One MOPP or Two? Select a Medical Power Supply That Prevents Shock

Medical equipment designers have to not only make sure their device performs as intended but also do so without compromising the safety of the patient or operator. Electrical shock is an important safety hazard in medical equipment, and design requirements that address it are strict by necessity. To mitigate shock and other safety risks, power supplies must comply to International Electrotechnical Commission (IEC) 60601-1 3rd edition medical equipment standards pertaining to isolation voltage, leakage current and creepage/clearance distances. This blog will review two of the many safety categories to remember when selecting a power supply for medical devices.

Under the IEC 60601-1 safety standard, proper creepage and clearance distances help power supplies achieve sufficient isolation protection between the electrical circuits and equipment that may contact the device.

Isolation and Insulation Requirements

Patients can be potentially vulnerable to electric shock when they come in contact with, or come in close proximity to certain medical devices. IEC 60601-1 3rd edition standards for isolation between circuits within the medical power supplies include AC input, internal high-voltage stages and DC output. Isolation is accomplished using either double insulation or reinforced insulation. (Shock prevention in Class I electrical equipment only calls for basic insulation and uses protective earth grounding methods.)

Within IEC 60601-1 3rd edition, isolation protection can be classified as MOOP (means of operator protection), which means the device doesn't have to come into contact with a patient, or MOPP (means of patient protection) in which contact is required. For medical power supplies, the insulation criteria for MOOP or MOPP protection are: one layer of insulation at 240V AC requires a test voltage of 1500 V ac; MOOP requires 2.5 mm of creepage, and MOPP requires 4 mm of creepage.

However, advances in power supply technology allow for an even higher grade of safety. When choosing a medical power supply, consider manufacturers that offer two means of patient protection for devices requiring MOOP or MOPP safety. 2MOPP classified power sources at 240 V AC require a test voltage 4000 V AC and 8 mm of creepage. Supplies that meet these highly stringent 2MOPP requirements not only offer optimal patient shock protection but also help ease the end product approval process in a broad range of medical products.

Medical device designers should work closely with the power supply manufacturer to determine the shock protection they need while also considering other safety and performance factors. Not all power supplies adhere to the values spelled out in IEC 60601-1 3rd edition. Polytron's medical power supplies meet or exceed IEC 60601-1 requirements and offer 2MOPP protection. When combined with their very low leakage current characteristics, they can be an ideal choice for medical devices that contact operators or patients.

For more information, download our white paper, Selecting Power Supplies for Medical Equipment Designs.