The ARJ03 are junction boxes used for expansion of the APM databus. It allows to connect multiple APM consoles on the databus, containing a "BUS IN", "BUS OUT" and a "TO APM" connector. When using large cable lengths, the voltage distributed by the databus becomes insufficient and an additional voltage need to be applied. The ARJ03P has to be used when cable lenghts are longer than 100 m.