Ampacity of Conductors in air

I am having problems calculating RCA. I know how to calculate Ri for the
insulation but cannot seem to arrive at the same current value as per NEC
table. The example given at
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ampacity of No 2 conductor uses RCA = Ri + Rsd + Re and is 120A but
that is for conductor in conduit. I need to calculate RCA for a conductor in
air which should be 190A at 90degC conductor and 30degC ambient.
Can you shine some light on the subject.
Greg.
Reply to
Gregory Cohen
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for ampacity of No 2 conductor uses RCA = Ri + Rsd + Re and is 120A but
You will need the NM paper. Annex B of the NEC will also shed light on the subject since these tables are a computer run of NM calculations. Ri and Re would apply, but Rsd would not.
Reply to
Mr. Smith
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for ampacity of No 2 conductor uses RCA = Ri + Rsd + Re and is 120A but
Based on the referenced calculation Rsd would be eliminated with cables in free air. Additonally, the calculation for Re would have to be modified for cables in free air. Re is now for a one inch conduit in free air.
Reply to
Mr. Smith
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for ampacity of No 2 conductor uses RCA = Ri + Rsd + Re and is 120A but
Re=9.5N'/1+1.7Ds'(e+0.41) n' is number of conductors = 1 Ds' is diameter of cable = 0.382 in. for No. 2 XHHW e is emissitivity = 0.5 for dark cable Re = 9.5(1) / 1+1.7(0.382)(0.5+0.41)
Reply to
Mr. Smith
Thank you for your help. Greg.
Reply to
Gregory Cohen

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