I purchased a rod potentiometer and was surprised to see it came with a 4th wire. The manufacturer said it was a ground, though the wiring diagram didn’t even mention it. 

What’s the purpose of a separate ground wire?

I’m intending to have the potentiometer referenced to my ground plane and 3.3 V. I assume I should just tie the extra ground to my ground plane too.

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  [1]: https://i.sstatic.net/sdjLM.jpg