The Model R-400 is a static 28 Volt DC Ground Power Unit designed for electrical and mechanical simplicity, physical ruggedness and component accessibility, all contributing to highly reliable operation, ease-of-use and easy maintenance. The R-400 accepts three-phase, 50/60 Hz, 208/230/380 or 460 VAC Input Power, allowing the unit to be used virtually anywhere in the world. Built-in safety features include heavy-duty thermostats in the input control circuit, which are designed for thermal overload protection, and automatic shut-off by an airflow sensor in the event of fan failure. The robust design of the R-400 heavy-duty power transformer ensures easy handling of high-current demands, without compromising reliability and long life.

Multiple taps on the transformer secondary allow the output voltage to be adjusted, and a resistor network permits the output current to be limited. These functions are conveniently controlled from the front panel using multi-position switches. The R-400 DC Output is fully filtered to eliminate ripple voltages and spikes from entering avionics, and to suppress RFI energy produced by the transient generating circuits to better than MIL-STD-461A. In addition to its highly rugged construction, the R-400 offers the user many ergonomic and convenience design features such as separate, easy-to-read voltage and current analog meters, and large, pneumatic rear-wheel tires for ease-of-mobility on the ramp of in the hangar. Additional standard features include a 115 VAC convenience duplex outlet for accessories, lighting of power tools, and side cable hooks for storage of input and output cables.