By "power panel" do you mean a breaker panelboard or load center? If so, there isn't any. My company builds remote power panels (RPPs) for use in data centers and such which provide up to 400 amps at 208-V three-phase. There is minimal ventilation because it isn't needed; the connections and bussbars are designed to dissipate as little power as possible since that would represent a loss of power which isn't being delivered to the load.