|Year : 2015 | Volume
| Issue : 12 | Page : 769-773
Does non-medical grade power cord compromise the safety of medical equipment?
V Padmavathi1, PS Vishnu Prasad2, Pankaj Kundra3
1 Division of Biomedical Engineering, JIPMER, Puducherry, India
2 Department of Biomedical Engineering, MGMCRI, Puducherry, India
3 Department of Anaesthesiology and Critical Care, JIPMER, Puducherry, India
|Date of Web Publication||11-Dec-2015|
Division of Biomedical Engineering, JIPMER, Puducherry
Source of Support: None, Conflict of Interest: None
A tertiary care 1000 bedded hospital contains more than 10,000 pieces of equipment worth approximately 41 million USD, while the power cords supplied along with the imported equipment do not comply with country-specific norms. Moreover, the local vendors procure power cords with type D/M plug to complete installation and also on-site electrical safety test is not performed. Hence, this project was undertaken to evaluate the electrical safety of all life-saving equipment purchased in the year 2013, referring to the guidelines of International Electrotechnical Commission 62353, the Association for the Advancement of Medical Instrumentation (AAMI) and National Fire Protection Association (NFPA)-99 hospital standard for the analysis of protective earth resistance and chassis leakage current. This study was done with a measuring device namely electrical safety analyser 612 model from Fluke Biomedical.
Keywords: Device under test, electrical safety test, equipment leakage current, protective earth resistance
|How to cite this article:|
Padmavathi V, Vishnu Prasad P S, Kundra P. Does non-medical grade power cord compromise the safety of medical equipment?. Indian J Anaesth 2015;59:769-73
|How to cite this URL:|
Padmavathi V, Vishnu Prasad P S, Kundra P. Does non-medical grade power cord compromise the safety of medical equipment?. Indian J Anaesth [serial online] 2015 [cited 2021 Jun 21];59:769-73. Available from: https://www.ijaweb.org/text.asp?2015/59/12/769/171556
| Introduction|| |
The power source for all equipment is alternating current (AC) with frequency - 50Hz; unfortunately, humans are most sensitive to this frequency.  Some of the effects are tissue injury, burns, and fibrillation of the heart.  The main cause for these effects are leakage current which occurs naturally in all the electrically operated equipment due to stray capacitance between two wires or wire and metal chassis. This can be eliminated by generating a low resistance path from equipment to ground, ideally at zero potential.
Though the equipment is designed with the highest degree of protection, safety is attained only when there is a proper connection between the equipment and hospital earth by a component called power cord. If the protective earth resistance (PER) is not as per the International Electrotechnical Commission (IEC) norms, the safety of equipment is violated. Therefore, during installation of medical equipment, electrical safety test is highly required to conform various safety parameters described by IEC 62353.  The initial tested data serves as a reference guide for recurrent test throughout the working lifetime of each equipment. In future, on the recurrent test, the deviations of ground integrity and leakage current can be monitored for necessary corrective actions. It is now clear that all the life-saving equipment must undergo electrical safety test on recurrent intervals to ensure safe operation.
The purpose of this project was to find out the root cause and influence of environmental factors for equipment failures during the first year of purchase. In addition, implementing electrical safety checks on recurrent intervals to guarantee safe usage of equipment on the patient are discussed.
| Methods|| |
We conducted electrical safety study on 200 life-saving equipment purchased in the year 2012-2013 in Jawaharlal Institute of Postgraduate Medical Education and Research, Pondicherry [Table 1]. They belonged to Class I category with detachable power cords of power consumption <1.5 KVA (kilovolt ampere). Class II category, non-detachable power cord equipment and permanently installed equipment were excluded from the testing. Since all the tested equipment were newly purchased, the influence of film resistance was excluded.  The electrical safety analyser (ESA) 612 model was used which is capable of measuring low resistance up to 2 Ω with an accuracy of ±2% and leakage current from 0 μA to 1999 μA with an accuracy of ±1%. The analyser incorporates test algorithm of Association for the Advancement of Medical Instrumentation(AAMI)/National Fire Protection Association (NFPA)-99 hospital standard and IEC 62353.  All the measurements were manually obtained for better accuracy.
The standard test protocol involves two components; visual inspection and electrical testing.
