a method for using an underground mine communication system to effect minewide communication and an intrinsically safe current limiter circuit for insuring that electrical equipment in the system will not cause incendiary conditions . the underground mine communication system comprises a plurality of repeaters and medium frequency radios , including mobile , portable and personal - carried radios , coupled to electrical conductors and natural waveguides existing in the earth by tuned loop antennas . messages transmitted by the radios are carried to the repeaters by the conductors or coal seam waves . the repeaters amplify , replicate and retransmit the message at two different frequencies for transmission of the message to a surface base station and to other radios in the system . a paging system , which has a separate set of repeaters , is also coupled to the network of electrical conductors and natural waveguides by tuned loop antennas . the paging system alerts miners to contact the surface base station . radios , pagers and repeaters in the system are equipped with the intrinsically safe current limiter circuit to preclude the development of incendiary conditions . the current limiter circuit comprises a series arrangement of a current trip circuit , a redundant current trip circuit and a current limiting field effect transistor controlled by a feedback control amplifier .