i need a little help!

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surf more

Senior Member
Location
eastern NC
came across a question---


a 4600 volt,4/0 3 conductor copper cable is in isolated conduit in air.what is the max allowable rating of a circuit breaker used to protect the ungrounded conductors?


answer key=1200amp


i went to 310.75,and 240.101 but for some reason,,i am totally missing it.

if someone could break this down for me i would be very thankful!!!!!!!!!!
i went threw problems like this num...times,but my problem now is i took a break from this stuff--and it seems it was to long of a break!!!
 

surf more

Senior Member
Location
eastern NC
gottcha that is what i was reading 255---maybe misprint????----i posted because i did not know if i was supose to multiply or something---i was really boggled at the answer key!!!!!

just did a few more similiar problems ,and got all correct.
guess answer key---misprint!!!

if someone see something missing ---CHIME AWAY--
 
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surf more

Senior Member
Location
eastern NC
all i will be able to use when i take LIMITED electrical in NC.
test center will provide=2008 nec
2 sheets paper
#2 pencil
basic calculater


i am just answering random questions out of some sample packets!
my whole deal was i just wanted to make sure i was not going CRAZY!
again my answer was 255 also,and my answer key 1200!!!If anyone disagree with 255 please speak up!!!!!!!!
 

al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
So, from 240.101(A), 6 x 255A = 1530 A.

What's missing is the >600V equivalent of 240.6 (Standard Ampere Ratings.)
 

westernexplorer

Senior Member
I would guess it is a misprint.......NEC 310.76 , 4/0 AL would fit...X 6 would give you the 1200 AMPS....maybe....unless the answer is a misprint.....LOL
 
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