This rack was virtually complete and in much better condition than itís sad partner downstairs.
If any GPO engineers understand the naming (for example, the odd ZDOTR, then please write in). Most of the
metal covers remained enigmatic however, just being numbered.
"I might be able to give a little more information on some of the labelling. The room you
describe as a telephone exchange looks to be a frame room. The wiring blocks you saw are part of a
distribution frame. Distribution frames are where cables that come into a building are connected to
equipment or to cables leading elsewhere in the building. The connections are made with pieces of
wires known as jumpers."
"ZDOTR could be a site code (known as A1141 codes) showing where a cable is heading to
or it could be a piece of equipment - the letters TR often indicated a traffic recorder
in electromechanical exchanges. Cables between sites are known by their A1141 codes and
then a number (alphabetically superior first) - so for instance the second cable from
Brighton to Horsham would be the "BR-HMC No.2."
"MDF stands for Main Distribution Frame - this is the main frame in a building
and is where external cables are terminated. Other frames include RDF (used in repeater
stations where signals were amplified midway between exchanges) and IDF for Intermediate
or Internal - used within exchange floors to physically connect the different parts
of the exchange to each other."
"Essential and Non-Essential electrical circuits relate to how the building is
wired. If mains power fails non-essential circuits stop working and essential circuits
are powered by a battery back-up and a generator. The distinction between the two
is because the generators would normally not have enough power to power every
circuit in a site and/or the fuel would last longer if only certain items remain powered."