Reliable Power Supply

Dear Sirs,

Are there available any sources which give any recommendations when plant power supply can be considered as an reliable.

For example: we have two Main Supply Points, each is supplied from: a) Local Power Plant external power supplier . Each refinery plant is supplied from two Local Supply Points which are fed from both Main Supply Points.

For a few most critical plants we have also third power supply from third, another, Local Supply Point, but still fed from two Main Supply Points , mentioned before. 

Is this third power supply can be considered as an reliable?

Any help will be appreciated.

Best regards.

Thanks Zauberberg!

Kind regards

All 17 Annexes of IEEE 493-2007 can be downloaded from IEEE web site: https://standards.ie...7_downloads.zip

If the link above does not work, go to: https://standards.ie...d/493-2007.htmland scroll down to use the link under "Additional Resources Details".