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Discussion Starter · #1 ·
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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Ready Mix concrete plant electrician
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Will the run be long or relatively short? Just make sure that the V/D doesn't get excessive.
 

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Sub transient reactance X”d worshiper.
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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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Sub transient reactance X”d worshiper.
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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
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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Discussion Starter · #6 ·
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.
Thanks, will look into temp factor.. unit does have controls built in, just supply requirements.
 

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Discussion Starter · #8 ·
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.
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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Discussion Starter · #9 ·
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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Sub transient reactance X”d worshiper.
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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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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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Bilge Rat
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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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Bilge Rat
motors and controls.........
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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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Chief Flunky
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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
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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Discussion Starter · #16 ·
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.
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!
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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Discussion Starter · #17 ·
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.
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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Discussion Starter · #18 ·
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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Sub transient reactance X”d worshiper.
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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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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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