Discussion on grounding system in hospital electri

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Discussion on grounding system in hospital electrical design Abstract: since TN-C system is not allowed to be used in hospital electrical design, TN-S grounding system or it grounding system can be used according to different functions of internal rooms in hospital buildings; Local equipotential measures should also be taken for operating rooms with high risk of electric shock

key words: TN-S system it system local equipotential bonding micro electric shock Untitled Document with the development of modern medical science and technology, more and more medical electrical equipment and medical electronic instruments are widely used in hospital clinical diagnosis and treatment, such as ect, CT, NMR, etc. With the introduction of technology and new equipment, there are many problems to be paid attention to in the hospital electrical design, and the electrical grounding problem is a reliable guarantee for the hospital electrical safety

1 selection of grounding system

TN-C grounding system is not allowed to be used in the medical places of the hospital and its associated places, because unbalanced current or single-phase load current will flow on the pen line during normal operation of this system, and this current will cause voltage drop on the pen line, thus the medical electrical equipment shell will also have a voltage to the ground. In addition, TN-C system will also bring electromagnetic interference to medical electrical equipment, which can be avoided by using tn-s. It system should be used in the local scope of the operating room

2 application of TN-S system in medical buildings

article of code for electrical design of civil buildings JGJ/t16-92 (hereinafter referred to as "Civil Code") stipulates that "for medical equipment requiring protective grounding, if the low-voltage system is TN type, TN-S system shall be used for power supply", The medical electrical equipment in direct contact with the human body (except that the oil output from the first-aid and surgical electric oil pump enters the oil cylinder equipment first) shall be equipped with leakage current action protection devices. All medical electrical equipment with conductive shell height less than 2.50M, whether fixed or hand-held, shall be equipped with leakage protector (RCD). The over-current protection appliance for short circuit and overload should not use fuse, but low-voltage circuit breaker

3 special requirements of the operating room. Therefore, the mechanical properties of the materials are not described in this paper. Under the general electric shock, the charged conductor contacts the human skin. Only a few people are familiar with the technical indicators, use methods and operation specifications of the equipment, which pass through the heart. Therefore, the total current passing through the human body does not exceed 30 μ A. There will be no death due to ventricular fibrillation. If the current passes directly through the heart, the current exceeds 50 μ A is at risk of death from ventricular fibrillation. IEC standard stipulates that the normal state of leakage current allowed by medical equipment through the patient's heart is 10 μ Below a, single fault status is 50 μ Below a, the potential in the operating room is 10mV when it is normal, and the single fault state is 50mV. Therefore, leakage current action protection should not be adopted for special medical equipment, but protection measures to prevent micro electric shock should be taken

according to of the regulations, after the sudden interruption of current, the ungrounded (IT system) power supply mode of power system shall be adopted in places that may cause major medical risks. A special isolation transformer shall be set for this power supply mode, and the power supply of IT system shall be led out from the secondary of the isolation transformer to prevent the generation of grounding fault current. The IT system is introduced into the operating room and emergency room, and a distribution box is set in the room, which is commonly referred to as PA in foreign countries. A set of leakage detection device (insulation monitoring device) is set in the process automation, and a fault alarm is sent out in case of single-phase grounding fault (generally when the system insulation level is lower than 0.5m Ω). When a single-phase ground fault occurs, the fault current is only a small amount of capacitance and current to the ground of a small section of line in the medical place, resulting in a small potential difference in different parts of the place. The operation can be continued without cutting off the power supply on the premise of ensuring the safety of the patient

4 make local equipotential bonding

in order to prevent micro electric shock, adopt equipotential grounding and use class II electrical equipment (i.e. electrical equipment with double insulation or reinforced insulation). Equipotential bonding against micro electric shock shall include indoor water supply pipe, metal window frame, metal frame of hospital bed and various metal parts that patients may directly or indirectly contact within 2.5m. The resistance value of the protective wire used for equipotential bonding of the above components shall make the potential difference between the above metal conductors less than 10mV. Equipotential bonding box can be set on the wall of the room, and the equipotential bonding plate in the box is connected with the equipotential bonding trunk line. The local equipotential bonding in the IT system shall not have any path connection with the PE line of the TN system. The specific methods can be as follows: make an insulating layer on the structural plate, and then make a fine aggregate concrete cushion on it, with an internal length of 100m × 100m laying Φ 4. The reinforcement steel forms pressure equalization, which is used at two places of the pressure equalization diagonal Φ 12 galvanized round steel shall be used as an adapter box 30cm above the ground, and then connected to the local equipotential bonding terminal board with bvr-25 copper conductor. No metal pipeline of TN system shall be laid in the grading cushion. References: [ 1 ] Wang Houyu. Safety of hospital electrical design [ J ]. Building electrical, 1993, (4). Journal of Jiangxi Electric Power Vocational and Technical College

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