# Thread: Sizing the conductor for a Chiller

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## Sizing the conductor for a Chiller

Hi, my name is Ammar and this is my first post in this awesome forum,

I already know that to size a conductor for an A.C. equipment i should have the following (as per 440.4.(B)):
1. The minimum Circuit ampacity.
2. The maximum Over current Protection.

in my case I already have these values (678.48 A and 950 A respectively).

now, when I go to table 310.15.B.2.1 NEC 2011, I can't find the value that I am looking for in the 60C column, the last value in the 60 c Column is 448A!!
my question is:
1. how do I size my cable for the chiller specifically?
2. how do I size cables for high currents in general?

Regards,
Ammar

2. Most of us don't have the P.E. after our names so we don't get to use the "B" Tables as they are for engineer specs.
In the every day world we would use 310.15(b)(16).
For high currents, the conductors are often paralleled so for that current it would likely be supplied by (2) 500 kcmils or (3) 4/0s.
As you know, it gets a bit more complicated due to derating if you parallel in the same raceway or i you have high ambient such as rooftop temperatures.

I would assume, under engineered supervision, you could follow the same plan in the "B" Tables. Keep, in mind, installation of cables larger than 500 has a degree of difficulty that often leads one to paralleleing
Last edited by augie47; 02-09-19 at 10:44 AM.

3. Originally Posted by AmmarAbdou
Hi, my name is Ammar and this is my first post in this awesome forum,

I already know that to size a conductor for an A.C. equipment i should have the following (as per 440.4.(B)):
1. The minimum Circuit ampacity.
2. The maximum Over current Protection.

in my case I already have these values (678.48 A and 950 A respectively).

now, when I go to table 310.15.B.2.1 NEC 2011, I can't find the value that I am looking for in the 60C column, the last value in the 60 c Column is 448A!!
my question is:
1. how do I size my cable for the chiller specifically?
2. how do I size cables for high currents in general?

Regards,
Ammar
I can't find you reference to the 2011 NEC.

But using standard Table 310.15(B) (16); 75 deg C column, without any adjustments or considerations for installation method you could use 2 parallel sets of 400KCMIL (670A)

4. Originally Posted by kingpb
I can't find you reference to the 2011 NEC.

But using standard Table 310.15(B) (16); 75 deg C column, without any adjustments or considerations for installation method you could use 2 parallel sets of 400KCMIL (670A)
One small problem: His MCA is 678

5. Originally Posted by augie47
One small problem: His MCA is 678
oops, my dyslexia thought it said 668A.

6. Originally Posted by kingpb
I can't find you reference to the 2011 NEC.
Look in Annexes.

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