The point is simply that they serve different purposes.
Basically in "household" the "Ground wire" is intended to provide a lower resistance circuit than the human body to the earth. That's it.
"Neutral" is in housing intended as "zero", the reference ( for systems with more then 2 wires especially).
While idealy both should be on the same potential this is often not the case. simply use a multimeter and measure the difference between your ground wire and neutral will almost always give some kind of potential differential in any building .
The
last thing you want to start doing is attaching "ground" and "Neutral" everywhere
To get back to your PS Q.
An Iron cage has a few advantages, beeing an excellent shield (less noise to pick up) , better heat conductor of you can get away with using an internal heatsink (can be disadvantage also - you don't want to heat up your PCB's
).
That it's inherent "safer" is simply not true. It all depends on the mechanical construction (metal or not).
Simply put, anything metal that MAY conduct "mains" but is not "ground/zero" of the DC circuit needs to be grounded - with an iron cage this is typically then whole cage, with a plastic cage this is almost nothing.
This does not mean you need to "ground" the "zero" of your PS *after* the transformer. Some PS have a "ground" socket on the front (to use for shielding or so) but this is *not* connected to the "zero/ground" of your PS DC output.
With a metal case you need to be especially carefull to not cause any shortcircuits trough the connectors of the DC output or the heatsink.
Things you want to do are mainly common sense:
* make sure your mains is properly fused.
* make sure the mains cables to the transformer are not to long but also not under "mechanical stress" (to short), decently secured from moving using plastic wraps and any soldering/blank metal carrying mains is isolated using heat shrink tubes.
* if you have holes where you can stick things like screwdrivers in, then make sure those cannot reach any blank metal carrying mains (see pervious point).
* if you are using and old style Laminated steel transformator (use
Toroidal core ones they are a bit more $$ but worth it) that has those hughe metal casing/square thing and it has a "ground tap" then connect that or ground it using the screws used to secure it in place.
* make sure your mains is properly fused .
* keep mains and low voltage way from each other - not only about safety, more about not putting 50/60hz noise in your cables/Dc output.
* use oversized copper wires (2.5 ² mm or so "electrical wires") to connect the DC outputs of the PS to the PCB never hurts. you don't want to loose voltage over a silly cable.
* make sure the heatsink (this is normally put externally ) is electrically shielded from the backend of power fet's/transistors using mica (and use heat paste). You can ground it but don't loose your sleep over it if you don't.
* make sure your mains is properly fused .
* use a decent mains on off switch properly reachable (not at the back..) - if things start smoking in your setup you want to get there
fast..
* make sure the pcb's and any cables are decently secured.
* connect the amp and volt meters (you did considered to put a pair in the case did you?) as close as possible to the ouput clamps.
just all IMHO of course, additions/critic welcome
ha and did I mention you need to properly fuse your mains?