What is meant by rail voltage?

Question

What is meant by rail voltage?

Answer 1

A power supply rail or voltage rail refers to a single voltage provided by a power supply unit (PSU) relative to some understood ground. Although the term is generally used in electrical engineering, most people encounter it in the context of personal computer power supplies.

When a power supply has multiple-rail overcurrent protection, if any rail reaches that limit, the entire power supply will shut down. This is not associated with any overheating or increase in ripple voltage by the power supply as a whole, as might be caused by an overall overload. The only reliability penalty from operating a rail close to its current limit comes from the risk of triggering the shutdown.

When a power supply has multiple-rail overcurrent protection, if any rail reaches that limit, the entire power supply will shut down. This is not associated with any overheating or increase in ripple voltage by the power supply as a whole, as might be caused by an overall overload. The only reliability penalty from operating a rail close to its current limit comes from the risk of triggering the shutdown.

The original IBM PC power supply unit (PSU) supplied two main voltage rails: +5V and +12V. It supplied two other voltages, -5V and -12V, but with limited amounts of power.

Most of the standard silicon microchips of the time operated on 5V power. Of the 63.5 watts these PSUs could deliver, most of it was on this +5V rail.

The +12V supply was used primarily to operate motors. Fan motors, floppy disk drives and later, hard disk drives. As more peripherals were added, more power was delivered on the 12V rail. However, since most of the power is consumed by chips, the 5V rail still delivered most of the power.

The -12V rail was used primarily to provide the negative supply voltage to the RS-232 serial ports.

Answer 2

As in the over head pantographs ?, it would be the voltage in the over heads that power the loco's.

Answer 3

If you mean rail in the sense of an amplifier swinging "rail-to-rail" it means the full range of the DC supply voltage.  So for example, if you have a dual supply giving out +5 V and -5 V then the supply rails are +5 V and -5 V.  If your supply is only +5 V then the rails are 0 V (ground) and +5 V.