UAX13 exchanges were used extensively in New Zealand to provide automatic telephone service in the rural areas. There were some changes to the standard design and so were re-designated UAX NZ13 because of this. The changes were minor and were mainly labeling because of New Zealand’s reverse number dials.
The "R" unit (UAX NZ13R) was used to provide multi-party rural automatic lines in the more remote areas and provided both five party and ten party lines. The three digit phone numbers all started with the digit "5". The code rings used on the party lines used were 'X' 'A' 'D' 'J' & ' K' for group 1 lines (50x, 51x, 52x, 53x, 54x) and the 'M' 'R' 'S' 'U' & 'W' codes were used on the group 2 lines (55x, 56x, 57x, 58x, 59x). This allowed a group 1 line and a group 2 line to be combined into a single ten party line by re-jumpering on the final selector terminal strip.
The telephones were equipped with a rotary dial, a generator handle and a push button for automatic use.
The "R" unit was a double-sided rack with equipment mounted in both the front and back. It could be installed remotely from the parent UAX as well being co-located in the same building as it was a completely self contained unit with junction circuits connecting it to the parent UAX. On the front side (see photo) it was equipped with subscriber line circuits, the number side of the MDF, discriminating selectors and final selectors. At the rear, it was equipped with the cable side of the MDF, a multi party code ringing generator unit and both incoming and outgoing junction relay sets.
If a subscriber wanted to call another number on the same line as them, they just cranked the generator handle to create the appropriate code ring. After doing this several times, they would then wait for the other party to answer.
For an automatic call to another number on the UAX or beyond, the subscriber pushed the button on the phone to get dial tone. A free linefinder associated with a discriminating selector hunted for the calling line. Once the calling line had been found, the discriminating selector hunted for a free junction to the parent UAX, seized the junction and Dial Tone was returned to the subscriber from the parent UAX equipment. After the initial digit was dialled the discriminating selector determined if the call was a local call to a subscriber on the R-unit or a call to the parent UAX.
If the first digit for a local call was dialled (usually '5') the junction to the parent UAX was released and the discriminating selector hunted for a free final selector and when one was found extended the calling subscriber to the final selector. The next two digits were dialled into the final selector. If the called line was not in use, coded ringing was sent to the called subscriber. To answer an automatic call, the called subscriber picked up the handset and then pressed the button.
If the call had been for
the parent UAX then the discriminating
selector would continue to repeat the digits dialled via the junction to the parent UAX.
There was also a "blind" junction position on the discriminating selector which allowed a local call to be completed even when all junctions to the parent UAX were busy.