Sizing conductors and ground for 300hp motors

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Fella

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Hi there, I've searched the forum for years as I've needed but just joined today. I've got a few runs of wire i would like some input on sizing. I'm self taught so anxious to learn any time i can.

Run 1
300 hp motor, according to my chart it should be 361 fla, but the manufacturer book calls for 458. Equipment is still in asia.

180 feet run. Equipment will run at roughly 60% load for 50 out of 60 minutes for 8 hours a day.

I'm coming up with 2 runs out 4/0 copper with #1 ground for each run calculated at 75 degrees.

Run 2
300 hp motor, same fla discrepancy.
280 foot run
This unit will run at 90% roughly 3 to 5 hours a day. I'm showing 4/0 is still okay but borderline so i thought id do 2 runs of 250 mcm to be safe, because of the fla discepancy and continuous load.

What are your thoughts and reasoning behind it?
 
infinity said:
Which number are you using in your calculation?
Click to expand...
So either number works on that shorter run, they both give me that wire.

I'm trying to figure out now why the discrepancy. I think it's a voltage difference bc the motors/equipment are designed for europe. The book lists everything is kw and kva. Or maybe they are talking about overcurrent protection and used the wrong words. It's in very bad English

To keep this simple, let's discuss it at 361. I'm mainly looking for the principle a knowledgeable electrician uses so i can apply it to any job i do.

If i know the principle, i can change it if that 458 turns out to be correct.
 
So i basically looked at the ampacity chart for wire size, did a voltage drop check using the southwire calculator to see if i need to correct for distance, and i adjusted the longer run for continious load per the nec, but not the short since it's not continious and not close to fla anyway so the 4/0 still was enough.

Then i pulled the ground conductor sizing chart for equipment feeders.
 
The NEC tables are usually quite conservative. That the manufacturer's number is so much higher should be a red flag to look for something unexpected such as an uncommon drive voltage.

At 180 feet and 460A 3 phase 480V, 2x 4/0 Cu gives a voltage drop of less than 1%.

Why do you say this is marginal?

Jon
 
I would start with actual nameplate data, not assumptions. How can you do sizing if you don’t know the frequency, speed or voltage that the motors are rated for?
 
Step 1 select conductors based upon the required ampacity.

Step 2 calculate voltage drop given the selected conductors and length of run

Step 3 increase conductor size if needed to get acceptable voltage drop.

A 3% or less voltage drop is generally acceptable, but the actual value you can tolerate is application specific.

Jon
 
winnie said:
The NEC tables are usually quite conservative. That the manufacturer's number is so much higher should be a red flag to look for something unexpected such as an uncommon drive voltage.

At 180 feet and 460A 3 phase 480V, 2x 4/0 Cu gives a voltage drop of less than 1%.

Why do you say this is marginal?

Jon
Click to expand...
That one was fine, it was the longer run that i was coming up with it being right in the line. And that's the one that they tell me will be at 90% of fla so i want to make sure it's right. What are your thoughts on that longer run?

Is my ground sizing correct, I'm using 250,122
 
MTW said:
I would start with actual nameplate data, not assumptions. How can you do sizing if you don’t know the frequency, speed or voltage that the motors are rated for?
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I'm working on that, it's very difficult to get info out of them so it might be a week. I'm more concerned with making sure the principles I'm using are correct and then i can size anything.

I spent my 20s managing a large service company with 30 to 50 employees. I learned by google, i have no formal training and have only been in the field with my own company a few years so that's why i was wanting help from the experts.
 
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winnie said:
Step 1 select conductors based upon the required ampacity.

Step 2 calculate voltage drop given the selected conductors and length of run

Step 3 increase conductor size if needed to get acceptable voltage drop.

A 3% or less voltage drop is generally acceptable, but the actual value you can tolerate is application specific.

Jon
Click to expand...
Thank you, sounds like I'm doing it right. I was just a little nervous. We've got multiple of each run so we're talking about a lot of wire. And conduit is overhead so it's very time consuming to run. I try to keep my repurchase as the guy that always does thing correctly but i do every trade basically so sometimes i just flat out don't know if I'm right.
 
zbang said:
Unfortunately, that's a a bit of a yellow flag-
Is the equipment UL/NRTL listed?
Does it run on 60Hz and a common US voltage? (Is it even made for the US market?)
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Yes its a very popular company, there's like 40 of them in my state that i know of. Not sure on ul.

Its all 480v 60htz. I'm in big ag, its not unheard of for a few companies to use metric motors bc holland is the cornerstone of our industry. 80% of my customers are from there and a lot of companies were started there.

I used to be a dealer for the largest or second largest dairy equipment manufacturer in the world. A lot of our data and some parts were metric with sae notations in the book.
 
Fella said:
That one was fine, it was the longer run that i was coming up with it being right in the line. And that's the one that they tell me will be at 90% of fla so i want to make sure it's right. What are your thoughts on that longer run?

Is my ground sizing correct, I'm using 250,122
Click to expand...

Using the Southwire voltage drop calculator, with a distance of 280 feet, 480V three phase, 2x 4/0 Cu conductors, 460A, I get a voltage drop which is 1.4%, generally acceptable.

What OCPD are you using? #1 Cu EGC is usable for a 600A breaker.

