Phillip87

Just one thing I want to comment on, and that is the idea that RCDs don't work in non-TN earth systems (TN, terra-neutral, earth and neutral is at the same potential). RCDs are used even in IT systems (no bonding). If there is an imbalance of 30mA caused by some kind of earth fault (probably through a human being), it trips.
There are two reasons for bonding the system. One is to limit the maximum voltage. As an example, it is possible for neutral and live to both be thousands of volts above earth while still only being 230V RMS between L and N. By tying one end to earth you know the highest voltage in the system is 230VRMS and it's on the live wire.
The second reason is to help detect earth faults. With an unbonded system, the first earth fault goes unnoticed, but the second one closes the circuit and causes current to flow. By bonding the system, a single earth fault can be detected.
There are many ways of referencing a system to earth. There is even something in three-phase systems called corner-earthing, where you have a delta transformer (aka three wires, no neutral), you will tie one of the phases to earth. Again, this is to limit the maximum voltage (some part of the system corresponds to 0V) and aid in detection of earth faults.
Now note that even in unbonded systems with an undetected existing fault, an RCD still does the job. If 30mA  of current passes through a human, the RCD will still see it and trip.
Now... what's up with the V-0-V configuration? If you earth the central point, you still have some part of the system referenced to earth, the maximum voltage in the system is now 120V, and if there is a low-enough impedance path to make 30mA flow, your RCDs still trip. So on the upside, there is no reason to consider a V-0-V setup as unsafe in principle.
BUT... South African regulations does not allow you to do this in a residential setting, and your neutral wiring is also not really neutral anymore... it is a second "hot" like it would be in North America.

cut the original power supply cable install the one end to the controller and connect the other side to 12v supply that way the gate wont beep when in operation. 

The Sans Regulations supersedes the inverters installation manual, the documents state that all installs should adhere to Sans10142
 
the bonding relay would make this a non compliant installation as the regulations require a permanent earth neutral bond on the output side of an alternate supply source before it is wired to the changeover switch input.
 
Non essential/essential loads needs a separate neutral bar, the inverter must have a separate grounding rod, reason being if the changeover is switched to the inverter the Bond is broken on the utility side and effectively on all essential loads if there is no earth spike with a bond the inverter wont have a zero voltage reference.