# Differnece between Nec Table 310.15(B)(16) vs 310.15(B)(2)(1)



## kduff70 (Feb 28, 2015)

I was going over Ncees sample power problem 104 and the thing that becomes a sticking point with me is making sure I use the correct ampacities table from the NEC. So can someone explain to me if my approach to this problem is ok? Now every time I go over this problem I tend to use table 310(B)(16) because it in the general wring used for motors and the problem state its single phase where if I tried to use table for annex B it would not be correct because it not require by NFPA and also these table have adjustment factor in them for more than 3 current carrying conductors that would not work for the problem?


----------



## zm83 (Feb 28, 2015)

If you look at annex b it states that "This informative annex is not a part of the requirements of this NFPA document but is included for informational purposes only."

That tells me your initial thought is correct. I get to where sometimes I overthink the NEC. When I did that problem at first I got it wrong because I used 110% but further looking into the code it says for feeders feeding motors and additional loads 125%


----------



## Kovz (Mar 2, 2015)

This problem involves multiple tables and articles that the solution does not list.

First, the 10HP single phase motor has it's FLA found on Table 430.248. Listed as 50A.

Next, the heater is I = 1kw/240 = 4.17A

Next see article 430.24 - Several motors or a motor and other loads: Take 125% of the motor = 62.5A. Then take 100% of the heater because it is a non-continuous load = 4.17. Add the two loads together to get 66.67A.

Then use Table 310.15(B)(16) under 75*C, Copper, THWN. The table shows #6 is only good for 65A, so that would not be good enough for a 66.67A load. So the next larger size is #4, which is good up to 85A. So the answer is C, 4 AWG.


----------

