Question 1
Electrical safety testing involves the measuring of electrical circuits and appliances to ensure that they adhere to the set national safety standards. Electrical safety testing is important because it ensures the safety of end-users, detect defects and prevent faulty components from being installed, facilitate cost control, and prevent product liability suits (Ghosh et al., 2015). The installation of appliances within the patient care area must adhere to the leakage current limit of 300 µA, and resistance of less than 0.15 ohm between the appliance chassis and the ground pin of the attachment plug (National Fire Protection Association, 2012).
The need for an electrical safety test is depended on the condition of protective earth continuity, insulation, and current leakages; if there is a probability of an electric shock during usage, such devices need electrical safety test. Devices’ testing procedures are dependent on their categorization into Class I, Class II, and Class III equipment. Class I appliances have protective earth (Davies, 2019). The electrical safety of Class I devices starts by exploring its basic means of protection, which is the insulation between live parts and any exposed conductive parts. Its supplementary protection, which is the protective earth, is then evaluated- fuses at the end of the device’s end show are evaluated to confirm its ability to break circuit when the faulty current goes through the protective earth (Davies, 2019). Class II appliances use double insulation or reinforced insulation. The evaluation of Class II devices involves the analysis of the integrity of its insulation (Davies, 2019). Finally, in Class III appliances, protection against electric shock depends on the idea that no voltage higher than the allowable safety extra-low voltage (SELV), that is, voltage not higher than 25V alternating current, or 60V direct current, exist (Davies, 2019). The current IEC standards related to patient safety against medical appliances does not recognize Class III equipment because limitation voltage is not considered adequate to ensure patient safety. However, if these appliances are connected to the main, its safety must be tested as Class I or Class II, accordingly.
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Question 2
According to NFPA 99, wet locations are areas in a patient care area where procedures performed are subject to wet conditions while patients are presents. Protection against electric shock can be achieved through:
A power distribution system that innately limits the probable ground-fault current as a result of the first fault to a low value, without disrupting the power supply (National Fire Protection Association, 2012).
A power distribution system where the power supply is disrupted when the ground-fault current gets higher than 6 mA (National Fire Protection Association, 2012).
Question 3
The leakage current for these appliances should not exceed 500 µA when they are used in a patient care area, and when they will contact patients when in use (National Fire Protection Association, 2012). nonpatient appliances without a grounding conductor in their power cords shall not be allowed within the patient care vicinity. If these appliances are double-insulated, they can be located within the patient care area.
Question 4
Ideally, ampacity consideration guides the selection for short wire length, that is less than 50 feet. Therefore, if the power code is 18 feet, and the maximum allowable resistance between the appliance chassis and the ground pin of the attachment plug is 0.15 ohms, ohm/feet will be (EDN, 2013):
= 0.0083 ohm/ft = 8.3 ohms/1000 feet.
Therefore, based on the American Wire Gauge (AWG) size and property chart, a 19- gauge wire should be used on the power cord if the maximum resistance of 8.3 ohms/feet is not to be exceeded.
Question 5
Multistrip outlets are designed for small wattage electrical devices, with the outlets required to have a three-pronged plug with a fuse or a circuit breaker. Besides, the appliances must be plugged into a properly grounded wall outlet (Burgess, 2019). Amperes should not be high than 16 amps, on a 20-amp circuit. Therefore, the voltage requirement of the three devices must be analyzed to ensure that it does not exceed the required limit.
References
EDN. (2013). What size and type of output wire should I use? edn.com. https://www.edn.com/what-size-and-type-of-output-wires-should-i-use/
Burgess, R. C. (2019). Electrical safety. Handbook of clinical neurology , 160 , 67-81.
Ghosh, C. M., Basak, R., Ghosh, A., Balow, W., & Dey A. (2015). An article on electric safety. International Journal for Scientific Research & Development, 3 (10), 503-506.
National Fire Protection Association. (2012). NFPA 99-Standard for Health Care Facilities Code-Tentative Interim Amendment. Quincy, MA: NFPA .
Davies, H. (2019). Classes and types of medical electrical equipment. Retrieved 17 February 2021, from https://www.ebme.co.uk/articles/electrical-safety/classes-and-types-of-medical-electrical-equipment
