I want to make sure I'm understanding how to derate ampacity correctly.
Given: using 10 AWG wire - 40 ampacity maximum in 3/4" EMT that is mounted .5" above roof surface in 37 Celsius maximum ambient temperature (ASHRAE max temp for Newark, NJ)
1. To start with, 310.15(B)(2)(c) I should add 33 degrees to my already-maximum temperature to arrive at 70 degrees Celsius.
2. Using 310.16 I should derate my ampacity accordingly (.41% for 70 degrees Celsius)
3. Using conduit fill (lets say 6 current-carrying conductors) I should further derate my ampacty by 80%
My final derated ampacity is 40 * 41% * 80% = 13.12 amps.
I guess I'm wondering if I'm doing the temperature part right. It just seems a little redundant to use the extreme max temp from ASHRAE then to derate the temperature even farther to 70 degrees.
This is my maiden voyage in posting on the forum but have appreciated reading many helpful posts in the past.
Thanks in advance
Given: using 10 AWG wire - 40 ampacity maximum in 3/4" EMT that is mounted .5" above roof surface in 37 Celsius maximum ambient temperature (ASHRAE max temp for Newark, NJ)
1. To start with, 310.15(B)(2)(c) I should add 33 degrees to my already-maximum temperature to arrive at 70 degrees Celsius.
2. Using 310.16 I should derate my ampacity accordingly (.41% for 70 degrees Celsius)
3. Using conduit fill (lets say 6 current-carrying conductors) I should further derate my ampacty by 80%
My final derated ampacity is 40 * 41% * 80% = 13.12 amps.
I guess I'm wondering if I'm doing the temperature part right. It just seems a little redundant to use the extreme max temp from ASHRAE then to derate the temperature even farther to 70 degrees.
This is my maiden voyage in posting on the forum but have appreciated reading many helpful posts in the past.
Thanks in advance
