Leakage current

Describes about the effect of leakage current in patient safety

1. LEAKAGE CURRENT By, Pavithra S

2. Definition Is an inherent flow of non-functional current from the live electrical parts of an instrument to the accessible metal parts. Leakage currents usually flow through the third wire connection to the ground . They occur by the presence of a finite amount of insulation impedance, which consists of two parts: capacitance and resistance Leakage currents due to capacitance develop because of the presence of capacities between any two conductors separated in space Instruments are generally designed so that leakage current flows to the instrument case and then to the ground via the three-wire power cord provided with the instrument. 4/8/2021 2

3. Types 4/8/2021 3 Enclosure Earth Patient Divided according to the current path

4. Enclosure Leakage Current 4/8/2021 4 The enclosure leakage current is the current which flows, in normal condition, from the enclosure or part of the enclosure through a person (or an external conductive part other than the earth connection) in contact with an accessible part of the enclosure to earth or another part of the enclosure. This current becomes significant when the person touching the equipment is connected to earth either directly or via a large capacitance

5. Earth Leakage Current 4/8/2021 5 The earth leakage current is the current which flows, in normal condition, to earth from the mains parts of an apparatus via the earth conductor

6. Patient Leakage Current 4/8/2021 6 The patient leakage current is the current which flows through the patient from or to the applied part of the patient circuits. This current does not include any functional patient current.

7. Importance of Grounding 4/8/2021 7 In almost all equipment's leakage currents do flow to the ground from the ac supply operating the device. This current may not prove hazardous if there is a good grounding system to drain it away. In most of the cases, the instrument ground and the ground to which the patient is connected is the power ground. Dangerous potentials have been measured in the operating rooms between power grounds at different outlets or between power grounds and the water pipe or earth ground. Voltages as high as a few hundred millivolts have been measured between the power ground (third pin of the socket) and the water pipe nearby. These are the voltages which, if applied to a catheter positioned in the heart of a patient, could prove fatal.

8. LEAKAGE CURRENT MEASUREMENT 4/8/2021 8 Leakage current measurement is performed as part of the  safety test  of an electrical device. The currents flowing through the protective conductor or metallic parts of the earth are measured. Alternating currents can occur such as the through capacity of lines, coils etc. It can even flow with a proper insulated earth. If these flows are too high, it becomes a hazard.

9. Procedure of leakage current measurement 4/8/2021 9 Leakage current measurement is conducted under operating and fault conditions. By definition, the operating voltage is 110%. The current is measured by a measuring device that simulates the resistance of the human body (2kΩ). The measurement is carried out in three modes of operation of a single phase device under test, with the exception of medical devices, according to the following methods:

10. Method 1 4/8/2021 10 leakage current measurement between neutral conductor and PE

11. Method 2 4/8/2021 11 leakage current measurement between phase and PE

12. Method 3 4/8/2021 12 leakage current measurement between phase and neutral conductor and PE

13. 4/8/2021 13 If a three-phase system is being tested, the leakage current is measured from the star point against PE. Here , an interruption of the individual phases is provided. The limits are defined according to the standards.

14. Electrical System without Earthing 4/8/2021 14

15. Earthing 4/8/2021 15

16. Approaches to protect against shock 4/8/2021 16 The Patient is completely isolated and insulated from all ground objects and all sources of electric current All the conductive surfaces within the reach of the patient is maintained at same potential Extra protection needs to be given to patients who Has reduced skin resistance Has invasive conditions Has exposure to wet conditions like dialysis.

17. Thank You 4/8/2021 17