When you are using non-metalic boxes there is nothing in the NEC requiring EGCs from seperate circuits to be tied together.
That is not how I read 250.148.
Interesting.
How is a 15 amp lighting circuit associated with a 20 amp receptacle circuit?
I have argued this before with George S and he pretty much convinced me that it does not require all circuit EGCs to be connected together.
I read that section as saying that any EGC that is associated with any circuit in the box must be connected to all other EGCs that are associated with all other circuits in that box. Yes, I know we have discussed this before, but I don't think the wording is clear.
It comes down to the particulars of what the conductors do after entering the box...
If both circuits pass through the box without splice or termination, no interconnection or bonding required.
If one circuit passess through while the other is spliced and/or terminated within the box, no interconnection required, but bonding of the spliced and/or terminated circuit's EGC to grounding terminals, metallic box, etc. is required.
If both circuits are spliced and/or terminated, interconnection and bonding applies to both.
[edit to add: the preceding does not apply to isolated grounding conductors]