mshields
Senior Member
- Location
- Boston, MA
Table 310.15B2a shows derating factors for ambient temperatures lower than 30deg C. it's sister on the next page, i.e. Table 310.15 B 2 b shows derating factors for ambient temperatures other than 40 deg C.
Obviously the first table is for when it is colder than the acceptable range 30 to 40 deg C. One would expect that the second table is for hotter than 40 degrees C hence covering the whole range. But whereas the first table only covers the lower than 30deg C, the second table covers the entire range of temperatures starting with 10 or less and going all the way up to 225deg C.
So for the colder temperatures, which table does one use to determine the derating factor? I would think that the answer is that you always use the first table for cold area's but what then is the purpose of having the cold temperatures covered in the second table as well?
Obviously the first table is for when it is colder than the acceptable range 30 to 40 deg C. One would expect that the second table is for hotter than 40 degrees C hence covering the whole range. But whereas the first table only covers the lower than 30deg C, the second table covers the entire range of temperatures starting with 10 or less and going all the way up to 225deg C.
So for the colder temperatures, which table does one use to determine the derating factor? I would think that the answer is that you always use the first table for cold area's but what then is the purpose of having the cold temperatures covered in the second table as well?