-Jon
 
winnie said:
Using the Southwire voltage drop calculator, with a distance of 280 feet, 480V three phase, 2x 4/0 Cu conductors, 460A, I get a voltage drop which is 1.4%, generally acceptable.

What OCPD are you using? #1 Cu EGC is usable for a 600A breaker.

-Jon
Click to expand...
That longer run unit is continuous use so correct me if I'm wrong.

I took 90% of fla, x 1.25 and used that number for the voltage drop. 90% is what the equipment company tells me that unit will run at typically.

From what im understanding on continous use of 3 hours or more, you allow for 25% over the continious load, plus the value of the non continious load (0 in this case) which increases the wire size to allow for thermal effects on the wire. Is that incorrect?

Is i use that 25% over the running load, i exceed the ampacity of 4/0x2

These will be ran with a vsd and fed by a 600a breaker
 
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Fella said:
That longer run unit is continuous use so correct me if I'm wrong.

I took 90% of fla, x 1.25 and used that number for the voltage drop. 90% is what the equipment company tells me that unit will run at typically.

From what im understanding on continous use of 3 hours or more, you allow for 25% over the continious load, plus the value of the non continious load (0 in this case) which increases the wire size to allow for thermal effects on the wire. Is that incorrect?

Is i use that 25% over the running load, i exceed the ampacity of 4/0x2

These will be ran with a vsd and fed by a 600a breaker
Click to expand...
If your using a VSD, you should be sizing your circuits based on the drive input requirements, not the motor data, they will be different.
 
Fella said:
That longer run unit is continuous use so correct me if I'm wrong.

I took 90% of fla, x 1.25 and used that number for the voltage drop. 90% is what the equipment company tells me that unit will run at typically.

From what im understanding on continous use of 3 hours or more, you allow for 25% over the continious load, plus the value of the non continious load (0 in this case) which increases the wire size to allow for thermal effects on the wire. Is that incorrect?

Is i use that 25% over the running load, i exceed the ampacity of 4/0x2

These will be ran with a vsd and fed by a 600a breaker
Click to expand...
For the motor the conductors are sized at 125% of the current value in T430.250. Variable drives conductors are sized at 125% of the drive input current.

In post #2 I asked which of the current numbers you're using for Run 1. You didn't respond. If you use 458 amps then parallel #4/0's are too small.
 
Fella said:
So either number works on that shorter run, they both give me that wire.

I'm trying to figure out now why the discrepancy. I think it's a voltage difference bc the motors/equipment are designed for europe. The book lists everything is kw and kva. Or maybe they are talking about overcurrent protection and used the wrong words. It's in very bad English

To keep this simple, let's discuss it at 361. I'm mainly looking for the principle a knowledgeable electrician uses so i can apply it to any job i do.

If i know the principle, i can change it if that 458 turns out to be correct.
Click to expand...
If the motors are designed for Europe they would likely be intended for 50Hz, 400V. That that could be a problem for you.
 
Actually, a 400V 50Hz motor works fine here with 480V 60Hz, because the V/Hz ratio is the same. But it will spin 20% faster, which CAN be a serious problem for centrifugal pumps and fans but with there being VFDs involved, that issue goes away.

INPUT conductors to the VFD must be sized to the INPUT current of the VFD x 1.25. OUTPUT conductors are sized per the standard motor conductor sizing rules: 125% of the NEC table FLC value for the HP, or the nameplate FLA if it is higher than the table values (ie high pole count motors).

iI it were me, I would not be cutting wire until I can see the actual motor nameplates. Minor errors can be really expensive at these sizes.
 
Jraef said:
Actually, a 400V 50Hz motor works fine here with 480V 60Hz, because the V/Hz ratio is the same. But it will spin 20% faster, which CAN be a serious problem for centrifugal pumps and fans but with there being VFDs involved, that issue goes away.

INPUT conductors to the VFD must be sized to the INPUT current of the VFD x 1.25. OUTPUT conductors are sized per the standard motor conductor sizing rules: 125% of the NEC table FLC value for the HP, or the nameplate FLA if it is higher than the table values (ie high pole count motors).

iI it were me, I would not be cutting wire until I can see the actual motor nameplates. Minor errors can be really expensive at these sizes.
Click to expand...
That's what I'm trying to minimize. Trying to meet a deadline and not waste wire. I'm not concerned with the principle of how to size it correctly. If they give me different numbers in a week when i finally get an answer, i can refigurec it if i know the principles.

I have 0 interest in getting an answer on wire sizing for this job from anyone. I have 100% interest in seeing the correct thought process so i can size any job that i come across. If that makes sense. I'm trying to learn how to fish, not get handed a can of fish.
 
infinity said:
For the motor the conductors are sized at 125% of the current value in T430.250. Variable drives conductors are sized at 125% of the drive input current.

In post #2 I asked which of the current numbers you're using for Run 1. You didn't respond. If you use 458 amps then parallel #4/0's are too small.
Click to expand...
I think you missed it, i said for this discussion, let's figure it at 361. I'm more concerned with making sure I'm taking into account all factors and see the thought process so i can do these calculations on my own in the future. If holland comes back with 458 fla then I'll refigure it.

I size a lot of jobs and I've never had an issue but usually they are smaller and wire cost is much less.
 
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