Parallel feeder size for voltage drop is questionable

Status
Not open for further replies.
I

Isaiah

Senior Member
Location
Baton Rouge
Occupation
Electrical Inspector
They designed 2-3/C 1000 kCMIL/phase to a 75 kVA dry type transformer (480-120/208V) about 900’ away. Then they tapped off on the primary side with 350kCMIL and tan to another 75kVA transformer 450 feet from the tap.
Both XFMR are loaded to about 80%.
I used an online calculator and it shows 1-3/C conductor 1000kCMIL would be sufficient with the 350kCMIL to the second XFMR. I’m just wondering why they’d to run such large parallel conductors to such a small load - am I missing something here? Can somebody back check the calculation?


Sent from my iPhone using Tapatalk
 
Which online calculator were you using?
I got 2/0, two sets, 3-conductor Cu for 900 feet with total amps of 180.4 (two 75 kVA transformers @ 480V three-phase. The allowed voltage drop was 3% for the feeder.
The 450 feet tapped-off line should be a 2-set X #3, 3-conductor Cu, or a 1-set X 1/0, 3-conductor Cu, allowing a 2% voltage drop with 90.4A. (total VD = 5%)
There is no problem with stringing more than the required size of conductors. As long as you have the money to buy those and besides, you never mentioned whether the owner intends to expand in the next few years or so. I have had a project where the client opted to skimp on the materials cost and asked for a quote in just three years when he added more loads. A total revamp was required costing 3 times more than if the installation was future-proofed the first time!
 
topgone said:
Which online calculator were you using?
I got 2/0, two sets, 3-conductor Cu for 900 feet with total amps of 180.4 (two 75 kVA transformers @ 480V three-phase. The allowed voltage drop was 3% for the feeder.
The 450 feet tapped-off line should be a 2-set X #3, 3-conductor Cu, or a 1-set X 1/0, 3-conductor Cu, allowing a 2% voltage drop with 90.4A. (total VD = 5%)
There is no problem with stringing more than the required size of conductors. As long as you have the money to buy those and besides, you never mentioned whether the owner intends to expand in the next few years or so. I have had a project where the client opted to skimp on the materials cost and asked for a quote in just three years when he added more loads. A total revamp was required costing 3 times more than if the installation was future-proofed the first time!
Click to expand...

thanks so much topgone!
There’s no chance for expansion here, it’s ‘fixed’ and besides it’s temp only - “calculator.net” voltage drop calculator


Sent from my iPhone using Tapatalk
 
Status
Not open for further replies.
Top