Under ground conductor ampacity rating.

Merry Christmas
Status
Not open for further replies.
T

twsteed

Member
Location
Douglas, Wyoming
My question involves 2/0 aluminum USE, 75 degree C wire and terminations, triplex cable. The conductors originate and terminate outside of a building. If I use table 310.15(B)(2)(a) and an underground temperature of 59 degrees F, can I increase the ampacity and OCP of the conductor?
Less than 10 feet of conductor above grade on either end. 1.15 x135=155 amps.
 
what about the equipment at point of termination ? What temperature termination will that allow (ref: 110.14) ?
 
Less than ten feet above grade at either end, OK. But what is the length underground?
The exception I am thinking of allows 10' or 10% whichever is smaller.
 
Do not know of any 10 percent length exception, both ends would be about six feet long and about a sixty foot long underground length. The terminations on both ends are rated for 75 degrees C.
 
110.14 is going to be the limiting factor. Regardless of the adjusted amapcity of the conductor, the allowed ampacity can not exceed the provisions given in 110.14, in the case of 20 AL that would be 135 amps.
240.4(B) would allow you a 150 amp overcurrent device but your calculated load could not exceed 135 amps.
 
Gentlemen, thank you for your input, but I respectfullydisagree. 310.15(B) allows for the" temperature correction and adjustmentfactors shall be permitted to be applied to the to the ampacity for thetemperature rating of the conductor".
I am using the 75 degree C column in the "AmbientTemperature Correction " table, 310.15(B)(2)(a). according to the table, Iam not exceeding the 75 degree limitation.
 
310.15(B)(16) shows the allowable ampacity of 2/0 AL at 135 amps.
Adjusting for ambient my well change the ampacity of the conductor, and 110.14 limits you to that an ampacity rating for 75? terminations, IMO.
Hopefully others will have an opinion also.
 
Status
Not open for further replies.
Top