Do you have to size all wire in a house out of the 60c degree column in 310.16 of the nec including the ser cabletype xhhw for the range?

Answer 1

You don't necessarily have to size all wire from the 60c column. However there are three main reasons to do so: 1) The circuit breaker is marked "60/75c" and installed with other breakers in a panelboard 2) Your appliance is not specifically marked for a higher rating (either 75c or 90c) 3) Any part of your circuit is rated at 60c (explained below) In order to use a rating, whether it be 60c, 75c, or 90c, the enclosure, circuit breaker, conductor, and terminals must be rated for use at that rating. This process follows a 'weak link' method, and the rating of the 'weak link' must be used when using Table 310.16. Example: If you have a panelboard rated 75c, a breaker rated 75c (not 60/75), a conductor rated at 75c, and equipment (such as the range) rated at 75c, you are allowed to use the 75c column. If any component is rated lower, everything must be used at that lower rating. **If there is no explicit marking on the range indicating use at 75c or 90c, the range is assumed to be 60c. The same is applicable to all loads.** There is a special circumstance with breakers marked "60/75c"...

If you have circuit breakers marked "60/75c", and they are installed together (such as in a 42 circuit panel), you must use the breaker at the 60c rating, and thus size your wire using the 60c column. If the breaker in question is in an enclosure by itself, again marked "60/75c", you may use the breaker at its 75c rating. Check the ratings of the enclosure, breaker, conductor, and terminals, and you may be able to use a higher rating than 60c. (XHHW is rated at 90c in dry and damp locations, and 75c in wet locations.)