Voltage Drop?

K

kjroller

Member
Location
Dawson Mn
Occupation
Master electrician
Just out of curiosity what length would you account for voltage drop 1/0 wire 75degree? It is loaded to 146 amps max, 480volts. At about 390' ft I reach the 3% threshold anything under that I would say I'm ok without having to upsize. Let me know what you get or if you have any input on this!
 
This sounds like a study question, tell us what you think and how you came to your answer and someone can verify or help you
 
3% is arbitrary. There is no one answer to this in real life. How much is too much is subject whether there is a contractual obligation, a energy code requirement, manufacturer specs/instructions/recommendations, and your professional judgement.
 
I plugged it into the Southwire voltage drop app that is what I got it is just a question not for a test but I was told by a company I need 2/0 after 200 feet I do not believe this to be correct and was seeing what your thoughts are.
 
Also I don't believe this is arbitrary it is written in the code 3% for branch circuits and 5% for feeders and branch circuits. Article 210.19 (Informational note)
 
kjroller said:
Also I don't believe this is arbitrary it is written in the code 3% for branch circuits and 5% for feeders and branch circuits. Article 210.19 (Informational note)
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Informational notes are not binding. And those numbers are still basically arbitrary 'rules of thumb' that may be more or less than a given situation actually needs if you were to dig into it. Following that informational note is arguably perfectly fine professional judgment most of the time; occasionally it might be either inadequate or overkill.
 
kjroller said:
Also I don't believe this is arbitrary it is written in the code 3% for branch circuits and 5% for feeders and branch circuits. Article 210.19 (Informational note)
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No not the NEC its in a different code, I don't know what its called, its the same code that says where you need occupancy and vacancy sensors, they just started enforcing the VD part of it a few years back.
 
Well I guess it is only a recommendation since 90.5 says informational notes are not mandatory rules you learn something new every day that being said still probably a good idea to follow the recommendation if you want your equipment to be efficient.
 
So in Minnesota it is required buy energy conservation code? So is this adopted by all MN municipalities or who enforces this?
 
kjroller said:
Well I guess it is only a recommendation since 90.5 says informational notes are not mandatory rules you learn something new every day that being said still probably a good idea to follow the recommendation if you want your equipment to be efficient.
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Depends what you mean by efficient. With old incandescent bulbs you just get less light, but also less consumption and therefore lower bills. With newer LED drivers that's not likely to be the case. Some motors are designed to expect a certain amount of voltage drop and may not actually work more efficiently with higher voltage at the terminals.
 
jaggedben said:
Depends what you mean by efficient. With old incandescent bulbs you just get less light, but also less consumption and therefore lower bills. With newer LED drivers that's not likely to be the case. Some motors are designed to expect a certain amount of voltage drop and may not actually work more efficiently with higher voltage at the terminals.
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Like running a 100hp compressor motor probably want to adjust for that most mine are squirrel cage non energy efficent
 
kjroller said:
Like running a 100hp compressor motor probably want to adjust for that most mine are squirrel cage non energy efficent
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Depending on the type of compressor and starting method, you might have problems starting the unit. That’s a bigger consideration than a (relatively) small voltage drop at full load.
 
kjroller said:
Like running a 100hp compressor motor probably want to adjust for that most mine are squirrel cage
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Inductive motor loads cause current to rise with voltage drop.

The Southwire Voltage-Drop app can adjust power factor, but fails to differentiate inductive loads for current rise.

NEC Tbl 430.250 notes * adjustments for 0.8 or 0.9 power factors

NEC Tbl 430.22(E) requires up to 200% of nameplate current rating for varying duty (perhaps compressors)
kjroller said:
told by a company I need 2/0 after 200 feet
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Engineering supervision requires a Stamped PE letter, if you're not trained in NEC adjustments from section 430.
 
kjroller said:
Just out of curiosity what length would you account for voltage drop 1/0 wire 75degree? It is loaded to 146 amps max, 480volts. At about 390' ft I reach the 3% threshold anything under that I would say I'm ok without having to upsize. Let me know what you get or if you have any input on this
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I did the math and the 1/0 allows a 3% VD for branch circuit. Will check if 3 phase changes result
 
kjroller said:
So in Minnesota it is required buy energy conservation code? So is this adopted by all MN municipalities or who enforces this?
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I think of the energy code like a huge pothole on the highway, we can be cruising along just fine then all of a sudden its bam we slam into it.
Then the whole project grinds to a halt while I have to fix the flat (make a lighting compliance form, figure out occupancy / vacancy sensors daylight lighting controls, transformer efficiency, motor efficiency, voltage drop ... ) and then with some unexpected expense the job gets going again.
 
pipe_bender said:
No not the NEC its in a different code, I don't know what its called, its the same code that says where you need occupancy and vacancy sensors, they just started enforcing the VD part of it a few years back.
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Yes, there are enforceable voltage drop rules in the energy codes that the feds have requires the states to adopt. Not all states enforce their adopted energy codes.
 
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