Topic 4.3 Flashcards
What is leakage current?
Leakage current is the result of small amount of current that flows from the wiring to the metal chassis. This is not the result of fault but by the natural outcome of using wiring and components
What are the 2 types of leakage currents?
1) Capacitive Leakage
2) Resistive Leakage
What is Capacitive Leakage Current?
It is the result of capacitance that is from between the wire and the metal chassis, where the metal wire and the metal chassis are like the two capacitive plates, while the wire insulation act as a dielectric material
What is Resistive Leakage Current?
Resistive Leakage current is the result of the resistance of the insulation of power wires absorbing some current and coming into contact with the chassis and also transformer primary winding
What is the 2 purpose for Earth wire?
1) Drain off leakage current
2) Blow off the plug fuse in case of live to metal chassis short (prevent electric shock to anyone who touch the chassis)
How do we prevent Macroshock and Microshock?
We basically need to ground our casing/chassis of our medical devices as humans have a high resistance thus the current will flow away if we have a grounded casing/chassis
What are the 2 ways to provide electrical safety in hospital?
1) Control the availability of electric power
2) provide proper grounding in patients’ environment
What is the 3 Stages of Electrical Distribution?
1) Transmission ( Voltage come from power plant )
2) Substation ( step down high voltage )
3) Domestic power supply ( your wall plug )
Describe the grounding system in ICU ward setting
All the Plug/Receptacle grounds and conductive surfaces in the ward is connected to a patient-equipment grounding point from the PEGP it is than connected to the reference grounding point and down to the building ground
What are the 3 most common circuit techniques to prevent electric shock?
1) Isolation Transformer
2) Ground fault Circuit interrupter
3) Line Isolation Monitor
How does Isolation transformer work?
It works by grounding the primary winding and not the secondary winding, hence when person is in contact with secondary live or neutral, there is no ground to complete the connection for electric shock
What is a Line Isolation Monitor?
It is to continually analyze the entire isolated circuit to monitor the leakage current to current and provide audible alarms and signal when the current exceeds certain magnitude but does not trip the circuit
How do we identify the faulty equipment when the Line isolation Monitor alarm goes off?
Unplug equipment one by one to see which equipment stop the alarm from ringing
What is a Ground fault Circuit interrupter?
It is basically the same as an RCCB and it detects the leakage current from the live and neutral wire in the mA. if the current is imbalance the circuit will trip and cut off power by opening the live wire.
