Re: Parallel conductors
Hi Frank: I assume that the supply consists of a 3-phase, 4-wire sevice system because of the term used (main disconnect switch). Therefore, 8 conductors in one raceway. The equation for this is: conductor ampacity = (load divided by 0.70)(0.5)= conductor ampacity = (400 divided by 0.70) x (0.5)= 285.7. You are allowed to apply the correction factor to the ampacity of the conductor. If 90 degree C conductors are used, and the new current carrying capacity, after application of the correction factors is at least that for which the terminations are rated, ie., 75 degrees C, it will satisfy the NEC. Therefore, 250 Kcmil Cu conductors rated for 90 degrees C will do the job. The next step is to determine the size of the raceway based on the type conductor insulation. If 250 Kcmil, XHHW is used, each conductor has an area of 0.3904 sq in. Four in PVC has a area of 4.503 sq in. 8 x 0.3904 = 3.123 sq in. The grounded system conductor will serve to ground the 400 amp main switch and a grounding electrod conductor must be installed to a grounding electrode system.