Please tell me about Power Supply Rails

[Reuben 1]

I am looking for new Power Supply Unit. I am interested in buying Corsair Power Supply Unit model no CMPSU-650TX which is single rail. What are rails actually? Are they any connectors or plugs? Why we need more than one rails.

[Howitzer]

Power Supply Rail or voltage rail is a single voltage provided by a power supply unit (PSU).In current ATX computer PSU there are total of three primary voltage rails. Those are
1. +12V can be up to 5 max
2. One +3.3V
3. One +5V
Above are providing power to various components of computer system.
+12V: It is the most important voltage rail. It provides power to those components who takes more amount of current. The components are actually Graphics card, CPU, Hard Drive and other storage components. +12 V rail has to be good since small current fluctuation can cause malfunction in component. As many as Five +12 V rails are available in PSU. Each rail will have its own wires and connector.
+5V: It has its own set of wire and connectors.
+3.3V: It has its own set of wire and connectors. It has its own circuitry to generator voltage. Since Microprocessor chip technology improving day by day.ATX standard added 3.3V rail to power new chips

[samar69]

Hello,
Intel IIRC has introduced one specification few years back which is limiting +12v rails to 18amps. So according to it if we have 54amps of PSU then there has to be 3 +12v rails due to above limitation so none of them can pull more than 18amps. Today there is more demand for larger single rail PSU. According to me rails can be two or more but has to build correctly so no malfunction can be occur.

[Mayur_Jain]

ATX 2.0 spec puts limitation of 240vA on single rail i.e. 12v rails are limited to 20A. And limitation was removed from ATX 2.2 spec and reduced to recommendation instead of requirement. So consumer doesn’t have to worry about which cable connected to which device. The model HX520 has spec as Triple rail design but it’s actually single rail it makes it easier for compatibility and for safety.