4-006(1) says: "Where equipment is marked with a maximum conductor termination temperature, the maximum allowable ampacity of the conductor shall be based on the corresponding temperature column from Tables 1, 2 ,3, or 4." Does this refer only to the ampacity inside the enclosure containing the equipment or does it mean that derating is based on the lower temperature? For example, a conduit might contain more than 3 conductors or it might pass through a high ambient area.
Sorry, I didn't think that through. If 4-006 applied outside the enclosure, the solution could be to put a box between the enclosure and the high ambient area and to use the same conductors on both sides of the box. Where did the "delete post" button go?
Nope. In the 2012 code section 4 has completely changed with regard to ampacity and the Canadian code has finally removed a standing error in calculating wire ampacity. All the product tests of temperature rated devices Like circuit brekers is based on 60 or 75 degrees but we have been applying ampacity of the 90 degree colums to all connections. So the rule may be affected by ambient and there are tables to derate for temperature or number of current carrying wires. So a device like a circuit breaker creates some heat and the tests to calibrate the breaker are based on 75 degree wire. So if you terminate a wire on a breaker the ampacity must be based on the 75 degree columns of tables 1 to 4 and not the 90 degree column we have used for years.
I understand that the wire on the breaker must be sized to limit potential temperature at the terminal to the rating of the terminal. The question is whether that heat will travel 50 feet down the conductor and increase the conductor temperature at the other end.
TWH Lowering of standards? yes I suppose it is but what if the base standard was the only one in the world that set it so high? Second point is the Canadian code has ignored the temperature requirments for as long as I can remember or 1976 which ever came first when I bought my first code book. SO we had overly conservative ampacity tables that did compensate somewhat for the terminal issue. One important use of 90 degree wire is at luminaires which usually require at least 90 degree wire but now the breaker end can only be ampacity from the 75 degree column. I guess since i voted to accept the rule changes I am happy to take 1/36th of the blame. At the outset it was the intention of the uniformity committee to get the NEC to use our method but in the end we did not deal with the terminal issue.