Question on sizing a feeder

Based on the question below, should I calculate the feeder based on the (1) calculated load or (2) overcurrent protection?
Any advise is appreciated.

How many sets of THW conductors are required for a feeder with a 1,000-amp overcurrent protective device that serves a calculated load of 900 amperes?

1. two sets of four THW per raceway of 500 kcmil with grounding
2. three sets of four THW per raceway of 350 kcmil with grounding
3. two sets of four THW per raceway of 600 kcmil with grounding
4. three sets of four THW per raceway of 400 kcmil with grounding
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Based on the question below, should I calculate the feeder based on the (1) calculated load or (2) overcurrent protection?
Any advise is appreciated.

How many sets of THW conductors are required for a feeder with a 1,000-amp overcurrent protective device that serves a calculated load of 900 amperes?

1. two sets of four THW per raceway of 500 kcmil with grounding
2. three sets of four THW per raceway of 350 kcmil with grounding
3. two sets of four THW per raceway of 600 kcmil with grounding
4. three sets of four THW per raceway of 400 kcmil with groundin
You always have to take both into account. However, sometimes you are allowed to use the next higher standard rating of an overcurrent device if it does not match your conductor ampacity.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
As Bob stated this question seems to ask if you understand the next size up rules, 800 amps or less {240.4(B)} and over 800 amps {240.4(C)}. Since it exceeds 800 amps (B) cannot be applied so the conductors need to be a minimum of 1000 amps due to the 1000 amp OCPD. That means the only possible answer is #4.
 
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