What is a typical twist lock plug type for server stuff?

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http://hardforum.com – I ran two 20a plugs to my rack and used wire rated for 30a. I was thinking, I should swap those out for twist lock and just buy more wire and run two more 20a circuits. What type of plug is typical for server stuff, and is it 120v or 240v? I want to run whatever I am more likely to need in the future for say, a big UPS, rectifier, etc so that it's there and ready to go. I'm guessing L6-30? Also do these plugs typically fit in a standard wiring box? Never installed one before. (Hardware)