I'm trying to size a 480V-120/240V single phase dry type transformer that will feed a panelboard that will power (4) 240V 50A NEMA 6-50R welding receptacles. Does NEC require that I assume that all (4) welding receptacles will be used at the same time? I believe this would require a 50KVA (208.3A) dry-type transformer to get the required 200 amps. Or is it safe to assume that not all welding receptacles will be used at the same time? If so, how many welding receptacles should I assume will be used? Thanks.