Editing Ringer equivalence number

{{short description|Indication of the electrical load on a telephone line}}
The '''ringer equivalence number''' ('''REN''') is a [[telecommunications]] [[measurement|measure]] that represents the [[electrical load]]ing effect of a [[telephone]] ringer on a [[telephone line]]. In the United States, '''ringer equivalence''' was first defined by [[U.S. Code of Federal Regulations]], [[Title 47 CFR Part 68|Title 47, Part 68]], based on the load that a standard [[Bell System]] [[model 500 telephone]] represented, and was later determined in accordance with specification ''ANSI/TIA-968-B'' (August 2009).  Measurement systems analogous to the REN exist internationally.

==Definition==
The ringer equivalence of 1 represents the loading effect of a single traditional telephone ringing [[electrical network|circuit]], such as that within the Western Electric [[model 500 telephone]]. The ringer equivalence of modern telephone equipment may be significantly lower than 1. For example, externally powered electronic ringing telephones may have a value as low as 0.1, while modern line-powered telephones, in which the ringer is powered from the telephone line, typically have a REN of approximately 0.8.

In the United States, the FCC Part 68 specification defined REN 1 as equivalent to a 6930 [[Ohm (unit)|Ω]] [[resistor]] [[Series and parallel circuits|in series]] with an {{gaps|8|μF}} ([[Farad|microfarad]]) [[capacitor]].  The modern ANSI/TIA-968-B specification (August 2009) defines it as an [[electrical impedance|impedance]] of {{gaps|7000|Ω}} at {{gaps|20|Hz}} (type A ringer), or {{gaps|8000|Ω}} from {{gaps|15|Hz}} to {{gaps|68|Hz}} (type B ringer).

==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.

==International specifications==
[[File:Aansluitfactor.jpg|thumb|In the Netherlands all telephone equipment shall carry a blue label with the ringer equivalence number - in this case 1.5]]
In the [[United Kingdom]] a maximum of 4 is allowed on any [[British Telecom]] (BT) line.<ref>{{cite web|url=http://www.britishtelephones.com/ren.htm|title=Ringer Equivalence Number (REN)|last=Anon|publisher=BOBS TELEPHONE FILE|access-date=28 May 2015}}</ref>

In [[Australia]] a maximum of 3 is allowed on any [[Telstra]] or [[Optus]] Line.<ref>{{Cite book|url=https://www.telstra.com.au/content/dam/tcom/personal/help/pdf-b/017153a00-complete-home-cabling-guide.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://www.telstra.com.au/content/dam/tcom/personal/help/pdf-b/017153a00-complete-home-cabling-guide.pdf |archive-date=2022-10-09 |url-status=live|title=Cabling of premises for telecommunications – A complete guide to home cabling|date=26 August 2013|publisher=Telstra Corporation|page=182}}</ref>

In Canada it is called a ''load number'' (LN); which must not exceed 100.  The LN of each device represents the percentage of total load allowed.{{citation needed|date=January 2014}}

In Europe 1 REN used to be equivalent to an 1800 Ω resistor in series with a 1 μF capacitor.  The latest [[ETSI]] specification (2003–09) calls for 1 REN to be greater than 16 kΩ at 25&nbsp;Hz and 50&nbsp;Hz.

==References==
{{Reflist}}
* {{FS1037C}}
* [[American National Standards Institute|ANSI]]/[[TIA-968-B]]
* [[European Telecommunications Standards Institute|ETSI]] TS 103 021

[[Category:Telephony equipment]]
[[Category:Equivalent units]]