I clearly need some educating here. The only 4 pole RCDs with which I'm familiar are designed for 3 phase+neutral use, and I'm struggling to understand how they could work (as RCDs) if you used one of the intended 'phase' paths through it for a second neutral. Are you talking about some other type of 4 pole RCD - or am I just being dim?4 POLE RCD, two neutrals and two lives passing through it from two SP services (same phase, not 2 different phases, or split phase),...What do you mean by 'all poles' - you presumably don't mean 'all 4', do you (i.e. two neutrals taken through the RCD)? Does the arrangement you're describing even work (in terms of RCD functionality)?
As I hinted before, are you sure that the cooking did not result from a poor connection at that one terminal (rather than from 'overload')?But RCD had (from looking at it) cooked from heating on one of the two live poles.
Kind Regards, John.