sizing conductors
- Thread starter JdoubleU
- Start date
- Status
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I agree it is correct however the final ampacity after derating cannot be larger then the 75C column
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Don't you mean that the final conductor ampacity after derating must greater than or equal to the 75? C rating?
No.
The final conductor ampaciity is the lesser of the derated value or the 75?C column's value.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Not exactly what Dennis said. Your conductor ampacity can exceed the 75? C ampacity after derating. Sounds like he's not talking about the conductor.
I know it's not exactly what Dennis said, but it amounts to the same. And no, the way I stated it, my conductor ampacity cannot exceed the 75?C column's ampacity value. Dennis is talking about the conductor.
Let's use a 1/0 copper THHN for example. The table values are 150 and 170. If the derated ampacity is 140, then 140 < 150, so the in-use ampacity is 140. If the derated ampacity is 160, then 160 > 150, so the in-use ampacity is 150.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Well I am glad we got that cleared up. 
north star
Senior Member
- Location
- inside Area 51
: - :
Essentially,
The terminal rating governs and the conductors cannot
exceed the [ max. ] rating of the terminal.....The 90
degree column can be used to meet the [ max. ] rating
of the terminal.....Derate the conductors down to the
terminal rating.
: - :
Essentially,
The terminal rating governs and the conductors cannot
exceed the [ max. ] rating of the terminal.....The 90
degree column can be used to meet the [ max. ] rating
of the terminal.....Derate the conductors down to the
terminal rating.
: - :
- Status