This standard sets terms, test methods, test circuits, measurement procedures and preferred result values for series connected, self-restoring current-limiter components used in low-voltage telecommunication circuit surge protection. It is only applicable for components in telecommunications circuits with sinusoidal ringing voltages up to 150 V rms at 15 Hz to 70 Hz and dc powering voltages up to 400 V. The self-restoring current limiters covered by this standard have the following properties: - Excessive current causes a transition from a low-resistance state to a high-resistance state - Reverts to a low-resistance state when the excessive current ends - Directly operated by the current flow through the component - Solid-state (no moving parts) - Withstands specified levels of impulse - Withstands specified ac voltage levels when in the high-resistance state Examples of this type of current-limiter technology are positive temperature coefficient (PTC) stepfunction theremistors of ceramic or polymeric material and silicon semiconductor based electronic circuits. This standard does not cover self-restoring current-limiter components used in other applications, such as heaters, inrush-current limiters, or sensing devices. Current interrupting type components, which reduce the current to zero by a mechanical circuit break, are not covered by this standard. In this standard, a telecommunications circuit is a circuit that uses metallic conductors to handle the remote transmission of information, such as data, communications, and signalling.