Sean wins the rubber chicken! It's from a 'swamp cooler.'
http://www.wonderquest.com/swamp-coolers.htm Used in arid areas, in many situations these low-power units replace energy-hog air conditioners.
They typically have three settings: fan only, low cool, high cool. The "low" and "high" are accomplished by changing the fan motor speed.
The fan motors come with plugs that match the female end that I posted. The motors are 120; one pin feeds the 'low speed' winding, while another pin feeds the 'high speed' winding. The pump plugs in to another receptacle. Both of these receptacles are inside the unit, mounted on the side of the control section.
From a code standpoint, you still need another disconnect on the outside of the unit. Simply unplugging the fan and pump will not turn off power to the control section. It would be most unfortunate, were the fan to operate while you were inside, changing the pump.
Industry standard? Yup! maybe not "NEMA," but many different manufacturers of the units, as well as the replacement parts, use these plugs.
Though, I really ought to take one of these plugs to the supply house, just to drive them nuts
