voltage drop, using parrellel conductors

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robby robinson

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I have a job, where we have a 2000 amp feeder from one building to another, we are planning on using 6 sets of 750 mcm aluminum, the feeder is 300 foot long and the computed load on the feeder is 1500 amps. from where we terminate the feeder, we then have a sub feeder to a meter bank, 200 feet away, the feeder will be a 600 amp, using 2 sets of 350mcm copper, the computed load on this feeder is 480 amp. from the meter bank to the furthest condo unit is 150 feet, we are using 3/0 aluminum type mc cable to feed the unit, the computed load on each condo unit is 100 amp.

On the 200 amp feeder, we may use a MC Stabiloy cable, rather then metal conduit.
 
bdarnell

bdarnell

Senior Member
Location
Indianapolis, IN
Occupation
Retired Engineer
Here's the formula, if that is what you are seeking:

VD = 1.732 x K x I x D / CM

K for AL is 21.2

I did the first segment for you and it's a 3.7 volt drop. See if you get the same thing.

And yes, you have to do each segment seperately.
 
gngren

gngren

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Location
Metro Tri-State area PA,MD,VA,WV,DC
Additional question?

Additional question?

Robby Robinson said:
I have a job, where we have a 2000 amp feeder from one building to another, we are planning on using 6 sets of 750 mcm aluminum, the feeder is 300 foot long and the computed load on the feeder is 1500 amps. from where we terminate the feeder, we then have a sub feeder to a meter bank, 200 feet away, the feeder will be a 600 amp, using 2 sets of 350mcm copper, the computed load on this feeder is 480 amp. from the meter bank to the furthest condo unit is 150 feet, we are using 3/0 aluminum type mc cable to feed the unit, the computed load on each condo unit is 100 amp.

On the 200 amp feeder, we may use a MC Stabiloy cable, rather then metal conduit.
Click to expand...

I was asked by Robby to see if we could get a confirmation on wire sizes we propose to use with the following information. We would like to compare to what we calculated the voltage drop to be, and if we could get some advise as to if the wire sizes that we think we can use would be correct or need to be changed.

1) The feeder from the main tower to the north warehouse building is now 260? long, we want to use 6 sets of 750 mcm al, as the feeder, the voltage is 120/208, 3 phase, the feeder is to be fused at 2000 amp, the calculated load on that feeder is 1500 amp

2) The feeder in the north warehouse distribution area to the meter bank is now 150? it is fused at 600 amp, it is a 120/208 volt, 3 phase feeder with a calculated load of 480 amp, we plan to use two sets of 400 mcm al., as the feeder, of course we could increase the size if necessary.

3) From the meter bank to the furthest condo unit is now 125?, the feeder is a 120/208 volt, single phase feeder, we plan to use 2/0 al. in cable as the feeder, if necessary we could increase the size of this feeder.

4) Now the total distance from the service in the main tower to the last condo unit is 535?.

Any help in this matter would be appreciated.
 
eric stromberg

eric stromberg

Senior Member
Location
Texas
At the outset, this sounds like it is entirely too far for a 120 Volt circuit.
You should consider the use of transformers.
If i read this correctly, the source of power is at a warehouse?
Is 480 Volts available at the warehouse location? If not, you might consider seeing what it would take to get 480 there. The savings in cable might pay for some of the other work and you'd have a better, more efficient system.

NEC table 9 has all you the information you need to calculate voltage drops. At the end of the table, in the notes, is the formula:
Z = Rcos(theta) + Xsin(theta)
where cos(theta) = the power factor of the load.

E=I*Z
Voltage drop = (current)*(cable impedance)

Understand that the impedance values given are phase to neutral, and all the currents we ever use in the electrical world are also phase to neutral. This gives a voltage drop of phase to neutral. If you want to compare this to a three phase system voltage (line to line), you'll have to multiply the voltage drop by sqrt(3).

Eric
 
bob

bob

Senior Member
Location
Alabama
Asumption: 1500 amps includes the 480 amps condo load.



120/208 ___1500 a___ 117 v ___480 a ____115.6 v ___100a___114 v
start --------6# 750------2.7%-----2 #400-------3.9%-----1 #2/0----5.5%
----------------------------- VD--------------------------VD-------------------VD

gngren
2) The feeder in the north warehouse distribution area to the meter bank is now 150? it is fused at 600 amp, it is a 120/208 volt, 3 phase feeder with a calculated load of 480 amp, we plan to use two sets of 400 mcm al., as the feeder, of course we could increase the size if necessary.
Click to expand...

The origional post said 350 copper.
 
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