Correct grounding of metal junction box w/splices for 3 circuits

[Noah Katz]

I have 3 circuits (microwave, disposal, and dishwasher) entering a metal box where the THHN wire will be spliced to Romex.

To ground the box, do I just need to pigtail off of one circuit's ground wire and attach to the box, or do I pigtail all 3 circuits' ground wires together?

In case you're wondering, the conduit is metal, which I believe is sufficient for grounding, but I don't trust the fittings' set screws.

 

[Dennis Alwon]

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