As the link to the file related to the 21st class in the DPK classification in the web.archive.org website I had given in my previous post seems no longer work, I have added the corresponding attached file below I downloaded yesterday. The most relevant subclass in the document is "21g" in the 1953 version of the DPK.
In addition, it may be interesting to compare the three technologies involved in the Elektro-Zentral-Ges. founded in 1915.
So, the final purpose of the company might have been to develop a transmitter-receiver communication device usable for national defense and powered by the Stromerzeuger which would have used a method for concentrating electric waves which makes the stromerzeuger look like the apparatus Heinrich Hertz used in 1888 to study the propagation of the electromagnetic waves.Purpose of the company: The exploitation of the three inventions:
1) Device for concentrating electric waves (DRP registered and utility model registered),
2) Power generator (DRP registered No. 5101 - VIII and DRGM No. 591045 of February 20, 1914),
3) Device for the simultaneous use of a telephone line for more than 2 calls and its utilization for national defense
The DRGM 634869 III / 1915 (21a)-772 document related to a 21a subclass in the DPK classification may be related to the telephone-type device.