310.16

[garrisonm1]

Im confused on what degree column to use on 310.16 for thhn conductors. Someone told me to use 75degree column and someone else told me to use the 90degree column. What is the reasoning behind each of these degrees.

 

[Guest]

Re: 310.16

It depends on what you're doing, but even if the wire is rated 90, you may have to go 75 because of the connections

Hope that helps. If your question remains unanswered please post back with more details so we can help you.

[ September 20, 2003, 02:53 PM: Message edited by: awwt ]

 

[don_resqcapt19]

Re: 310.16

You can use the 90? column for ampacity adjustments for more than 3 current carrying conductors in a raceway or cable and for the adjustments for high ambient temperature, but you must also apply the rules in 110.14(C).
Don

 

[garrisonm1]

Re: 310.16

Im confused on why the inspector told me that the minimum size conductor for 325 amps is 400 kcmil thhn. Looking at 310.16 90 degree column States that we can use 350 kcmil instead.

 

[roger]

Re: 310.16

Follow Don's post to 110.14(C).

If all terminations and components are listed and labeled 90 deg or higher you could use the 90 deg column for the installation.

If not, you would use the 75 deg column.

The 90 deg column can be used for adjustments as Don said.

Roger

[ September 21, 2003, 04:20 PM: Message edited by: roger ]

 

[earlydean]

Re: 310.16

The section in question:

110.14(C)(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)(1) through (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, D, or E, 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

What this means is that unless UL approves it otherwise, use the 60 degree section of Table 310.16 for wires up to and including 100 amps, and the 75 degree section for wires above 100 amps. The 90 degree section is only used by UL permission for special circumstances and for the ampacity of the conductors for derating purposes. The entire assembly must be rated for the same temperature rating for it to be allowed to use the higher rating. The assembly consists of the lug(s) at the breaker, the neutral bus, the wire, and the lugs at the load, plus any wirenuts in-between. (What is the temperature rating of your wirenuts? How about your bushings?)
You are allowed to use the higher ampacity sections if you use the higher ampacity wire, but only for ampacity adjustments like ambient temperature and more than 3-current carrying conductors. The largest O.C. device cannot exceed the amperage allowed by the 60 degree section of T 310-16 for up to 100 amps, or the 75 degree section for over 100 amps.
Earl