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
Can you shine some light on the subject.
Greg.
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
Can you shine some light on the subject.
Greg.
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.
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.
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)
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