piston
Member
- Location
- Concord, NH
Hello I am new to the forum. I have a question about three phase. I am a student also so i will show my work and then ask specific questions at the bottom.
The problem i am working on:
Given data for the problem:
-IMC installed in a room with ambient temperature of 110 F
-thhn/thwn conductors are used
-growth allowance of the computed load is 10%
-the power factor will be maintained at 90% or higher
-conductor length is 180 feet
-voltage drop at max load shall not exceed 2%
Continuous load=20,000 va
Non Continuous load/receptacles=12,000 va
highest motor= 8,000 va
other motor= 16,000 va
nonlinear= 20,000 va
balanced= 24,000 va
Non continuos load
Non continuous/receptacles = "12,000" va
largest motor = "8,000" va
25% of the largest motor = "2,000" va
Other motor = "16,000" va
"38,000" va non-continuous subtotal
Continuous load
Continues load = "20,000" va
Continues load + 25% = "5,000" va
"25,000" va continuous subtotal
non-continuous subtotal = "38,000" va
continuous subtotal = "25,000" va
subtotal = "63,000" va
Plus 10% growth = "6,300" va
TOTAL VA = "69,300" va
Convert VA to I
"69,300/(208V*1.732)" = 192 amps
Conductor chosen for use
THWN at 75? C = 300 kcmil rated at 285 amps
Conductor adjustment
I * conductor count factor = 285a * 80% 228 amps
Conductor correction factor
I * temperature factor = 228a * 95% 217 amps
This would be a 250 kcmil thwn
Neutral Conductor sizing
125% of the Total load = Maximum neutral current in VA
192amps * 1.25 = 240 amps
Adjustment/Correction of the neutral 182.4 amps
Questions:
Did I calculate the ungrounded conductors correctly?
Did I calculate the grounded (neutral0 correctly)?
I have been working on this for hours on end each day and the code is very vague on the neutral conductor calculations or even 3 phase (in my opinion). But I am a beginner so what do i know. :slaphead:
The problem i am working on:
Given data for the problem:
-IMC installed in a room with ambient temperature of 110 F
-thhn/thwn conductors are used
-growth allowance of the computed load is 10%
-the power factor will be maintained at 90% or higher
-conductor length is 180 feet
-voltage drop at max load shall not exceed 2%
Continuous load=20,000 va
Non Continuous load/receptacles=12,000 va
highest motor= 8,000 va
other motor= 16,000 va
nonlinear= 20,000 va
balanced= 24,000 va
Non continuos load
Non continuous/receptacles = "12,000" va
largest motor = "8,000" va
25% of the largest motor = "2,000" va
Other motor = "16,000" va
"38,000" va non-continuous subtotal
Continuous load
Continues load = "20,000" va
Continues load + 25% = "5,000" va
"25,000" va continuous subtotal
non-continuous subtotal = "38,000" va
continuous subtotal = "25,000" va
subtotal = "63,000" va
Plus 10% growth = "6,300" va
TOTAL VA = "69,300" va
Convert VA to I
"69,300/(208V*1.732)" = 192 amps
Conductor chosen for use
THWN at 75? C = 300 kcmil rated at 285 amps
Conductor adjustment
I * conductor count factor = 285a * 80% 228 amps
Conductor correction factor
I * temperature factor = 228a * 95% 217 amps
This would be a 250 kcmil thwn
Neutral Conductor sizing
125% of the Total load = Maximum neutral current in VA
192amps * 1.25 = 240 amps
Adjustment/Correction of the neutral 182.4 amps
Questions:
Did I calculate the ungrounded conductors correctly?
Did I calculate the grounded (neutral0 correctly)?
I have been working on this for hours on end each day and the code is very vague on the neutral conductor calculations or even 3 phase (in my opinion). But I am a beginner so what do i know. :slaphead: