The FCC decreed that the subscriber would be responsible for the 'load' their CPE (Customer Provided Equipment) devices put on their phone line. Some guidelines were established;

• Each device will have a REN ,"ringer equivalency number", marked somewhere on the device.
• The total of all of the RENs on any phone line can not exceed 5.
• Devices that ring at 20 Hrz will have a suffix of 'A' added to the REN.
• Devices that ring at any frequency will have a suffix of 'B' added to the REN.

Typical phone lines have 85 to 105 Volts A.C. superimposed on a nominal -48 Volts D.C. The A.C. current during the ringing cycle is between 20 and 50 milliamps. It will give you a shock!

A similar system exists in Canada, the REN is expressed as a whole number, and the total of all RENs cannot exceed 100.

Press your browser's BACK button to return
goto Telecommunications Tidbits page