I have a EVGA 1500 Classified and am learning how to build my first high end PC in 12 years. Since the '90s something called Power Supply "Rails" was invented and I think it has something to do with the GPU.

What are power supply rails (electrically speaking) and how should I use them intelligently (or not) in a custom build?


Rails are independent power channels.

For example:

Rail 1   5 Volt 20 Amp
Rail 2   5 Volt 30 Amp

You have a total of 50 Amp at 5 volt, but they are isolated.

Positives: A electrical short on 1 rail will not effect the other rail and vice versa.

Negative: A device requiring 35 Amps at 5 volts can not be connected since neither rail has that much.

Video cards are generally placed on a separate rail, whenever possible, since they consume so much power.

The same principles apply for 3.3V and 12V.

If any rail drops below 5% of the stated voltage you need to move something to a different rail. 5 volt can go to 4.75, and 12V can go as low as 11.4V (but should not)

You need to check the rails under load and not under idle.

  • With a 1500W power supply you should not have any trouble. The power supply listed has 8 independent 12 volt channels. Just remember you can not place more than 20 amps load on any single channel. – cybernard Apr 7 '13 at 14:58

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