310-16

[kimrichi]

when we have a wire with specific insulation[thhn] and the amp is less than 100 amwhich column do we use 60 or 90

 

[Twoskinsoneman]

when we have a wire with specific insulation[thhn] and the amp is less than 100 amwhich column do we use 60 or 90

There is a lot that goes into conductor rating questions. But since you mention less than 100 amps I assume this is a question/discuss regarding 110.14(C). That is where you want to start.

To get a good in-depth understanding I suggest you do some thread searches. You may find one or two that discusses it

 

[infinity]

You would use 60? C unless you can meet one of the conditions in 110.14(C) where you would be permitted to use 75? C if the terminals on both ends of the conductor are rated for 75? C.

(C) Temperature Limitations. The temperature rating associated with the ampacity of a conductor shall be selected and coordinated so as not to exceed the lowest temperature rating of any connected termination, conductor, or device. Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction, or both.
(1) Equipment Provisions. The determination of termination provisions of equipment shall be based on 110.14(C)(1)(a) or (C)(1)(b). Unless the equipment is listed and marked otherwise, conductor ampacities used in determining equipment termination provisions shall be based on Table 310.16 as appropriately modified by 310.15(B)(6).
(a) Termination provisions of equipment for circuits rated 100 amperes or less, or marked for 14 AWG through 1 AWG conductors, shall be used only for one of the following:
(1) Conductors rated 60?C (140?F).
(2) Conductors with higher temperature ratings, provided the ampacity of such conductors is determined based on the 60?C (140?F) ampacity of the conductor size used.
(3) Conductors with higher temperature ratings if the equipment is listed and identified for use with such conductors.
(4) For motors marked with design letters B, C, or D, conductors having an insulation rating of 75?C (167?F) or higher shall be permitted to be used, provided the ampacity of such conductors does not exceed the 75?C (167?F) ampacity.
(b) Termination provisions of equipment for circuits rated over 100 amperes, or marked for conductors larger than 1 AWG, shall be used only for one of the following:
(1) Conductors rated 75?C (167?F)
(2) Conductors with higher temperature ratings, provided the ampacity of such conductors does not exceed the 75?C (167?F) ampacity of the conductor size used, or up to their ampacity if the equipment is listed and identified for use with such conductors

 

[augie47]

when we have a wire with specific insulation[thhn] and the amp is less than 100 amp which column do we use 60 or 90

I am in agreement with the other replies, but note that "which column you use" depends on the function. If it is a conductor with a 90? insulation such as THHN you may use the 90? amperage for derating purposes but you have to take into account 110.14(C) and use the appropriate rating for termination.
In addition be aware of limitations in 240.4

 

[Dennis Alwon]

when we have a wire with specific insulation[thhn] and the amp is less than 100 amwhich column do we use 60 or 90

Remember the column that we use is dependent on the weakest link in the circuit. Most terminals today are rated 75C however if you have an older panelboard or termination where the temp. rating is not visible then 110.14 comes into play with 100 amp or less at 60C otherwise the 75C column is used-- assuming the wire is rated 75c or 90c.

The advantage to a 90C wire is that we may start at 90C for derating purposes but the final OCPD cannot be more then the weakest link or usually the 75C column.