Safety in medical electrical equipment starts with the power input

Electrical equipment used in medical technology must fulfil high requirements in terms of safety. This protects both the patient and medical staff. Schurter offers a wide range of products for medical equipment, including power sockets and power entry modules with and without power-line filters as well as filters.

Medical electrical equipment has extensive requirements regarding safety defined in a base standard IEC/UL 60601-1, so as to ensure patients or medical staff are not place in danger. Schurter’s product range for use in medical electrical equipment includes power feeds, fuse holders, switches and power line filters.

Power feed: Medical devices connected by a detachable power cord must meet the requirements of Standard IEC 60320. It is also recommended to protect against unintentional removal of the plug from the power socket.

With Schurter’s V-Lock cord retaining solution the power socket is equipped with a notch that interlocks with a special latch on the connector of the power cord and prevents the cord from being pulled out of the socket unintentionally.

Fuse holders: Permanently installed medical electrical equipment comes with its own fuses. If there is a failure in a piece of equipment, a fuse prevents that unit from tripping the circuit breaker and disconnecting other, sometimes life-critical devices, from the mains. It is recommended that all medical electrical equipment be equipped with a double-pole fuse holder and that only authorized personnel can remove or replace fuses. The basic standard for medical electrical equipment, IEC/UL 60601-1, specifies fuse holders that can only be accessed with the help of a tool. For this, Schurter offers the ‘Extra-Safe’ fuse drawers.

Switches: The line switch at the power feed has an important function. Just as with fuse holders, it must be ensured that the equipment is completely disconnected from the power network after being turned off. If only one pole in a non-polarised power distribution network is interrupted, the equipment could still be live. Thus, it is preferable to use a switch that disconnects the power feed on two poles.

Power-line filters: The power-line filter protects the equipment from external HF interference and reduces the HF interference radiated by the equipment. They are often necessary in order to fulfil the EMC standards for CE declaration of conformity

Leakage currents

Capacitors in filters cause leakage currents. In medical electrical equipment these may not exceed 100 µA under normal conditions, and for devices with direct patient contact, it drops to just 10 µA. Therefore, power- line filters for medical equipment do not have any Y capacitors or only very small ones, which results in a maximum leakage current of 5 µA or 80µA.

Capacitors used are wired directly between the energized conductors (X capacitors) or between the energized conductors and earth (Y capacitors).

If the power cable is removed from the socket, the stored voltage from the X capacitors is still present on the power pins and if touched can result in an electrical shock. A bleed resistor is placed in between the phase and neutral conductors to discharge the capacitor quickly which eliminates this issue.