Editing Ringer equivalence number (section)

==Maximum ringer equivalence==
The total ringer load on a [[subscriber]] line is the sum of the ringer equivalences of all [[information appliance|device]]s (phone, fax, a separate answerphone, etc.) connected to the line. This represents the overall loading effect of the subscriber equipment on the [[telephone exchange|central office]] ringing [[current (electricity)|current]] source. Subscriber telephone lines are usually limited to support a ringer equivalence of 5, per the federal specifications.

If the total allowable ringer load is exceeded, the phone circuit may fail to ring or otherwise malfunction. For example, [[call waiting]], [[caller ID]], and [[ADSL]] services are often affected by high ringer load.

Some [[analog telephone adapter]]s for [[Internet telephony]] require analog telephones with low REN, for example, the AT&T 210 is a basic phone which does not require an external electrical connection and has a REN of 0.9B.