofy nonstandard service factors for instance. They know they need much larger starting than running loads and they also run it into the service factor when loaded using the duty cycle spec, all to use the smallest label motor possible.


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## spark E (Jul 9, 2015)

CAUSA said:


> So usually the fan motor is not attached to the compressor skid for a permanent set up it is located in a area. That is set up for air flow requirements set by engineering.
> 
> you will have to still factor it in. But the print should tell you if separate feed With a operating contractor.
> 
> ...


It is a new unit being added, had a site walk through with specs that show water cooled and max size fusing, found out that hvac is handleing duct work and exhaust.

Thanks for the heads up, I rfp'd today to ensure. Appreciate the info!


paulengr said:


> Compressor manufacturers play games with specs. You often see goofy nonstandard service factors for instance. They know they need much larger starting than running loads and they also run it into the service factor when loaded using the duty cycle spec, all to use the smallest label motor possible.


Yes, the specs compared to my numbers are a head scratcher. Even comparing to code book.. ref table 44 and 45.. do you know why those numbers seem off to calcs?


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## spark E (Jul 9, 2015)

micromind said:


> I think you're looking at a total of around 200 HP with the compressor motor and the cooling fans.
> 
> I don't think 3/0 is big enough, I bet it pencils out to 300 CU.
> 
> ...


I agree about the fused disconnect but it seems as a requirement from Atlas but in works to see if we can talk them out of it. It is vsd compressor, would that not assist in the high demand and low start up? With code at 250% max cb, that is 313amps.. I wouldnt be able to increase cb size any further than 300amps.


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## spark E (Jul 9, 2015)

Bourbon County said:


> Is this company asking for a hard quote on installing a piece of equipment that has yet to be specified or even ordered, or do they just need a blue sky quote for budgeting purposes? It's likely that this company has to have a $ figure on not only the compressor but the costs for all the work required to install and interface with the plant's compressed air system. This would include the millwrights, fitters, electricians, plus any moving or modifications of existing equipment or systems to accommodate the new compressor. Most companies have to have an all inclusive cost to present to their officers and accountants to get the budget amount approved.
> 
> In my somewhat limited experience with Atlas Copco, they are a top notch company with excellent customer support. I'm sure a unit that big will be shipped with a pre built control panel with all controls and power distribution for everything supplied with the compressor package. I think it would be critical to at least find out if the control panel is mounted on the skid with any motors pre wired or if it will be remote mounted in which case you would have to wire from the control panel to any motors and sensors. Atlas is ultimately responsible for the performance, warranty, and reliability of the equipment, wire to their specifications and you should be fine. Of course, you have to have their specifications first.


It isnt a hard quote, exactly what you mentioned, budget to provide officers but at same time wanting to test myself on hard quote as I will be doing a few more on smaller units very shortly. Thanks for sharing your insight with Atlas, these units do seem very high end with only feeders to worry about.


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## CAUSA (Apr 3, 2013)

spark E said:


> I agree about the fused disconnect but it seems as a requirement from Atlas but in works to see if we can talk them out of it. It is vsd compressor, would that not assist in the high demand and low start up? With code at 250% max cb, that is 313amps.. I wouldnt be able to increase cb size any further than 300amps.


Check out 28-200 (4) in the CEC.

This should help.

For your branch circuit, your taking off and existing breaker?

since it is water cooled, the spec for the other motor? is it part of the package? or the equipment for the HVAC exhaust.

hope you get the gig.


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## oldsparky52 (Feb 25, 2020)

I had a boss that would give a 15% higher number on a budget quote and the salesman wanted to go at or under what we thought the job would go for. The salesman said it would keep him in the running and the construction manager didn't want to deal with customer and salesman accusing him of bait and switch.

So, what are the thoughts of this community, me personally, I would figure the job as I would bid it and put 10% on it for "contingencies" (not disclosed to the customer or salesman).


