Electrical distribution systems need regular examination:
Few types of equipment are as regulated as the medical electrical equipment that falls under the auspices of the requirements in the International Electrotechnical Commission IEC 60601-1 Ed. 3.0 b:2005 Standard for Medical Electrical Equipment, Part 1: General Requirements for Safety. The Technical Committee (TC) 62 of the IEC publishes the standard, which is harmonized with the Underwriters Laboratories (UL) 60601-1 and is adopted by most of the world’s regulatory agencies.
The Food and Drug Administration (FDA) recognizes IEC 60601-1 as a consensus standard with the following concerns, according to www.fda.gov: “This standard should serve as a baseline for all of the appropriate device areas. However, where there are existing Center for Devices and Radiological Health [CDRH] guidance documents with additional electromagnetic compatibility [EMC] specifications, then these will supersede the basic IEC requirements.” However, the possible effects and sources of power quality phenomena related to medical electrical equipment seem to elude both the consideration of the IEC and FDA.
Hospitals and medical imaging equipment suppliers have long been purchasers of power quality monitors. The Electrical Power Research Institute (EPRI) has had a healthcare initiative for a number of years to assist the industry through education and the use of electrotechnology solutions that will reduce risk and liability, meet regulatory compliance demands and provide work toward improving the quality of patient care. But the regulating documents have such specifications, as clause 49.2 states, “where the interruption and restoration of power supply does not result in a safety hazard other than the interruption of the intended function.”
Overall, the standard covers the safety of the patient connected to the equipment. Clause 36 covers electromagnetic compatibility, which refers to IEC 60601-1-2 for differing or additional EMC requirements for specific types of medical equipment, but not necessarily all of those disturbances that typically fall under the realm of power quality phenomena and that the electrical supply may contain.
Preventing electrical shock hazards requires the equipment to be subjected to the appropriate dielectric and be able to withstand test voltages as well as measure the leakage current, earth bond and insulation impedance, residual voltage and the touch potential in the event of component failure. Several instrument manufacturers, such as Gossen Metrowatt, Quadtech and BAPCO, have instruments designed to verify compliance with such electrical safety aspects.
But what about the effects of waveform distortion of the supply voltage, high-frequency transients, voltage variations or combinations of them during a typical power quality disturbance? Will the image produced by MRI, ultrasonic and CAT scan equipment be accurate representations to the medical staff in the presence of such, or will it just be an expensive and discomforting “interruption of the intended function”? Whereas 60601-1-2 provides the test levels and defines pass/fail criteria while referring to CISPR 11 for emission and the IEC 61000-4-x standard for measuring immunity, it seems to fall short of ensuring proper operation, in a similar manner where a piece of equipment can obtain the CE mark bypassing the IEC 61010-1 tests yet become a victim of power quality phenomena.
Protection against power quality disturbances goes beyond the proper design and manufacturing of medical electrical equipment. The electrical infrastructure of the medical facility should go beyond meeting the requirements of the National Electrical Code (NEC) or the local requirements. Just as the equipment is tested when manufactured and retested periodically out in the field for leakage current, insulation resistance and proper ground bonding, the electrical distribution system within the facility should be similarly tested upon completion of the construction phase as well as periodically once the facility is in operation. Like most facilities, medical operations are electrically dynamic, changing as new loads are introduced and building expansion takes place to meet the demands for improved healthcare. Increased use of information technology equipment, such as computers, printers and networks, also adds potential sources and victims of power quality phenomena.
A proactive electrical measurement program to ensure the integrity of the grounding system, the quality of the electrical supply and the proper operation of the backup generation is as essential to the patient’s safety as the testing of the medical equipment itself. While it is rarely possible to shut down part of the facility for periodic testing, it is possible to do online testing using power quality monitors and ground impedance testers that can help diagnose the electrical health of the facility. As the adage goes, “An ounce of prevention is worth a pound of cure.” •
BINGHAM, a contributing editor for power quality, can be reached at 732.287.3680.