More questions about transformers.

The practice of earth grounding a secondary is commonly done where say a high voltage supply transformer is used for a local 120v control circuit as in industrial machines etc, once you isolate by this method, the earth grounded neutral is lost, so it is customary to connect one leg of the secondary to the service ground, right at the transformer, these two conductors are now used as earth ground and local neutral conductor in the usual way.
Incidentally this is done at your residential service entry where the transformer centre tap is connected to earth ground and then constitutes a neutral conductor.
M.

 

Often confusion follows when talking about Earth and Neutral.
Instead of calling it a Neutral, think of it as "The other current carrying conductor", or "return current conductor".
An Earth Ground or Bonding wire is only intended to carry " fault current" , and we don't want " fault currents".

When a green ground wire is attached to a chassis, it only purpose is to provide a path to Earth ground if another "Live conductor" should accidently make connection with the chassis. In this case the chassis potential is Zero and if your body provides a path to ground when you touch the chassis, the green ground wire will provide the lowest resistance path to ground and(not though your body)

Assuming residential wiring in the US: The black (120V) wire is the feed, and the white (sometimes called the neutral), is the return current carrying conductor. Back at the Service Entrance box the Whites and ground terminals are bonded (and only here are they connected). Since the return wire (white) carries load current, and has resistance, it can and will develop a voltage drop. Depending on the load current, the drop can be quite high, and thus a shock hazard from the so called neutral wire.

Grounding at the Service Entrance point assures a direct connection to ground, with the lowest voltage drop.

 

Keep in mind that after rectification and capacitor smoothing the resultant DC voltage will be 1.414 x the applied AC.
M.

 

Largely the confusion arises in N.A. because of the terminology of using 'Ground' as a term for P.S. common, system common and for earth ground.
Even schematics show an earth ground symbol whether common is Earthed or not.
For countries such as the UK, the term 'Earth' is used if referring to an earth grounded conductor.
M.

 

Note that the 12.3V is AC.
Show on the pic where exactly do you connect the capacitor?

 

The circuit you have drawn doesn't agree with the schematics.
The schematics looks rather strange though.
The transformer secondary voltage should be 2x6.3+12.3=24.9Vac,
you can check that.
Why do you need to add a captor anyways?