In electrical engineering, a common rail (shortened to COM) is a shared path between different electrical routes in an

electrical circuit An electrical network is an interconnection of electrical components (e.g., batteries, resistors, inductors, capacitors, switches, transistors) or a model of such an interconnection, consisting of electrical elements (e.g., voltage sour ...

. For example, a device or circuit board might have a power rail or a ground rail, which components are attached to, so all the electrical charge flowing through different components is drawn from/collected into a single conductor line. The

ATX ATX (Advanced Technology eXtended) is a motherboard and power supply configuration specification developed by Intel in 1995 to improve on previous de facto standards like the AT (form factor), AT design. It was the first major change in comput ...

standard for PC

power supplies A power supply is an electrical device that supplies electric power to an electrical load. The main purpose of a power supply is to convert electric current from a source to the correct voltage, current, and frequency to power the load. As a r ...

defines a set of common rails as to ground the power, these rails are designated as COM and all have black wires.{{cite web, url=http://pinouts.ru/Power/atx_v2_pinout.shtml , title=ATX 24 pin power supply connector pinout diagram @ , publisher=Pinouts.ru , date=2013-08-24 , accessdate=2014-01-03

References

Electrical engineering Electricity