Chapter 3 Electrical Safety

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Chapter 3Electrical Safety
2
Electrical Hazards
Florence Nightingale "The hospital should do
the sick no harm" Electrical Shock ???, ??,
???, ?? ? ?? ?? ?? ????? ???
??? ??? ??? ??? ??? ? ?? Macroshock ????
??? ??? ?? ??? ??? ??? ?????? ?? ??? ?? ?? ???
??, ??, ????, ???? ?? ?? tetanizing stimulation
of heart, lungs, brain, Microshock ??? ??? ??
??? ?? ??? ??? ?? ?? catheter, pacemaker wire
(10uA? ???? heart fibrillation ?? ??)
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Electrical Hazards
4
Receptacles Connected to the Fuse Panel
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Macroshock (two-wire unit)
Hot wire? ?? lead? short
Hot? neutral? reverse Chassis? ??? short
Hot wire? chassis? short
Neutral wire? case? short
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Macroshock (three-wire unit)
Hot wire? ?? lead? short
2 wire system? ??
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Macroshock Hazards
A. Leakage current ???????? ?? case? ???? ???
?? (?????? leakage
current? ground wire? ??? ????) Inductive
coupling to the chassis or to the patient's lead
on equipment - power supply transformer ??
??? motor? ?? ??? chassis? lead ??? ??
Capacitive coupling - ??? ??? ??? ?????
?? - ??? ??? ?? ? ???? dielectric? ??
????? ? ?? - Leakage current? ???
power-side capacitance? ?? Resistive
coupling ??(??)? ????? ?? B. Chassis Voltage
Neutral wire? chassis? ????? ?
120 V, 500W instrument has 0.25
power code resistance
Neutral? ground ??? ????
Neutral wire? ?? ??? ??
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Path of Leakage Current with Defective Ground Wire
Leakage current
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Normal Path for Leakage Current
Leakage current
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Microshock Situation with Two-wire Unit
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Microshock Situation with Three-wire Unit
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Ground Fault Interrupter
IH
IN
IF
Normal IH IN Hot wire fault or touches hot
wire IF flows through ground If it exceeds the
limits Relay works
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Power Line Isolation Transformer with Fault
Detector
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Single Isolation Failure
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Electrical Hazard (case 1)
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Electrical Hazard (case 2)
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Electrical Hazard (case 3)
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Design Considerations for Reducing Electrical
Hazard