Ribbon cable

Ribbon cable is a series of conductive wires running parallel to one another along the same plane. This creates a wide, flat bundle of wires that can, in some cases, be awkward to handle.

Most commonly, ribbon cables are used for connections inside of a device, such as disk drives in a computer.

Color Coding
Typically, ribbon cable is a uniform color. In order to prevent reversed connections and damage to hardware, one edge has a prominent stripe. Under normal circumstances, the side with the stripe indicates which wire is connected to pin 1.

The connector is also normally keyed to prevent incorrect connection.

In a majority of cases, this marking is sufficient for wiring, but when the cable needs to be terminated in multiple segments, it can become difficult to count.

In the case where multiple terminations are required, a specialized rainbow cable can be used. The colors are based on the order of the resistor color codes, with brown being the first, red being the second, etc. As the pattern repeats, each instance of brown would represent wires 1, 11, 21, etc. and red would be 2, 12, 22, and so on.

Sizing
Ribbon cable usually is specified by pin pitch and ways (the number of conductors). The pitch of the cable is the spacing of each conductor, and is typically 1.27mm (0.05 inches).

This spacing allows for the use of a two-row connector with pin spacing of 2.54mm (0.1 inches). The most common use of this is with Parallel ATA cables used for older hard drive connections now being superceeded by SATA.

The number of ways in the produced cables is generally dictated by the availability of standard connectors. As a result, the most common numbers of conductors in ribbon cables are 4, 6, 8, 9, 10, 14, 15, 16, 18, 20, 24, 25, 26, 34, 37, 40, 50, 60, 64 and 80.

Generally, the wire is stranded copper in 0.32 0.32, 0.20, or 0.13 mm2 (22, 24, or 26 AWG). Ribbon cables with finer pitch are available, but should not be confused with Flexible Flat Cable (FFC)

Connectors
The design of ribbon cables is to facilitate the use of insulation-displacement connectors (IDC), which allow for mass termination. An IDC uses sharp contacts that pierce the insulation of the cable so no stripping is necessary. Typically IDC terminations are not intended to be re-used, but with care, an IDC can be removed and reattached.

In hobby electronics, the two most common connections are BT224 connector (or DIN41651) and PCB Transition Headers. Both have 2.54mm spacing, and are seen in ATA connections and ICSP Headers.

Interference
For Digital connections, ribbon cables are ideal. However, in Analog applications, they pose problems. They are inherently good antennas, but only broadcast random signals across a wide band of the electromagnetic spectrum. As a result, there have been FCC regulations created, effectively limiting them to use inside of a device's case.