Calculation question

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j.hamilton

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I need to know how to answer this question. I missed it on the master electrician test in Kentucky.

You have a two inch rigid conduit with five 1/0 wires at 44 c and the type of wire is thhw what is the amperes drawn?

The three answers given were 68 or 76 or 84

no other information was given
 
I don't really understand the question as written. :-?

You could find the adjusted ampacity for those conductors with the given information:

150 amps (THWN 75 degrees)* .82 (correction factor) * 80% (derating 4-6 CCC in raceway)= 98.4 amps

Still nowhere near the answers you provided unless some info is missing. Is this for copper or aluminum? I assumed copper.
 
090804-0753 EST

I believe the question has incomplete information of two items. Assuming 44 C. is the wire temperature, then there is no temperature given of the conduit. One needs to know temperature difference and thermal resistance to determine power, and in turn current. Second missing information is wire material as was previously mentioned. Then also from somewhere the thermal resistance from the wire in this group of wires to the conduit is need. Presumably this was indirectly available from some NEC table.

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I'm with the others. Consider the situation where the ambient temperature is 44?C. The current on all five conductors would be zero (0).

From there the conductors could have current flowing through them and be at 44?C, but the ambient temperature would have to be of a lower temperature. With the ambient temperature unknown, any one of the three possible answers could be true.
 
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