Crane jib protection equipment from overhead cable - comprises aerial assuming potential to earth on approaching cable

摘要

The equipment prevents crane jibs, the booms of concrete pumps etc. from approaching too closely to high-tension overhead cables when working near them. It comprises an aerial mounted on the jib etc. or the jib itself can act as an aerial. On approaching the overhead line the aerial assumes a potential to earth commensurate with the intervening distance. This potential can be applied to the input of a high-resistance switching circuit, whose sensitivity can be preset. The circuit in turn can actuate a relay to stop any movement initiated by the control switch, after which only movement in the opposite direction is possible, an alarm signal, being given at the same time.