The ringer equivalence number (REN) quantifies how much current a device draws from the central office to ring its bell. A standard mechanical telephone bell equals one REN. Telephone companies limit the total REN on a single local loop to ensure enough voltage reaches all devices to trigger their ringers. If the combined REN of all connected phones, fax machines, and modems exceeds this limit, the devices fail to ring on incoming calls.
Heard on the job
The customer complained about missed calls, and it turned out they had four vintage rotary phones on the line pushing the total REN past five.
Insider tip
Solid-state telephones draw much less current than older mechanical bells, often registering at just a fraction of one REN.
Also heard as
- REN