This guide covers the application of component air gaps, gas tubes, MOVs, and avalanche junction semiconductor surge-protective devices for use within surge protectors, equipment, or systems involving lowvoltage power, data, communication, and/or signaling circuits. This guide is intended to be used with, or to complement, the related documents referred to in 2.1. The present guide only covers the application of component air gap and gas tube surge protective dev ices for use in low voltage circuits. The purpose of this project is to revise IEEE C62.42 to include guidance for the application of component varistors and av alanche junction semiconductor surge-protective devices. Revision Standard - Superseded. Assistance in selecting the most appropriate type of low-voltage component surge-protective device (gas tube, air gap, metal-oxide varistor, or avalanche junction semiconductor) for a particular application is provided. Evaluation of the characteristics of each device to meet specific service requirements is also given.