Help identify this component (part of switch de-bouncing?)
This is a Hongzhi Enterprises (HEL) brand metal-oxide varistor.

The website doesn't mention pending safety approvals, but this part has both UL Recognized component and (what looks like) CSA marks on it. It's not surprising that the website is a little out of date, I've seen it quite often with offshore smaller suppliers.

I've never used this brand of part, so I cannot speak for its robustness.

Specs:



I agree with others that this is most likely intended as a transient clamp meant to suppress the inductive kickback of a de-energized relay coil.