To ensure the safety of patients and medical professionals, medical electrical equipment is strictly regulated by standards and requirements for product testing.
As a primary power source for these electrical devices, medical power supplies, both AC/DC and DC/DC converters–must also comply with these standards so that the medical equipment functions within safety guidelines. This article looks at several of these standards and how to comply with them.
IEC standards
One of the standards for medical electrical devices is the International Electrotechnical Commission‘s IEC 60601-1-1 and 60601-1-2.
They define the general requirements for basic safety and essential EMC performance of the medical system, ensuring that no single electrical, mechanical, or functional failure will pose a risk to patients and/or operators.
International standards
IEC 60601-1-1 (general requirements for safety) is currently in its third edition
For nearly four decades, this standard has driven medical device innovation. Over the years, there have been revisions, additions, and amendments to keep pace with the evolving needs of the industry, so IEC 60601-1-1 (general requirements for safety) is currently in its third edition and IEC 60601-1-2 (electromagnetic (EMC) disturbances) is currently in its fourth edition.
Internationally, there are near-identical versions of the IEC standard including the European EN 60601-1, the US ANSI/AAMI ES60601, and Canadian CSA 60601-1.
Medical Power Supply Safety and Protection: MOPP vs. MOOP
IEC 60601-1 focuses on the safety of operating personnel and patients.
Although the main safety requirement in medical power supplies is safe isolation between any hazardous voltages and the patient and/or medical staff, the levels of protection required are slightly different based on either Means of Patient Protection (MOPP) and Means of Operator Protection (MOOP), with MOPP being slightly more stringent.
IEC-60601-1
The clearance separations are increased, as well as the creepage separation
IEC-60601-1 defines minimum requirements in terms of isolation voltage, creepage distance, and insulation level to protect the operators or patients from electrical shock due to a single failure condition, meaning that two means of protection (2MOPP or 2MOOP) are required in a single insulation barrier, or two single MOP systems needs to be used in series so that if one fails, protection is still provided by the other.
The clearance separations (distance through air between the two conductors) are increased, as well as the creepage separation (distance along the surface between two conductors), to ensure that there is no arc-over or short-circuiting from one conductor to another occurs in case of contamination such as dirt, dust or moisture. Table 1 below summarizes the requirements for both MOOP and MOPP as defined in the IEC 60601-1 standard’s third edition.
Operator and patient protection
For operator protection (1MOOP), one layer of insulation with a creepage distance of 2.5mm and 1500VAC of isolation is satisfactory. 2MOOP implies a double layer of insulation with double the creepage distance and isolation.
Basic patient protection (1MOPP) requires a single layer of insulation with 1500VAC of isolation and a 4mm creepage distance. The more stringent 2MOPP patient protection requires two layers of insulation for 4000VAC of isolation, and 8mm creepage distance.
Breaking Down Body Contacts and Leakage Current
Since electric current passing through the body can interfere with the heartbeat, in the worst-case scenario resulting in serious or even fatal consequences, there are strict requirements for leakage current from a medical power supply, both for current flowing from the power supply output into an earthed patient and from a earth-separated patient being earthed via the power supply output.
However, the limits depend on the kind of body contact with the equipment:
- Type B (body): contact with an earthed patient.
- Type BF (body floating): contact with a non-earthed patient.
- Type CF (cardiac floating): contact with the heart of a non-earthed patient.
level of leakage current
Type CF-rated supplies must conform to a leakage current limit of 10μA under normal conditions
The level of leakage current from the power supply to the patient must be extremely low and must comply with the requirements specified by the standard to qualify as medical grade power supply.
For instance, as per the standard, type CF-rated supplies must conform to a leakage current limit of 10μA under normal conditions (NC) and 50μA for single fault conditions (SFC). Likewise, the BF- and B-rated supplies must keep the leakage current limit at 100μA under NC and 500μA for SFC (Table 2).
To meet these strict leakage limits, it is common to use separate DC/DC converters for each output for enhanced isolation and to avoid crosstalk between outputs.
How IEC 60601-1 Addresses EMC Concerns
With the exponential growth of devices like smartphones, laptops, and tablets that use cellular networks, Bluetooth, Wi-Fi, and other wireless protocols to communicate, there is a possibility of medical equipment malfunctions caused by electromagnetic or radio frequency interference.
Additionally, it is commonplace for several pieces of medical equipment to be clustered around a single patient and they must not interfere with each other.
the fourth edition of the IEC
Consequently, medical equipment must be immune to high-frequency fields up to 2.7GHz
The fourth edition of the IEC standard addresses EMC concerns the much more stringent requirements with regards to electromagnetic immunity and susceptibility for medical equipment compared to commercial or industrial standards.
Consequently, medical equipment must be immune to high-frequency fields up to 2.7GHz (200MHz higher than industrial limits) and steps must be taken to prevent damage caused by electrostatic discharge (ESD) – for example, for contact discharge, the threshold went up from 6 to 8kV, and for air discharge, it has been increased from 8 to 15kV.
Summary
Looking at the challenges and complexity of complying with the rigorous medical standards, it makes sense for medical equipment builders not to build their power supplies, but to install pre-certified medical grade power supplies from a reliable manufacturer who can guarantee compliance with the latest standards as well as offering high efficiency and reliability.
Over the years, RECOM has earned that reputation in the medical realm. It is a manufacturer that can offer a broad portfolio of high-performance medical-grade converters that can meet and beat your requirements. Designers at RECOM are constantly tracking the changes in the IEC 60601-1 medical standard and ensuring that our medical power supplies meet or exceed the latest specifications.
REM and RACM series
RECOM's modular REM and RACM series converters offer complete, compliant solutions that reduce design time, simplify end-user certification, and provide faster time to market.
These medical-grade DC/DC converters and the AC/DC power supply series are designed to comply with the international medical safety standard, ES/IEC/EN 60601-1 3rd Edition, ensuring safety for patients and practitioners alike. All components include the characteristics necessary for medical environments including reinforced isolation with two means of patient protection (2MOPP), > 8mm creepage and clearance distances, and low leakage (BF and CF ratings).
