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Is a local indoor FXS analogue telephone port on a router considered ES2, regardless of the working voltage or current?

FXS and FXO are the designations of the ports used by analog phone lines (also known as POTS – Plain Old Telephone Service) or phones. FXS (Foreign Exchange Subscriber) is the port that actually delivers the analog line to the subscriber. 


More frequently, today the Exchange or Network Operator provides “xDSL (VoIP)” signal, which is considered ES1, ID1. In the past this interface more frequently may have been “xDSL over ISDN” or “xDSL over POTS”, which was considered ES2, ID1. 


If a router connected to this interface provides an FXS analog telephone port as an output, the ES classification, incl. external circuit transient voltages, depend on working voltages and current of the generated ringing signals. Generally, these are considered ES2, although it’s important to understand and classify each specific construction.


These interface classifications are based on IEC TR 62102 (Electrical safety – Classification of interfaces for equipment to be connected to information and communications technology networks), which is a guide to the determination of the interface requirements for equipment in terms of safety. Due to the new terminology of IEC 62368-1 and more modern implementations of communication networks, IEC TR 62102 is currently in revision to be aligned.

As the complete answer to this question will depend significantly on the specific construction, you are encouraged to contact UL for an in-depth consultation, either via your local account executive or via https://62368-ul-solutions.com/contact-ul.html.

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