Air compressor 200hp

[dm9289]

During a maintenance window a contractor installed a 200hp air compressor. After we got up and running I looked over the install before commissioning and I believe the wire installed is incorrect. Can someone double check me. 3 Cables plus gnd in conduit along beams and wall no other electric.

200hp compressor unit label 293 Fla/ 480 v
My math 293x 125%=366amp 500kcm copper 380 amps @75c.

Contractor ran 4/0 DLO aka NEC RHW-2 flex.
I see that as 230 amp at 75C.
Contractor said that is special high capacity cable and is why it was selected. Am I missing something here??????

Please straighten me out

 

[don_resqcapt19]

No, the contractor does not understand that the typical published ampacity of that cable is based on operation at 90°C and in free air, neither of which will apply to your installation.

 

[dm9289]

No, the contractor does not understand that the typical published ampacity of that cable is based on operation at 90°C and in free air, neither of which will apply to your installation.

I think sometimes the DLO cut sheets market this cable as 405amps.
Perhaps there is a common free air purpose for it in mines or other applications.

 

[dm9289]

No, the contractor does not understand that the typical published ampacity of that cable is based on operation at 90°C and in free air, neither of which will apply to your installation.

I informed the supervisor of my concern, this was my last working day. Short version odd rotating shifts. Commissioning was planned for next day which I advised against,they did it with the compressor vendor anyhow. How long till this overheats and melts realistically, or will it be fine?

 

[don_resqcapt19]

I think sometimes the DLO cut sheets market this cable as 405amps.
Perhaps there is a common free air purpose for it in mines or other applications.

In my opinion it is simply marketing intended to mislead.

 

[kwired]

I informed the supervisor of my concern, this was my last working day. Short version odd rotating shifts. Commissioning was planned for next day which I advised against,they did it with the compressor vendor anyhow. How long till this overheats and melts realistically, or will it be fine?

That "realistically" needs to factor in actual loading, duration of loading, duration of peak demands, cooling off times, ambient temperatures, etc.

Termination temps is likely where first signs of failure will occur as long as there is no extreme ambient conditions over the run.

 

[dm9289]

That "realistically" needs to factor in actual loading, duration of loading, duration of peak demands, cooling off times, ambient temperatures, etc.

Termination temps is likely where first signs of failure will occur as long as there is no extreme ambient conditions over the run.

This is in a steel mill 24/7 the main compressor. It appears to be a Wye/ delta start. The motor is not speed controlled and will likely run 24/7 other components that make up 48a of the 293a load im not certain how they work but package rating is 293a

 

[zbang]

It would be interesting to go back after a month of operation with an IR camera.

 

[kwired]

This is in a steel mill 24/7 the main compressor. It appears to be a Wye/ delta start. The motor is not speed controlled and will likely run 24/7 other components that make up 48a of the 293a load im not certain how they work but package rating is 293a

But how much is it loaded and does that vary?

If it is only putting out about 100 HP the majority of the time those conductors are (realistically) probably sized about right for the actual load and may last for a very long time. Occasional peaks over this will cause more heating but how much and how long are important. POCO's kind of use same approach at sizing conductors and even transformers. NEC basically says these conductors need to assume the motor is capable of delivering 200 HP indefinitely, and we typically need to size them at 125% of that level.

 

[dm9289]

But how much is it loaded and does that vary?

If it is only putting out about 100 HP the majority of the time those conductors are (realistically) probably sized about right for the actual load and may last for a very long time. Occasional peaks over this will cause more heating but how much and how long are important. POCO's kind of use same approach at sizing conductors and even transformers. NEC basically says these conductors need to assume the motor is capable of delivering 200 HP indefinitely, and we typically need to size them at 125% of that level.

How much it varies I can’t reliably predict

 

[kwired]

How much it varies I can’t reliably predict

I understand, but at same time you probably know more what the air demands may be than I would having never seen what it all supplies.

Just because the system is at pressure doesn't mean it is drawing rated power, the more air actually being used by items in the plant will increase motor draw. There is a chance this is oversized to allow some additions or even quick recovery as well so even if air demand is at maximum level doesn't mean your compressor is pulling maximum rating.

