voltage drop and wire size

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staticcontrol

Member
Hello everyone,

First, hope you're all going to have a great summer kick off this weekend.

I was approached to give a ball park estimate of what it would take to provide 200 amps in a warehouse that is 350 feet from main distribution.

I figure to use a 480v primary 208/120 v secondary 75 kva transformer located 350 feet away from main distribution. The Primary breaker size will be 125 amp disconnect. Can someone help size the wire given the distance because of voltage drop?

It's been a while. I came up with 1/0. after derating.

Thank you in advance.

static control
 
M

malachi constant

Senior Member
Location
Minneapolis
At length of 350' and voltage of 480 you should be able to run standard copper wire sizes and be within 3% VD - no upsize required.

If you're using aluminum you are probably OK with a #1, but #1/0 if you want to stay within 3% upsize to a #1/0.

All that said, use the voltage drop calculators you find online - you're better off getting comfortable with one of those than relying on the advice of people you are not familiar with (and who are not familiar with the installation).
 
bob

bob

Senior Member
Location
Alabama
staticcontrol said:
I was approached to give a ball park estimate of what it would take to provide 200 amps in a warehouse that is 350 feet from main distribution.

I figure to use a 480v primary 208/120 v secondary 75 kva transformer located 350 feet away from main distribution. The Primary breaker size will be 125 amp disconnect.
Click to expand...

The Max amperage for a 75 kva is 90 amps. Using the online calculator provided, you only need #3CU. You may want to consider a little larger if you think its needed.
 
S

staticcontrol

Member
Hi bob,

I calculated 90 amps also but I also added 125% as the code states to get breaker size. I assume since it's been a while that the wire size can't be less than the breaker of 125 amps. Any thoughts?

thanks.

static
 
B

brother

Senior Member
Location
"I have learned, in whatsoever STATE I am, therewi
staticcontrol said:
Hello everyone,

First, hope you're all going to have a great summer kick off this weekend.

I was approached to give a ball park estimate of what it would take to provide 200 amps in a warehouse that is 350 feet from main distribution.

I figure to use a 480v primary 208/120 v secondary 75 kva transformer located 350 feet away from main distribution. The Primary breaker size will be 125 amp disconnect. Can someone help size the wire given the distance because of voltage drop?

It's been a while. I came up with 1/0. after derating.

Thank you in advance.

static control
Click to expand...

The formula for Voltage Drop

2kIL/CM single phase
1.73IL/CM 3phase

K=12.9 constant resistance for copper at 75degrees
I= current
L=length
CM=circular mills (found in chpter 9)
 
kwired

kwired

Electron manager
Location
NE Nebraska
staticcontrol said:
Hello everyone,

First, hope you're all going to have a great summer kick off this weekend.

I was approached to give a ball park estimate of what it would take to provide 200 amps in a warehouse that is 350 feet from main distribution.

I figure to use a 480v primary 208/120 v secondary 75 kva transformer located 350 feet away from main distribution. The Primary breaker size will be 125 amp disconnect. Can someone help size the wire given the distance because of voltage drop?

It's been a while. I came up with 1/0. after derating.

Thank you in advance.

static control
Click to expand...

Can you supply the 480 volt and put the transformer at the warehouse?

You will need most of the same items but can use smaller conductors for the 350 foot run, and voltage drop will be less of a problem at 480 volts than it is at 208 volts.
 
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