Lightning protection grounding for medical electrical equipment

- Oct 29, 2019-

Medical and diagnostic electrical equipment should be in the form of protective earthing, functional grounding, equipotential bonding or non-grounding according to the functional requirements. The operating room and rescue room should take anti-static measures as needed.

First, the classification of medical places

According to the parts and places where the contact parts are used, the medical places are divided into three categories: 1, 1, and 2, among which:

Class 0 location: A medical facility that does not use contact parts.

Class 1 location: A medical site that uses contact parts in such a way that the contact parts contact the outside of the body; except for the two types of places, the contact parts invade any part of the body.

Class 2 Location: A medical facility for contact components such as intracardiac surgery, operating rooms, and power-down critical treatments that will be life-threatening.

Second, the grounding type of the medical electrical equipment power supply system

After a sudden power outage, there are places that cause major medical risks, and should be powered by a medical IT system that is not grounded. Medical IT systems should be equipped with IT transformers and insulation monitoring devices. The IT transformer is a single transformer with a rated output capacity between 0.5 and 10 kVA.

Where medical equipment that requires protective grounding, such as a low-voltage system, is in TN form, it should be powered by TN-S system. TN-C system is strictly forbidden, and leakage current action protection device should be installed according to the following requirements:

1. In the terminal circuit with rated current not exceeding 32A in Class 1 medical facilities, the residual current action protector with the maximum residual operating current not exceeding 30mA is used as the accessory protection measure.

2. In Class 2 medical facilities, only the power supply circuit of the operating table drive mechanism, the power supply circuit of the mobile X-ray machine, the power supply circuit of large equipment with a rated power greater than 5kVA, and the power supply circuit for non-life-sustaining electrical equipment. The automatic current cutoff of the power supply is performed by using a residual current action protector whose residual operating current does not exceed 30 mA.

Third, the requirements of medical electrical equipment grounding resistance

1. The functional grounding resistance of medical electrical equipment should be determined according to the technical requirements of the equipment. Under normal circumstances, the common grounding method should be adopted. If the joint grounding body is used, the grounding resistance should be ≤1Ω. If separated from the lightning protection grounding system, the distance between the two grounding systems should not be less than 10 meters.

2. A power outlet that supplies power to a medical electrical device is a requirement for the form of the socket structure of the handheld electrical device.

3. The protective wire and grounding wire of medical electrical equipment shall be copper-core insulated wires, and the cross-sectional area shall comply with the requirements of lightning protection technical specifications.

Fourth, anti-micro shock protection measures

Devices that use medical electrical equipment that is inserted into the human body to access the heart or directly into the human heart should be protected against micro-shocks as follows:

1. It is advisable to use the equipotential bonding method to equipotentially connect the indoor water supply pipe, the metal window frame, the metal frame of the ward and the metal parts of the parts that the patient may directly or indirectly contact within 2.5 meters. The resistance value of the protection line connected to the potential should be such that the potential difference between the above metal conductors is limited to 10 mV or less.

2. Class II electrical power supply equipment should be used.

Fifth, Auxiliary equipotential bonding measures

Auxiliary equipotential bonding shall comply with the following regulations:

1. In each Class 1 and Class 2 medical facility, an auxiliary equipotential bonding conductor shall be installed and connected to the equipotential bonding busbar located in the “patient area” between the following sections:

Protective conductor

Externally conductive part

Anti-electromagnetic interference shield

Conductive board network

Metal shield of the isolation transformer

2. In each Class 2 medical facility, the resistance of the protective conductor terminal of the power outlet, the protective conductor terminal of the fixture or any externally conductive part, and the connection conductor between the equipotential bonding busbars shall not exceed 0.2 Ω.

3. The equipotential bonding busbar should be located in or near the medical facility. An additional equipotential bonding busbar shall be installed in or near each switchboard, and the auxiliary equipotential conductor and the protective earth conductor shall be connected to the busbar. The location of the connection should be such that the connector is clearly visible for easy removal.