Technical Articles: A technical article is an editorial for a magazine or an internet benefit that's about a specialized point, and regularly the article drills down into a few low-level of detail. May be computers, maybe material science or chemistry or any other science.
Generally, the useful life of power system components heavily depends upon the level of care given to them and their duty cycles. For example, a circuit breaker on mainly switching.
This technical article analyzes the safety requirements against indirect contact employed in particularly special medical locations (e.g., hospitals, medical, and dental practices, etc.), where environmental conditions may increase the risk of indirect contact and therefore the electroshock, precisely microshock.
Generally speaking, special locations and installations are locations where the presence of water or moisture decreases the resistance-to-ground of the person’s body by lowering his/her skin resistance. Special locations in terms of safety requirements against indirect contact are also wet locations where the humidity can increase the failure rate of equipment by compromising the integrity of its basic insulation.
In medical locations (e.g., hospitals, medical, and dental practices, etc.), patients are exposed to increased hazard of electric shock due to their particular conditions. Patients, in fact, may be unconscious, or anaesthetized and, therefore, unable to let-go of an energized part.
Medical electronics equipment may be sensitive to electromagnetic interferences irradiated by “disturbing” loads. For this reason, radio frequency input filters constituted by capacitors connected between supply conductors and enclosures of equipment are employed to enhance the electronic systems’ immunity.
Such filters may cause continuous leakage currents through the protective conductors in excess of 3.5 A. See Figure 1.
Figure 1 – Earth leakage currents due to radio frequency filters
Figure 1 – Earth leakage currents due to radio frequency filters
IEC 60950-13 limits the maximum value of leakage currents of Class I, stationary, or pluggable, equipment to 5% of the input current. The presence of high currents on protective conductors might cause nuisance trippings of RCDs, when their residual settings are exceeded even in the absence of ground faults.
Serious hazard is caused by the accidental loss of the protective conductor serving the equipment.
See Figure 2.
Figure 2 – Hazardous situation caused by the accidental loss of the PE
Figure 2 – Hazardous situation caused by the accidental loss of the PE
The leakage current, in fact, will circulate through the person’s body if she/he comes into contact with the enclosure. Thus, for safety reasons, the bonding of high leakage current equipment must be assured by enhancing the reliability of the PE. This can be obtained by doubling its cross-sectional area, with respect to minimum permissible values, by using more than one PE conductor in parallel, and/or monitoring its electrical continuity.
In addition, patients may be connected to medical equipment either through applied parts to the skin (e.g., sensors, electrodes, etc.), often locally treated to lower its resistance, and/or through the introduction of catheters directly into their body’s organs (e.g., the heart).
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