The equipment in working condition can only be tested for electrical safety. This method identifies the equipment type, model, power consumption, power cord type D/M and fuse ratings. In addition, it also checks site condition inclusive of input power and electrical socket where equipment is being used.
Electrical safety test
The electrical safety test involves PER and leakage current measurements. The device under test (DUT) will be powered through the measuring device (MD) and testing probe performs the measurement. While testing, all other external communication/data lines such as video graphics array and Ethernet cables must be removed from the DUT to eliminate parallel earth. 
Protective earth resistance/earth bond testing
'Earth bond testing' tests the integrity of the low resistance connection between the earth conductor and any metal conductive parts, which may become live in case of a fault on Class I medical devices. Although many Class I medical devices are supplied with an earth reference point, most if not all medical devices require multiple earth bond tests to validate the connections of additional accessible metal parts of the enclosure. The test current is applied between the earth pin of the mains supply plug and any accessible metal part (including earth reference point) via a dedicated earth bond test lead (clip/probe). The test method of Class I equipment in reference to the 62353, IEC 2007 (IEC 683/07) guideline is shown in [Figure 1].
|Figure 1: Test method for protective earth resistance for Class I equipment|
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The MD ESA 612 applies a test current of 200 mA to determine PER and the highest reading will determine pass or fail criteria.  The allowable test limits are based on IEC 62353 and AAMI guideline: 100 mΩ - for a detachable power cable up to 3 m; 300 mΩ - for a Class I device including power cable (not exceeding 3 m) and 500 mΩ - for a medical system as per AAMI/NFPA-99 hospital standard. An increase in resistance may indicate loosening/corroded connection or damaged or non-standard cables, which need to be repaired before continuing with the leakage test.
Class II equipment and double-insulated devices do not have a protective earth. It is, therefore, neither necessary nor possible to measure earth continuity; this poses no safety risk. 
Research has shown that current, not voltage, is often the source of injury or death. , It takes a small amount of current to cause major consequences. For this reason, the International Electrotechnical Committee has set stringent rule on the design of medical equipment, so as to prevent any patient or operator being exposed to currents not part of the functional operation of the device. These currents are referred to as leakage currents. The guideline for an in-service test of medical electrical equipment IEC 62353 defines
two different types of leakage current: equipment leakage current and applied part/patient leakage current.  To measure these currents, the guideline describes three methods: direct method - the current flowing down the protective earth conductor of the mains inlet to lead; differential method - the result of imbalance in current between the live conductor and neutral conductor and alternative method - current flowing through a person to earth from the applied part or current flowing from a person to earth via the applied part by applying unintended voltage from an external source.
The direct method is identical to the method used in the IEC 60601-1 standard, measuring the true leakage through a body model (MD) to earth (the measurement of leakage current through body model circuit). This method can measure both AC and direct current leakage with the highest accuracy compared to all other methods. Therefore, in the analysis, we have selected this method for measuring equipment leakage current.
Equipment leakage current
The total leakage current is derived from the applied enclosure and mains part. All applied (types B, BF and CF) and non-earthed accessible conductive parts are grounded together and connected to earth via 1 KΩ MD (body model). The test is conducted with the protective earth connection interrupted, to ensure the measurements are done under worst conditions. Measurements were carried out in both the polarities and single fault condition. The allowable value for leakage currents in single fault condition was 500 μA, and PER limit is 300 mΩ referring to 62353 IEC: 2007 (IEC 704/07).
| Results|| |
Electrical safety test was performed on 200 critical care equipment purchased in 2013 of 8 different categories (anaesthesia delivery systems, defibrillators, Intensive Care Unit ventilators, humidifiers, electrosurgical unit syringe pumps, cardiac output monitors and multiparameter monitors). Out of 200 equipment, 122 (61%) passed the testing of PER and leakage current as per the guideline IEC 62353 and AAMI/NFPA-99 hospital standard test. Further, 62 (31%) equipment failed as per IEC 62353 and 49 (24.5%) equipment failed as per AAMI/NFPA-99 hospital standard. Nevertheless, in both, 28 (14%) of equipment failed with safety standards. The test result comparison values for 200 equipment with IEC and AAMI/NFPA-99 safe limit are shown in [Figure 2].
