Are we implementing a Protective-Neutral-Bonding system with high protective conductor current equipment?

摘要

As a by-product of harmonic distortion, for the majority of Information Technology and energy saving equipment, circuit-protective-conductors are seen to be carrying a significant earth leakage current even when the circuit has no fault. From BS EN 60479, it was assumed that a threshold of 'let go current' is approximately 10mA for some form of electric shock sensation. BS7671:2001 requires equipment with a high protective conductor current that exceeds 10mA to have a high integrity duplicate circuit-protective-conductor connecting it to an independent earth termination point or, the alternative is, to use an isolation transformer to supply the equipment. In this paper, the results of earth leakage current measurements carried out and the observed waveforms for a typical set of office equipment were being examined. In this paper, the earth leakage current measurements and waveforms obtained for a typical set of office equipment were analyzed. Based these measurements, it is concluded that equipment with high protective conductor current should be given a dedicated fourth conductor to conduct its high protective conductor current without contaminating the circuit-protective-conductor. This conclusion, if conies true, no doubt has impact to our engineering practice.