NSI-63 is a railway signaling system used for interlocking on the Norwegian railway network. It is based on relays and was developed by Norsk Signal Industri for the Norwegian State Railways (NSB) during the early 1960s. The systems are installed at railway stations and passing loops and consist of single relays built form drawings. The system is simple, robust and economical for smaller stations on single-track railways. The system makes use of track circuits for train detection.