|Figure 2: Protective earth resistance and leakage current values in single fault condition for all the tested 200 equipment (IEC 62353 and AAMl)|
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Out of failed equipment, 20 numbers were again retested with medical grade power cord (meeting IEC 60601 standards) and non-medical grade power cords (supplied by the vendor). The comparative results of PER and leakage current are presented in [Table 2]. We applied Mann-Whitney U-test, assuming the hypothesis 'there is no difference between medical grade power cord and non-medical grade power cord with a significance level of 0.99. The exact output significance of this test was 0.000, hence the hypothesis was rejected. The results of PER comparison are represented in [Figure 3]. These values were also represented in boxplot shown in [Figure 4].
|Figure 3: Describes the protective earth resistance values of selected 20 equipment, which was tested with medical and non-medical grade power cords|
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|Figure 4: Illustrates the distribution of equipment between medical grade power cord and non-medical grade power cord. The boxplot illustrates the difference between protective earth resistance and leakage current values obtained between medical grade power cord and non-medical grade power cords for selected 20 equipment only. Data shown as median (horizontal line), interquartile range (box), 25th to 75th percentile (vertical line). *P=0.000 Non medical grade versus medical grade power cord|
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|Table 2: Electrical safety test results of selected 20 equipment tested with medical grade power cord and non-medical grade power cord|
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| Discussion|| |
The conduct of electrical safety test has identified a range of causes that circumvent safety aspects in life-saving equipment. The test results confirmed that 28 equipment failed the tests and unsafe to use on the patient as well. These failed equipment on further investigation showed 80% failure due to deviant power cord usage.
Guideline IEC 60601-1 defines that a medical grade power cord must have plug type D and a mains supply cable of 3 m length with a minimum cross-sectional area of 0.75 mm and resistance of the cord <100 mΩ. If the wire thickness or purity of copper or materials used in the cable do not meet the IEC medical equipment guidelines, the ground resistance value may deviate and results in higher PER. Hence, to find out significant differences between medical grade and non-medical grade power cords, a comparative study was performed. The hypothesis for this study assumed no significant differences between the power cords. However, the acquired Mann-Whitney exact output significance was 0.000. The median of PER value of medical grade power cord was 84.5 mΩ followed by a median of non-medical grade power cord 580 mΩ. From this analysis, it is clear that there is a significant difference in the usage of power cord types B and A.
The study also confirmed that use of medical grade power cord has maximized the flow of leakage current to ground. Therefore, if PER increases, the fault/leakage current will find unintended paths that could include patient or operator. The other reasons of 18% failure were due to the instrumentation errors, harmonic distortion issues and possible intermittent dilemmas.
It is well-known that medical equipment is one of the largest capital investments of every healthcare organisation, often involved in patient incidents that resulted in serious injuries or deaths.  At present, our system guarantees preventive maintenance for equipment, but safety is not ensured. International Standard Guideline IEC 62353-2007 'medical electrical equipment-recurrent test and test after repair of medical electrical equipment', document applies to testing of medical equipment and medical electrical systems, which comply with IEC 60601-1 before putting into service, during maintenance, inspection, servicing and after repair or on occasion of recurrent test to assess the safety of such medical equipment. Therefore, this study proposes to implement an electrical safety test protocol in healthcare organisations to get benefits in 3 ways from electrical hazards. First, protect patient, user and equipment from possible abuse to which the device may be exposed. Second, it will save equipment from harmful influence of harmonics caused by neighbouring equipment. Third, equipment's leakage current can be conformed to the safe limit during any catastrophic failure.
Moreover, the conduct of electrical safety test will also eliminate the subsequent incidents reported in our operation theatre which was one of the reasons that encouraged us to conduct this study. We experienced a fire incident, where power cord's plug top burnt off completely. On root cause analysis, we found that the plug type was non-Ingress Protection (IP) rated; the saline solution had entered into the socket and created a short circuit path. This was because the supplier had cut-off the plug type F from the cord and replaced with plug type D (Indian standard). Both root cause analysis and our study concur with the result. Hence, we recommend using medical grade IP 44 or above rated power cord with type D plugs; if not, it compromises the safety of medical equipment.
| Conclusion|| |
On consideration of patient safety, this review provides evidence that safety is attained only when there is a proper connection between equipment and hospital earth by a major component called power cord. Hence, we recommend performing on-site electrical safety test using a suitable electrical safety analyser during installation and annual maintenance to validate and confirm that medical equipment along with power cord are safe and reliable to use in patient care.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2]