Additional device is a telecommunications term from the time of the Reichspost and the Deutsche Bundespost for devices that were not part of the standard equipment of a telephone connection. In addition to the telephone, they could be electrically connected to the telephone line .
Additional equipment were z. B .:
- Junction boxes
- Second earphone and telephone receiver
- Second alarm clock
- Heavy current switch relay
- Fee indicator
- additional telephones
- Answering machine
- Toggle switch
- Automatic changeover switch
According to the technical operation of the additional equipment, the following groups were distinguished:
- Group A (ZPrA)
- Devices that have been connected in terms of circuitry in front of the telephone, e.g. B. Dialers.
- Group B (ZPrB)
- Devices that have been connected to the telephone in terms of circuitry , e.g. B. answering machine.
- Group C (ZPrC)
- Devices that are connected like a second receiver (on the telephone), e.g. B. Loudspeaker devices.
The connection of additional devices of groups A and B took place e.g. B. via an eight-pin junction box (ADo 8).
Furthermore, there was a distinction between "own", "participant" and "private".
- Post's own additional facilities
- were rented and installed and maintained by the Deutsche Bundespost.
- Participant's own additional facilities
- the customer bought from the Bundespost, which then installed and maintained it.
- Private additional facilities
- the customer could buy on the open market, but had to have it installed by the Deutsche Bundespost. The customer was responsible for maintenance.
Private additional facility
If an additional device submitted for examination did not appear suitable for official introduction, it could be approved as a private additional device ( ZPr ). Only devices approved by the Deutsche Bundespost were allowed to be switched on as ZPr. Examples of additional private facilities are:
- Answering machine
- High voltage alarm clock
- Flash lamps
- Fax machines
- Reichsgesetzblatt of August 30, 1921: The telephone order. 25 August 1921.
- Federal Law May 14, 1971: Announcement of the telecommunications regulations .
- Handbook of Telecommunications, Basic Series Volume 6, Telephones - Telephony Suppression - Private Branch Exchange 5th Edition, 1976, p. 55
- Kurt Hantsche: Pocket book of telephone extension systems. 2nd edition, Verlag R. Oldenbourg, Munich 1964, p. 227