647.7 (A) (4) Unique Receptacle Configuration

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nc5p

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Tempe, AZ
I am designing a test station using balanced "technical power". Could someone elaborate on what the code means by unique configuration? I take it to mean that 5-15/5-20 straight blade devices cannot be used as they are used in grounded neutral service. Can I use locking devices? Does "identified for use" mean they are specifically listed for this class of service or is there some leeway there?
 
By "unique," they mean a configuration different from any others in use in the premises. A twist-lock is one example, a welder receptacle is another.
 
hubbell has a series of twistlocks called 'variload' if i recall correctly, designed for use with non standard power in labs and similar environments where use of nema devices would not be appropriate. might be something to take a look at.

edit: just looked in the book, all these connectors are 5 wire
 
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