This all getting at your initial question containing the word "realistically". NEC still requires a conductor able to handle the rating of the motor whether it is fully loaded or not.

 

[retirede]

I understand, but at same time you probably know more what the air demands may be than I would having never seen what it all supplies.

Just because the system is at pressure doesn't mean it is drawing rated power, the more air actually being used by items in the plant will increase motor draw. There is a chance this is oversized to allow some additions or even quick recovery as well so even if air demand is at maximum level doesn't mean your compressor is pulling maximum rating.

This all getting at your initial question containing the word "realistically". NEC still requires a conductor able to handle the rating of the motor whether it is fully loaded or not.

Agreed. The plant engineer should have some design criteria. A plant won’t spend $$$ on that big of a compressor without justification. Steel mills generally have a fairly constant demand for air. At least when compared to a general manufacturing plant.

 

[dm9289]

I understand, but at same time you probably know more what the air demands may be than I would having never seen what it all supplies.

Just because the system is at pressure doesn't mean it is drawing rated power, the more air actually being used by items in the plant will increase motor draw. There is a chance this is oversized to allow some additions or even quick recovery as well so even if air demand is at maximum level doesn't mean your compressor is pulling maximum rating.

This all getting at your initial question containing the word "realistically". NEC still requires a conductor able to handle the rating of the motor whether it is fully loaded or not.

I like to go NEC I try my best to follow it. But my guess is they will leave it as is. This is the main compressor then there’s a secondary when it can’t keep up

 

[dm9289]

Agreed. The plant engineer should have some design criteria. A plant won’t spend $$$ on that big of a compressor without justification. Steel mills generally have a fairly constant demand for air. At least when compared to a general manufacturing plant.

Many places have a multi purpose plant engineer and rely on what contractors recommend. Like my plant. I was asked to look it over and gave my opinion. I know we all have made code mistakes but I think when it’s known it should be corrected. My thought was I wonder how much extra capacity is built into the wire or is it right on the dot.

 

[augie47]

Obviously just an opinion but I feel there is probably enough safety factor built into the ampacity that I would be too concerned over any immediate problem. Enhanced insulation damage over time, possible premature component damage due to heat transfer and, maybe most important, a window of opportunity to not warranty any future problems.

 

[dm9289]

Obviously just an opinion but I feel there is probably enough safety factor built into the ampacity that I would be too concerned over any immediate problem. Enhanced insulation damage over time, possible premature component damage due to heat transfer and, maybe most important, a window of opportunity to not warranty any future problems.

Yep It costed around 150k.

 

[retirede]

Many places have a multi purpose plant engineer and rely on what contractors recommend. Like my plant. I was asked to look it over and gave my opinion. I know we all have made code mistakes but I think when it’s known it should be corrected. My thought was I wonder how much extra capacity is built into the wire or is it right on the dot.

My comment was in response to how heavily the compressor might be loaded rather than the electrical aspect. But you make a valid point.

 

[rambojoe]

How many gallons is the tank? Is it feeding multiple daisy chained tanks?

 

[Tulsa Electrician]

By chance you see what the motor name plate says.
293-48= 245*.80= 196
Not disputing the fact the wire size is incorrect for the label on the unit.
Minimum would be what's labeled on the unit. I do not believe you need to add 125%. Since it's a packaged unit with a FLA label.
The minimum would be the 293
A lot of time there a manual that lost minimum wire size for length of circuit. That could also factor into your report.


Just playing with numbers
((200*746)/831)*1.1= 197.49
FYI: 480*1.732= 831
1.1= 90% power factor.

Another item to consider is the wye start. (197.49/1.732)*.577= 65.79
amps than switches to delta run.
FYI: 1/1.732 = .577 or 57.7%

When you get a chance let me know what the motor name plate says.
So it very possible it will run just not NEC compliant with an undersized conductors.

 

[ptonsparky]

Sized adequately for the compressor alone.
What would the additional load be? Cooling? Crankcase heat? Obviously I've never worked on one that sized.