pedorrero79
Member
Hello all,
I need to get my head straight on something and I'm hoping you guys can help. I'm taking a NEC course at a local tech school and we were discussing sizing conductors. In the class, we've discussed two methods for sizing conductors.
1. Table 310.16 (the method I use at work)
2. Using the equations CMIL=(2*k*I*L)/Vd (for 1-phase) or CMIL=(1.732*k*I*L)/Vd (for 3-phase) and referencing Table 8 in the NEC
where k=12.9, I=current in the system, L=length of the circuit, and Vd=voltage drop (using 3% for this example)
During class last night, he gave us the following example (paraphrased):
"A 208V/3-phase system has a 120kVA load. The length of the circuit is 100'. What size conductors should be used?"
Immediately, I considered using the equation he had given us (which, BTW, I don't quite understand where he got that, but that's another topic for another day...). Knowing that I have to solve for I, I calculated it out and came up with I=~333A. Plugging this into the equation yields a wire size of 2/0AWG. However, according to T310.16, 2/0 is only rated for 175A (using the 75 degree column) and I'd have to use 400MCM conductors.
The confirmation I'm looking for is "am I correct in thinking that I should be using T310.16 instead of the 'calculated' wire size?"
Any and all help is appreciated. :thumbsup:
Thanks in advance.
-P
I need to get my head straight on something and I'm hoping you guys can help. I'm taking a NEC course at a local tech school and we were discussing sizing conductors. In the class, we've discussed two methods for sizing conductors.
1. Table 310.16 (the method I use at work)
2. Using the equations CMIL=(2*k*I*L)/Vd (for 1-phase) or CMIL=(1.732*k*I*L)/Vd (for 3-phase) and referencing Table 8 in the NEC
where k=12.9, I=current in the system, L=length of the circuit, and Vd=voltage drop (using 3% for this example)
During class last night, he gave us the following example (paraphrased):
"A 208V/3-phase system has a 120kVA load. The length of the circuit is 100'. What size conductors should be used?"
Immediately, I considered using the equation he had given us (which, BTW, I don't quite understand where he got that, but that's another topic for another day...). Knowing that I have to solve for I, I calculated it out and came up with I=~333A. Plugging this into the equation yields a wire size of 2/0AWG. However, according to T310.16, 2/0 is only rated for 175A (using the 75 degree column) and I'd have to use 400MCM conductors.
The confirmation I'm looking for is "am I correct in thinking that I should be using T310.16 instead of the 'calculated' wire size?"
Any and all help is appreciated. :thumbsup:
Thanks in advance.
-P
