Contact at Plate - FED

[bwbuddy]

(FED) What guidelines should be used when calling a runner out at home for making contact with the catcher? When should contact be considered incidental? What if the catcher was up the line 2 feet without possession of the ball? What if he drops the ball? Should contact significant enough to knock the catcher over always be called an out even if, in the umpire's judgement, the contact was accidental or unintentional?

I've seen this called so many different ways - obviously, parents and coaches' perceptions of the way it should be called is always different based on whether our team is on offense or defense.