1. FYS 4250
Kap.14
Electrical safety

2. Electric current, perception- and hazard thresholds
device related patient injuries in USA each year
Three phenomenon with current through the body:
Electric stimulation of excitable tissue (nerve & muscle)
Resistive heating of tissue
Electrochemical burns and tissue damage for direct current and very high voltages
Perception = tingling sensation

3. Electrovibration (1uA 50Hz)

4. Statistical scattering of sensitivity for electric current

5. Frequency dependency and spread of the let-go threshold
Let go current rais below 10 Hz, muscles can partially relax during part of each cycle

6. Ventricular fibrillation thresholds in animals
Duration of applied current is an important factor.

7. Macro- og microshock
Macroshock 100 mA
Microshock 10 uA

8. Electromedical devices must be CE-marked (Europe)

9. Patient near PC (B-apparatus)

10. American electric power distribution

11. 4-leads (norske), og 5-leads (europeiske) electrical circuits fra ”Medisinsk-teknisk sikkerhet på sykehus” Grimnes&Jensen 2003
Norwegian elctrical network is floating with respect to ground = IT network (No current dropout for the first ground short circuit
European TN.

12. Isolated system

13. Macroshock due to ground fault

14. Microshock, two error situations

15. Ventricular fibrillation and pump failure vs catheter area

16. Micro-shock
A device with a ground fault that does not open the circuit breaker.
5 A flow to the distribution panel on the ground wire. Ground wire have 0.1 ohm resistance -> 500 mV could appear across the patient.
Resistance of a patient’s body and liquid filled catheter is less than 50 kOhm -> current = 10 uA

17. System for grounding

18. Ground fault circuit-interupter
Disconnect the source of electric power when a ground fault greater than 6 mA occurs.
Senses the difference between the hot conductor and neutral conductor
Trip time varies inversely with the magnitude of the ground-fault current

19. Floating
Patient

20. Electrical isolation
Perfect isolation barrier modeled by the isolation capacitance and resistance.
IMRR = isolation mode rejection ratio (potential between the input common and the output common)

21. Electric isolation

22. Isolated pressure transducer

23. Receptacles tests

24. Ground pin to chassis test
Should not exceed 0.2 Ohm

25. Chassis leakage cuttent test

26. Patient leakage current test

27. Leakage current between patient leads

28. Isolation test for AC isolation
Equipment manufacturer only, may be omitted for testing in health care facilities