Tip and ring

Floating both conductors, i.e. not referencing either one to ground, minimizes the effect of interference from any nearby alternating current (AC) power wires.

The terms tip and ring originated in the early days of telephony when telephone operators used plugs to connect customer calls.

In the middle 20th century, long loops in many rural areas of North America used range extenders, which operated at 100 or 130 volts to ensure reliable signaling.

When Touch-Tone service was introduced in the 1960s, the tone generator for DTMF required correct polarity as it depended on the line D.C. voltage for operation.

However, some special circuits, such as some direct inward dialing (DID) trunks, T-1 lines, and ground start lines connected to field-side (terminal) equipment, e.g., a corporate private branch exchange (PBX) switch, correctly operate only with proper tip and ring polarity.

Some telephone technicians used mnemonic phrases, such as red-right-ring-rear, or ring-right-red-rough, to remember that the red wire connects to the right-side post in the wall jack and to the ring on the plug and to the rear lug on main distribution frames.