Home > HERE'S HELP, including wire color codes, telecom terms, RJ stuff, more > Polarity detection con job

Polarity detection con job

Polarity detection con job
Like all DC electrical circuits, phone wiring has polarity.

Each phone circuit consists of two wires in a pair. One wire, with positive electrical polarity, is called the "tip" and is traditionally green within a phone jack, the other is negative, called "ring", and is red. The tip and ring terms come from the parts of an old-fashioned telephone switchboard plug.

(An easy way to remember this is that both "ring" and "red" begin with "r," and that "tip" ends with "p," which begins the word "positive.")

While it's nice to maintain "proper" polarity, it seldom provides any real advantage with modern phone equipment.

Until phones became consumer products in the 1980s, touch-tone phones could not make calls unless they were connected with proper polarity. Indeed, some phone companies had their installers deliberately provide service to homes with reverse polarity, to stop the use of "illegal" phones.

When phones started being sold in stores, they incorporated polarity guard circuits, so they would work fine with correct or reversed polarity, to maximize the chance that a phone would work when it was plugged in, and minimize the number of phones being returned to stores.

The polarity guard circuit is an intrinsic part of virtually every phone, phone system, fax, modem, and phone-like gadget sold today.

Because of this, the widespread appearance of polarity indicators on telephone buttsets, tone generators and multifunction testers is pretty much a waste of money and resources, but manufacturers seem reluctant to delete the feature.

The polarity issue has become a last refuge of lazy or clueless tech support people. Very often when someone calls a manufacturer's help line because of a problem with a fax machine or modem or other device, and the technician has no clue as to what is causing the problem, the caller is instructed to go check the polarity and call back later (when, hopefully, someone else will take the call).