Conductor Temperature Rating with 25' Tap rule

steve holt

Member
Location
Hawaii
Is it allowable to use the 90 degree rating instead of 75, when calculating the conductor size using the 25' tap rule? One end is terminated directly to busing, and the other to a breaker.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Engineer
There are few, if any, breakers less than 600v with 90° ratings so you would have to terminate based on 100.14, normally 75°
I belive that UL standards for molded case breakers and fusible switches do not allow 90C at the terminals. 100% rated equipment requires 90C conductors sized at 75C.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
I agree you won't find a standard circuit breaker with 90° C terminals so the tap conductor ampacity is based on the 75° C conductor ampacity.
 
Top