ohmboyz
Member
- Location
- Millbrae CA, San Mateo
I am coaching one of my students who is preparing to sit for the California certification. She is using Tom and Tim Henry's 2014 exam preparation text. One of the chapter 2 (don't have it in front of me, but I believe it was this chapter) questions is what is the allowable ampacity for 4, 4/0 THWN copper conductors with an ambient temperature of 45 celsius. No terminal temperature rating is given. I told her that she had to use the 60 degree column as a starting point, even though THWN is listed in the 75 degree column. Accordingly, the calculation I suggested she use was (195)(0.80)(0.82). The result would then be 127.92, or 128. When we looked up the answer, the result was 150.88---151 amps. Clearly, the Henrys' starting point was 230 amps from the 75 degree column. In the absence of any information on terminal temperature rating, is it not true that one must proceed with the 60 degree column?