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## spark E (Jul 9, 2015)

CAUSA said:


> Check out 28-200 (4) in the CEC.
> 
> This should help.
> 
> ...


I have to supply new breaker, so have to keep in mind load of panel.. 2- 150A breakers with 3- 30amp breakers on a 600A panel. Yes, the unit comes as a package, its a big guy. Hopefully get it with future work.


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## Malywr (Jan 23, 2018)

spark E said:


> It isnt a hard quote, exactly what you mentioned, budget to provide officers but at same time wanting to test myself on hard quote as I will be doing a few more on smaller units very shortly. Thanks for sharing your insight with Atlas, these units do seem very high end with only feeders to worry about.


Check with manufacture for specks 

In my place we have compressor package 170KW 480v it is closed to 200HP 
And we run 2c -2.5”. 3-300 kcmil CU. Protected 500A and non fuse disco 400A but unit has fuses inside 
Manufacture required line reactor to protect VFD in it 
Contact manufacture for specifications snd when choosing breakers or fuses make sure you pick right size of AIR arc flash that could be expensive


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## Malywr (Jan 23, 2018)

Malywr said:


> Check with manufacture for specks
> 
> In my place we have compressor package 170KW 480v it is closed to 200HP
> And we run 2c -2.5”. 3-300 kcmil CU. Protected 500A and non fuse disco 400A but unit has fuses inside
> ...


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## Bourbon County (Aug 19, 2020)

Yes, the VFD will have everything to do with locked rotor current draw. I'm sure the VFD will be programmed to start from full stop with a nice long ramp up. I'm clueless as to how that factors with feeder and overcurrent sizing under Canadian code. Unless it's shut down for service or a safety device, the initial start-up will likely be the only time it's ever started from a full stop.

Screw compressors are very energy efficient and it's cheaper to keep them running at an idle speed under times of low demand than to stop them completely. They can react fast enough with the VFD to increasing load demands that storage tank(s) aren't required. Storage tanks take up interior real estate which is premium in some plants as well as eliminating the additional piping and whatever periodical inspection requirements are required. I don't know if they've gotten this issue fixed yet or not but the early ones I saw were all made by Sullair and they all leaked oil. 

I would be surprised if Atlas isn't trying to sell them a drier and/or an after cooler to go with this compressor. 

I admire your approach to the bidding. There is always a chance that you are just being used, but you can't win if you don't play. If you are trying to get your foot in the door, they might just be opening it slightly for you. Good luck on this project.


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## Malywr (Jan 23, 2018)

Bourbon County said:


> Yes, the VFD will have everything to do with locked rotor current draw. I'm sure the VFD will be programmed to start from full stop with a nice long ramp up. I'm clueless as to how that factors with feeder and overcurrent sizing under Canadian code. Unless it's shut down for service or a safety device, the initial start-up will likely be the only time it's ever started from a full stop.
> 
> Screw compressors are very energy efficient and it's cheaper to keep them running at an idle speed under times of low demand than to stop them completely. They can react fast enough with the VFD to increasing load demands that storage tank(s) aren't required. Storage tanks take up interior real estate which is premium in some plants as well as eliminating the additional piping and whatever periodical inspection requirements are required. I don't know if they've gotten this issue fixed yet or not but the early ones I saw were all made by Sullair and they all leaked oil.
> 
> ...


This is not part of this conversation 

Dryer is must have in some locations or if equipment is expensive and sensitive to moisture 
After cooler should be part of the package
Storage tank is great addition-to maintain continuous stable pressure and compressor manufacture recommend that it also helps removal of moisture from compressed air in addition to dryer


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## spark E (Jul 9, 2015)

Bourbon County said:


> Yes, the VFD will have everything to do with locked rotor current draw. I'm sure the VFD will be programmed to start from full stop with a nice long ramp up. I'm clueless as to how that factors with feeder and overcurrent sizing under Canadian code. Unless it's shut down for service or a safety device, the initial start-up will likely be the only time it's ever started from a full stop.
> 
> Screw compressors are very energy efficient and it's cheaper to keep them running at an idle speed under times of low demand than to stop them completely. They can react fast enough with the VFD to increasing load demands that storage tank(s) aren't required. Storage tanks take up interior real estate which is premium in some plants as well as eliminating the additional piping and whatever periodical inspection requirements are required. I don't know if they've gotten this issue fixed yet or not but the early ones I saw were all made by Sullair and they all leaked oil.
> 
> ...


