The 203-1-1-42-252-1-1 is a Type 203 supplementary protector designed for circuit protection with inverse time delay characteristics. This unit features a 400 Hz long delay (designation -42) with a 20 ampere current rating (designation -252), providing reliable overcurrent protection in electrical systems. The protector incorporates a rocker handle construction with standard U.S.A./CSA construction and operates with a delay time of 1.50 seconds as specified in the design documentation. The device includes impedance characteristics suitable for AC applications at 60 Hz and 400 Hz frequencies, with DC resistance and impedance values documented in the technical specifications. This supplementary protector is commonly used in power distribution systems, industrial control circuits, and equipment requiring coordinated overcurrent protection with time-delay characteristics to prevent nuisance trips while maintaining system safety.