This document provides guidelines for applying audio tones over voice grade channels for power system relaying. Included are sections on transmitting and receiving equipment, leased voice grade channels, application principles, installation, and testing. The primary purpose of this document is to guide the power system user in applying, installing, and operating audio-tone protective relaying systems over voice grade channels. Secondly, it is to provide a reference for equipment manufacturers engaged in the design and application of relaying equipment and for telephone personnel engaged in providing telecommunications channels for audio-tone protective relay schemes.

Review and revise the existing standard to incorporate current industry practice and technology.

Since this document's last reaffirmation, many changes have occurred in the telecommunications industry. The purpose of this project is to bring this guide up to date with the current technology.