i need a little help!

[surf more]

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!!!

 

[electricalperson]

i get 255 amps based on 310.75 copper conductor 90 degree c and 200 amps aluminum in 310.76

 

[surf more]

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--

 

[electricalperson]

what book is this from?

 

[surf more]

jcr 2005---just sample questions

 

[electricalperson]

maybe the publishers website has a link to corrections. or maybe we are both wrong :grin:

 

[masterinbama]

Ampacities are different for 5KV cable. My Southwire chart says 305 amps

 

[cadpoint]

Surf, Southwire's spec. sheet would not be a reference point in respects to your test... NP Bama...

 

[surf more]

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!!!!!!!!

 

[cadpoint]

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

And the de-fact-o is: the hardest test on the Coast ! Good Luck

 

[al hildenbrand]

So, from 240.101(A), 6 x 255A = 1530 A.

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

 

[surf more]

And the de-fact-o is: the hardest test on the Coast ! Good Luck

i agree --blew it my first by couple of points..the wording is so tricky--was great learning experince if nothing else.
by far hardest test i have ever taken!!!!!!!

 

[surf more]

So, from 240.101(A), 6 x 255A = 1530 A.

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

that is the reason i came to this forum ,that is what i was maybe thinking 1200 came up!!!

 

[westernexplorer]

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

 

[hardworkingstiff]

i agree --blew it my first by couple of points..the wording is so tricky--was great learning experince if nothing else.
by far hardest test i have ever taken!!!!!!!

I thought the W. VA test was harder. Took it in 1993, took the intermediate in NC in 1996 and the unlimited in 2004.

(passed all 3 1st time)

 

[Jim Shorts]

Try 230.208 also.