In telecommunication, a ringer equivalency number(REN) is a somewhat arbitrary number which denotes the loading a telephone ringer has on the line. A ringer equivalency number of 1 represents the' loading effect of a single "traditional" telephone ringing circuit. Note that modern telephone equipment may have a REN significantly lower than 1: as a rough guide, externally-powered digital-ring phones may have a REN as low as 0.2, while modern analogue-ring phones (where the ringer is powered from the phone line) typically have a REN around 0.8.
The total REN for a subscriber's line is simply the' sum of the RENs of all devices connected to the line; this number expresses the overall loading effect of the subscriber's equipment on the central office ringing current generator. If the total allowable REN load is exceeded, the phone circuit may fail to ring (or otherwise malfunction). In extreme cases, the telephone service provider may temporarily disconnect an overloaded line to reduce load.
The FXS port supports REN 5, providing the load on your loop does not exceed REN 5, you should be fine.
