I may be in left field. But you can use one disconnect for two panelboards as long as the panel has LESS than 10% of its branch circuits hooked to a neutral (lights and appliances). For example panelboards supplying 480, 220 or 208 loads (Welders in a shop). But the main must not be rated more than the panelboards. Again maybe I'm in left field but that is what I get out of 408. Dan
