Help with question please

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rwi

Member
Location
GA.
With a load of 73 amps what is the mimimum size of type USE cable to service this load?
#1 AWG USE
#2 AWG USE
#3 AWG USE
#4 AWG USE
The answer is #3 AWG USE and comes from 2003 irc E3605.4.1 Conductors rated at 60c; E3605.1 and Table E3605.1 (the branch curcuit load of 73 amps will require a wire size whose ampacity is ultimately choosen from the 60c column of table 3605.1. The minimum size type USE that can service 73 amps of load is #3 AWG choosen from the 60c column.

Ok, I read it but I don?t get it. Why is it 60c when USE type is shown under the 75c column???
 
C

cloudymacleod

Senior Member
well because, if u go to nec code book, to article 110-14, it tells u that for the purpose of terminals connections. so for 100amps or less and wire size 14 to#1 use the 60c column, for over 100amps or more and wire size larger than #1, u use the 75c column. and for derating factors u use the 90c column. but for all motor conductors size, u use the 75c column.
 
infinity

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
I agree with Cloudy regarding 110.14, but I'm unsure where he got the reference to motors using the 75 degree ampacity?
 
rcarroll

rcarroll

Senior Member
Location
Fort Collins, Colorado
110.14(C)(1) confuses me. (a) Termination provisions of equiment for circuits rated 100a or less, or marked #14 thru #1 shall be used only for one of the following. Then it gives us 4 options. Can we use option #(3) & use the 75 deg. column? The handbook gives an example using #8, where depending on the temp rating of equipment, #8 can be breakered at 40a or 50 amps. Infinity, option (4) is where, I think Cloudy got his answer for the motors. If anyone can enlighten me, I would definately appreciate it. Thanks, Ron
 
J

Jljohnson

Senior Member
Location
Colorado
rcarroll, how about if me or one my crew installs it, it passes but if it is installed by one of my competitors it fails. That sounds enlightening to me. lol. The way I read it, as long as all terminations are approved for 75 degrees, then you can use the 75 degree column. Otherwise, your stuck with 60 degree.
 
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