Earthing?

[Neale]

OK, I'll kick off but there will be plenty of opinions given to this list of questions! One point to remember is that sometimes you earth for electrical safety and sometimes for screening/electrical noise reduction. Good earthing practice via star point will generally address both concerns.

Metal case - shielding comes for free that way. You will probably need a bigger box than you thought, and not sure about strength of larger plastic boxes.

Driver enclosure is isolated from all internal electronics so doesn't matter whether it's connected to ground or not. Bolting an anodised enclosure to, say, an epoxy-coated steel box might or might not give a decent electrical connection but I wouldn't worry about it myself. I didn't in my own control box.

I reckon that anything that has mains going in should be earthed, so if your PSU doesn't have a connection for mains earth, then the case should probably be earthed (via a wire to a mounting bolt? See comments about bolting to epoxy-coated steel) anyway, and that would go to the star point, where the mains earth is also connected.

My first router was built from MDF so the spindle motor (usual 2.2KW water-cooled) was isolated from ground. Under certain circumstances, you could feel a slight tingle from it when you touched it while running, which was some kind of electrostatic or electromagnetic leakage from the power feed to it. Not dangerous but mildly inconvenient. Decent earth connection immediately stops this kind of thing. Also, if you are going to use a touchplate for tool height setting, the spindle must be earthed. It might be that your mill builder took a belt-and-braces approach to earthing, but it might be because it's better to avoid relying on a metal-metal contact in sliding surfaces which, theoretically, are held apart by a tiny layer of lubricant. My new all-steel router uses earth wires running through the various cable chains to make sure that there is an earth wire between all pairs of moving parts to avoid relying on contact via the profile rails and bearings. Like that, there is a solid electrical earth run from spindle platform right back to the main router frame which is in turn earthed inside the control box by a wire from a mounting bolt back to the star point.

I use a 10A (I think) MCB in the control box as the mains enters. It's not clear to me what use further fuses are as any average electronic item will blow in a thousandth of the time it takes a fuse to react; fuses do not protect electronics, faulty electronics blow fuses (occasionally). Fuses sit there saying, "I wonder where all that magic smoke is coming from? Good job I'm still working!" Primarily, they might stop a fire if there is a major wiring fault causing a sufficiently high current short.

One man's view...