IEC 60320 Electromagnetic & Radio Frequency Interference (EMI/RFI) Filtered Inlets and Outlets

Whether an IEC 60320 hospital-grade power entry module housing up to 5 functions (e.g., inlet, voltage selector, switch, fuse, and filter), or a 2-function outlet housing a filter, the 2-5 function modules, inlets, and outlets have at least one common denominator as hospital-grade components—the EMI/RMI filter. So, whether selecting a 2, 3, 4, or 5-function module, inlet, or outlet, the EMI/RFI filters decrease electrical noise whether natural disturbances, such as lighting and solar flares, or human-made EMI, such as cell towers, power lines or interference from appliances and equipment. In essence, a filter reduces or shunts away unwanted and potentially harmful EMI/RFI that interferes with office equipment and devices, as well as larger industrial equipment.

In medical applications, filters reduce or nearly eliminate incoming noise, which may interfere with sensitive diagnostic testing equipment such as CT scanners, X-ray machines, medical-grade treadmills, and ECMO machines—moreover, noise generated in your equipment may affect other equipment directly attached to the patient. Additionally, most equipment in the patient proximity is required to limit leakage current below a specified level of 200mA. Leakage current is a type of current that is radiated onto the ground plane by surrounding electrical fields created by some of the filter’s components. Standard filters typically produce leakage current in the 2 to 5mA range; medical grade filters are specially designed to be rated in microamps (2-5µA) for leakage current demanding less leakage.

Inside an EMI Filter

Simply put, a filter provides “clean” electricity to the equipment. The circuit components in filters include inductors, resistors, and capacitors. The difference between a standard filter and a medical-grade filter is that in the medical version the capacitors between the circuit conductors have been removed as to decrease leakage current values. Also, the arrangement of inductors, capacitors, and resistors play a vital role in decreasing unwanted EMI as it is shunted away to ground. This is especially important in equipment where leakage current values are tightly controlled by country-specific or international safety standards as to ensure patient safety.

Interpower^® filtered power entry modules are available with or without a metal shield, which is typically used in high-frequency applications. Whenever specifying a module with a filter, it is beneficial for a company to obtain samples of filters to test within their applications to ensure they will perform to expected current values. This is due to filter performance specifications being based on an industry standard 50-ohm test circuit, and certain aspects of an application’s design may alter the way a filter performs when the circuits are connected.

One way to reduce EMI/RFI is to avoid using longer electrical cords which tend to have antennalike qualities, attracting wavelengths of certain signals.

“In regard to medical equipment,” said Dan Ford, Interpower Technical Support Specialist, “if you go beyond the 12–15 feet length for medical cords, it becomes much more difficult to meet the equipment standard requirements for resistance and leakage current for the entire system. You don’t want high levels of EMI/RFI in equipment attached to the patient.” Another overlooked factor is the calculation of cord length in electrical designs; too many cords bearing multiple copper wire conductors can inhibit the EMI/RMI filter you’re using.

Voltage Drop & Cord Length Calculation

Understanding cord calculation and voltage drop are crucial for your electrical design. In this white paper, you will discover the inherent dangers in long cable lengths, learn the maximum percentage your cable can be derated and still meet UL and CSA requirements, and get the tools you need to calculate voltage drop for the cords in your electrical designs.

Additional Resources

For more information on filtered inlets and outlets, please visit Interpower’s IEC 60320 page at IEC 60320 Inlets & Outlets