This adapter allows you to plug into your 4-prong NEMA 14-30 Dryer Outlet and gives you two 20 amp 120 volt duplex Outlets, they will accept both NEMA 5-15 and 5-20 plugs so you can plug common 120 volt household items into it.  This adapter fully utilizes both phases of your 240-volt Dryer outlet, each duplex Outlet is on its own phase and you may draw up to 20 amps out of each duplex Outlet. This means you can draw all 20 amps out of one Outlet of the duplex or 10 amps out of each of the top and bottom receptacle of each duplex Outlet, or any combination that adds up to 20 amps. The great thing about this adapter is you can do this on EACH duplex Outlet, that means each duplex Outlet can support a maximum of 2400 watts, giving you access to 4800 watts maximum between both duplex Outlets. 

Following the NEC codes 80% rule of thumb it states any continuous load should not be more than 80% of the rated capacity for maximum capacity. The NEC code's definition of a continuous load is one that runs for more than 3 hours so this would generally not include window Air Conditioners, Refrigerators, Freezers, Air Compressors, Welders and Dryers for example. If you are using equipment such as Electric Vehicle Charging Stations (EVSE), lights or any loads that can run for more than 3 hours then those are deemed continuous loads and you will need to limit your total load on each duplex Outlet to 16 amps or 1920 watts, with two duplex Outlets this gives you access to a total of 3840 watts continuous.

This adapter is built for a long life with the outlets house in a 4"x4" metal box.