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Ringer Equivalency Numbers And You

Wednesday, April 23, 2008

One of the things you've never probably heard of is something called REN, or Ringer Equivalency Number. In short, it is the amount of electrical load that a telephone ringer puts on a line. Modern telephones all have a REN value printed on the bottom of the telephone.

A REN value of 1 represents the loading effect of a single "traditional" telephone, for example a Western Electric Model 500 desk telephone. Most telephone these days have a REN far less than that, though some have more. My cordless telephone has a REN of .08.

Why is this even an issue? There is a difference between what an analog telephone adapter is able to support in terms of REN and what a typical landline supports. A Linksys SPA-2000 supports a REN of 3, whereas a typical landline supports a REN of 5.

Why does this matter? If you're distributing VoIP throughout your home and you have a lot of old telephones, not having enough REN will prevent your telephones from ringing, or cause them to ring improperly. This is because there is not enough ring voltage being sent to the phones!

There are a couple of choices to resolve this problem: reduce the load by unplugging or swapping phones to ones with lower REN values, or increase the REN output. How do you do that? Using a device like the Ring Voltage Booster II from Mike Sandman Enterprises.

The Ring Voltage Booster II takes whatever ring voltage it gets and boosts it to an acceptable level. You plug one end into your analog telephone adapter, the other into your telephones. The Ring Voltage Booster II will take a ring voltage as low as 30VAC RMS and boost it to 90VAC at 20 cycles. It also supports a REN of 7.5, meaning you can plug in 7 of those old Western Electric phones and it will ring them all!