Can someone explain how to size grounds for parallel conductors for a SDS I still cannot understand how this is accomplished. Ex. 1600A feeder 4 sets parallel 600?s. so the total cmill area is 1680cmills. 12.5% of that is 210cmills that would mean a 4/0 would be required as my ground. But 250.30(8)(b) states the size of the ground conductor in each raceway shall be based on the ungrounded conductors in the raceway but not smaller than 1/0, so does this mean 12.5% of a single 600 as that is the largest phase conductor in that conduit? If you had a 3000A service with 7-sets of 600?s 12.5% would be 525000 that would mean a 600kcmil grd. In each conduit? Is that correct or would it be 12.5% of a single 600 in that case a 1/0 would be fine as the min. size allowed to be paralleled??