solid vs stranded wire - also grounding conductor connection
As always, thanks for your forum. Here are a few items I have not seen addressed as I look through the archives, nor in books I've picked up.
Are there restrictions on using solid vs stranded wire (or both together) for branch circuit wiring (12 or 14 ga 20 or 15A circuits)?
Is it ok to mix solid and stranded wire in "wire nut" connections? The boxes connectors come in usually state the acceptable gauges and numbers of conductors but have nothing about solid/stranded.
Is it ok to put a stranded wire on a screw terminal (e.g. on a receptacle) which would normally take solid wire, if the stranded wire is first tinned? The alternative would be to put a solid pigtail on the stranded wire (with a wire-nut) and connect the solid to the screw.
Are there some types of terminals which should not have stranded wire attached - in my service panel is a neutral bus bar where the neutral wire is inserted through a hole and compressed with a screw. It looks like a stranded wire could fan out and not stay tight in place under the screw - is this a concern? Service panel mfrs web info did not address this.
Regarding the use of separate grounding conductors (green or bare), I assume that a receptacle, fixture, etc. should always be grounded to a box with some kind of pigtail (so grounding continuity does not depend on the mounting screws). But if wiring to the box is run in metal raceway (EMT or flexible "fixture whip"), is that sufficient to complete the ground to the box (in dry or possibly damp locations, not wet)? Do I ever need to run a separate green grounding conductor through the entire raceway from the service panel or other ground point? Would this be recommendable under some conditions?
Finally, when connecting a green or bare grounding conductor to a box by means of a green tapped screw, should this connection be made with a crimp lug or something which would prevent the wire from moving out from under the screw head? This could happen easier with stranded wire. Unlike most screw terminals on receptacles, busbars, etc, there is nothing inside a typical junction box to corral the wire into place under a ground screw.
These questions are partly motivated by my trying to upgrade and standardize wiring in my old house where original wiring seems ok but I have found numerous loose/uncertain "repaired" connections which seem likely to promote arc faults.