Overload protection

MrJack96: 
Am I right in saying this is the same for if you was tapping of a bus bar the overload protection may be downstream so the conductors should be sized to the downstream circuit as long as Fault protection ADS upstream of the cable is in place and the ZS of the cable is met? 

Not quite the same in my view.

Small conductors tapped off large busbars MIGHT not even be protected against short circuit, this is permissible for SHORT conductors that are physically protected against damage.

For example, a SHORT length of say 6mm that connects a 32 amp switchfuse to a 315 amp busbar.  In such a case my preference would be for a larger capacity switchfuse, perhaps 100 amps, with terminals that accept say 50mm cable. 50mm is probably protected against short circuit by the upstream 315 amp fuses.

Also acceptable for SHORT conductors that connect batteries, transformers or generators to control panels or other equipment that incorporates OCPD. 

What the O/P is proposing is a cable that IS protected against short circuit by the upstream device, but is NOT protected against overload by any upstream device. Reliance being placed upon the downstream devices for overload protection. Acceptable but poor practice in my view.

MrJack96: 
Am I right in saying this is the same for if you was tapping of a bus bar the overload protection may be downstream so the conductors should be sized to the downstream circuit as long as Fault protection ADS upstream of the cable is in place and the ZS of the cable is met? 

Not quite the same in my view.

Small conductors tapped off large busbars MIGHT not even be protected against short circuit, this is permissible for SHORT conductors that are physically protected against damage.

For example, a SHORT length of say 6mm that connects a 32 amp switchfuse to a 315 amp busbar.  In such a case my preference would be for a larger capacity switchfuse, perhaps 100 amps, with terminals that accept say 50mm cable. 50mm is probably protected against short circuit by the upstream 315 amp fuses.

Also acceptable for SHORT conductors that connect batteries, transformers or generators to control panels or other equipment that incorporates OCPD. 

What the O/P is proposing is a cable that IS protected against short circuit by the upstream device, but is NOT protected against overload by any upstream device. Reliance being placed upon the downstream devices for overload protection. Acceptable but poor practice in my view.