C of A
General Information:
What we call Australia, is officially the Commonwealth of Australia (C of A). It consists of 6 states: New South Wales, Queensland, South Australia, Tasmania, Victoria and Western Autralia. In addition 3 territories: ACT (Australian Capital Territory), Jervis Bay and the Northern Territory.
The total population is about 22 million people.

The majority of the "Z"-plates shown here, were used from 1961 to date. The first issues had a plain white base, from 1972 the base was reflective white.
Plates in my collection:
C of A

Federal Government / Minister from WA
801-850 = allocated to Western Australia
From 1993
Series ZAA-ZAZ = Transport (Aviation) Department / F = Federal, only required in Western Australia, because of insurance regulations.

From 1979
Series ZBA-ZBZ = Northern Australia Department (till 1983)
ZBA-ZBZ = General series (from 1983)
Series ZEA-ZHZ = Federal Telecommunication Department
No legend at the top.

From 1979
Series ZMA-ZMZ = Snowy Mountains Authority
Series ZNA-ZNZ = Dept. of Defense (Navy) Hydroelectric Authority

From 1979
Series ZPA-ZPZ = Postal Commission
From 1979
Series ZQA-ZQZ = Administrative Services

Series ZSA-ZSZ = Administrative Services
From 1979
Series ZUA-ZUP = Administrative Services

From 1979
Series ZXA-ZXZ = Trailer of all departments
From 1979
Series ZWA-ZWZ = Housing & Construction Department

Defence Centre - Canberra
Used on busses shuttling between the Defence Department Complexes and the Civic Centre
Asset Services / Total Building Maintenance
A = Indication of the state (A is unknown to me)