Thanks, appreciate the info and well wishes.


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## micromind (Aug 11, 2007)

spark E said:


> It is a new unit being added, had a site walk through with specs that show water cooled and max size fusing, found out that hvac is handleing duct work and exhaust.
> 
> Thanks for the heads up, I rfp'd today to ensure. Appreciate the info!
> 
> Yes, the specs compared to my numbers are a head scratcher. Even comparing to code book.. ref table 44 and 45.. do you know why those numbers seem off to calcs?


Since it's water cooled, there's most likely just the compressor motor, these units rarely have a water pump. They use the plants cooling water or city water both of which are already pressurized. 

This is NEC, CEC may or may not be the same..........If there's a VFD then the code requires the conductors that feed it to be rated at 125% of the rated input of the VFD, regardless of the size of the motor. 430.122(A). The VFD input will likely be somewhere around 240 amps so you'll need 300 amp wire which, oddly, is 300 MCM. 

This gets tricky, 3 - 3/0s will fit in a 2", 3 - 300s will fit in a 2" according to code but I think it'd be a pretty tough pull. I'd use 2 1/2". 

Remember, the above is based on the NEC.


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## paulengr (Oct 8, 2017)

spark E said:


> It is a new unit being added, had a site walk through with specs that show water cooled and max size fusing, found out that hvac is handleing duct work and exhaust.
> 
> Thanks for the heads up, I rfp'd today to ensure. Appreciate the info!
> 
> Yes, the specs compared to my numbers are a head scratcher. Even comparing to code book.. ref table 44 and 45.. do you know why those numbers seem off to calcs?


You need to go by the FLA/FLC the compressor is labeled as. As I said they know they need more torque for starting and they know duty cycle has a huge impact on rated current so they try to either give you what looks like a strange motor name plate or a separate name plate. Wye delta or electronic soft starters are standard on larger units.

By the way Atlas Crapco has one of the worst service contracts in the industry, air ends only last about 40,000 hours, and their controls are afflicted by evil spirits (full of bugs). That’s being pretty nice. Get yourself a Gardner Denver, Sullair, or Elliott. You won’t be sorry! They are that bad.


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## spark E (Jul 9, 2015)

paulengr said:


> You need to go by the FLA/FLC the compressor is labeled as. As I said they know they need more torque for starting and they know duty cycle has a huge impact on rated current so they try to either give you what looks like a strange motor name plate or a separate name plate. Wye delta or electronic soft starters are standard on larger units.
> 
> By the way Atlas Crapco has one of the worst service contracts in the industry, air ends only last about 40,000 hours, and their controls are afflicted by evil spirits (full of bugs). That’s being pretty nice. Get yourself a Gardner Denver, Sullair, or Elliott. You won’t be sorry! They are that bad.


Never heard a bad thing about Atlas till now, choice is out of my hands.. got in with an Atlas salesmam so gotta go with what he gives. Thanks though


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## spark E (Jul 9, 2015)

micromind said:


> Since it's water cooled, there's most likely just the compressor motor, these units rarely have a water pump. They use the plants cooling water or city water both of which are already pressurized.
> 
> This is NEC, CEC may or may not be the same..........If there's a VFD then the code requires the conductors that feed it to be rated at 125% of the rated input of the VFD, regardless of the size of the motor. 430.122(A). The VFD input will likely be somewhere around 240 amps so you'll need 300 amp wire which, oddly, is 300 MCM.
> 
> ...


Thanks man, appreciate it


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