Main questions

Ground Fault Circuit Interrupter (GFCI)

(DISEGNO CIRCUITO) It prevents fires from short circuits and other electrical faults that don't involve humans. A ground fault is an unintentional electrical path between a power source and a grounded surface. It occurs usually when equipment is damaged or defective, such that live electrical parts are not protected from contact. If your body provides a path to the ground for this current, you could be burned, shocked, or electrocuted.

A GFCI constantly monitors current flowing through a circuit. If the current flowing into the circuit differs by a very small amount, such as 5mA, from the returning current, the GFCI interrupts power very fast to prevent a lethal dose of electricity. It uses an internal solenoid that mechanically trips the built-in circuit breaker.

The GFCI uses a differential transformer to compare the outgoing current on the hot wire with the incoming current on the neutral. If a GFCI device trips and the fault is later fixed, then the user can reset the GFCI by pushing the reset button.

There is also a test button which will cause the GFCI to trip if it is working properly. Should be tested once a month! Typical value of leakage current = 5mA. GFCI are available in 2 types:

1. The circuit breaker, installed in an electrical panel;
2. The receptacle type, installed into an electrical box;

3) INSULATED POWER SUPPLY

Electrical Hazard Protections

• Insulation: Plastic or rubber coverings that do not conduct electricity. Insulation prevents live wires from coming in contact with people thus protecting them from electrical shock.
• Grounding: Grounding is another method of protecting you from electric shock. However, it is normally a secondary protective measure. The "ground" refers to a conductive body, usually the earth, and means a conductive connection, whether intentional or accidental, by which an electric circuit or equipment is connected to earth or the ground plane. By "grounding" a tool or electrical system, a low-resistance path to the earth is

intentionally created.

• Guarding;
• Electrical protective devices;
• Personal Protective Equipment Safe work practices

Isolated power systems are designed to protect patients and personnel from electric shock in care areas, maintains the continuity of power in the case of a first line-to-ground fault, and continuously monitor the cumulative hazard current from all connected equipment.

If there is a fault, the system alarm in the isolation panel activates, and the critical medical equipment remains operational because no ground fault protection or overcurrent protective device trips.

The triggering of an alarm from a single ground fault must be rectified as soon as possible at a safe time, as a second ground fault could trigger the short circuit protection and take an entire operating room offline.

The IPS is a system comprising an isolated transformer, a line isolation monitor (LIM) and its ungrounded circuit conductors.

The LIM is a test instrument designed to continually check the balance

and unbalance impedance from each line of an isolated circuit to ground and equipped with a built-in test circuit to exercise the alarm without adding to the leakage current hazard. - No macroshock hazards for a single fault condition - No sparks with single fault condition - Single fault does not affect performance - If there is a single fault condition, problems may last for a long time before being detected - System becomes uninsulated and if there is another fault heavy current will flow 4) ELECTRICAL MEASUREMENT ON BIOMEDICAL DEVICES Applied Part or Patient Leakage is the most important part of the leakage measurement on any medical device. Applied Parts are directly in contact with the patient and are in case of invasive devices placed under the patient's skin, which forms our natural protection against electrical currents. Currents applied under the skin can result in far greater consequences. Currents as low as 15 μA can result in fatality. The limits for

leakage currents within the IEC 60601-1 requirements are set to minimizing the probability of ventricular fibrillation to a factor as low as 0.002 (Limit of 10 μA for CF Applied Part under normal condition).

It is important to verify that a Medical Device with moving parts (e.g. motor or pump) is safely mounted to allow movement without causing damage to equipment or personnel. Secondary Earth paths will effect the leakage measurements and might give false PASS readings. Always make sure that the device under test is positioned safely and isolated from Earth when measuring leakage.

To ensure a traceable simulation of current as if passing through a human body, measurement circuits have been designed to simulate the average typical electrical characteristics of the human body. These measurement circuits are referred to as Body Models or Measuring Device (MD in IEC 60601-1).

IEC 60601-1 specifies that all leakage measurements should be carried out using normal and single fault conditions.

Typical part of the electrical safety testing procedures is to perform the test as follows:

1. Normal Supply Voltage No (SFC)
2. Normal Supply Voltage Open Neutral
3. Normal Supply Voltage Open Earth
4. Reversed Supply Voltage No (SFC)
5. Reversed Supply Voltage Open Neutral
6. Reversed Supply Voltage Open Earth

The Earth Leakage Test shows the current flowing through or via the insulation of the Medical Device into the protective Earth conductor.

• Earth Leakage, normal conditions - This test measures the Earth Leakage current under normal conditions. The current is measured through the Measuring Device with S1 closed and S5 normal and then S5 reversed.
• Earth Leakage, single fault, supply open - This test measures the Earth Leakage current with a single fault condition (supply open). The current is measured through the Measuring Device with S1 open and S5 normal and then S5 reversed.

Enclosure Leakage displays the current that would flow if a person came into contact with the

housing (or any accessible part not intended for treatment or care) of the Medical Device.

• Enclosure Leakage, normal condition - This test measures the enclosure leakage current under normal conditions. The current is measured through the Measuring Device with S1 and S8 closed and S5 normal and reversed.
• Enclosure Leakage, single fault, supply open - This test measures the enclosure leakage current with a single fault condition (Earth open). The current is measured through the Measuring Device with S1 open, S8 closed and S5 in normal and then S5 reversed.
• Enclosure Leakage, single fault, Earth open - This test measures the enclosure leakage current with a single fault condition (Earth open). The current is measured through the Measuring Device with S1 closed, S8 open and S5 in normal and then S5 reversed.

The Patient Leakage Current is the current flowing from the Applied Part via the patient to Earth or flowing from the patient via an Applied Part to Earth, which originates

from an unintended voltage appearing on an external source.

• Patient Leakage, normal condition - This test measures the Patient Leakage Current under normal conditions. The current is measured through the Measuring Device with S1 and S8 closed, S5 normal and then S5 reversed.
• Patient Leakage, single fault, supply open - This test measures the Patient Leakage Current with a single fault condition (supply open). The current is measured through the Measuring Device with S1 open, S8 closed and S5 normal and then S5 reversed.
• Patient Leakage, single fault, Earth open - This test measures the Patient Leakage Current with a single fault condition (Earth open). The current is measured through the Measuring Device with S1 closed, S8 open and S5 normal and then S5 reversed.

The Patient Leakage F-Type Test (also known as mains on Applied Parts test) displays the current that would flow if a mains potential was applied to the Applied Part which was attached to a patient (i.e. a single fault condition).

closed, S5 normal and then S5 reversed.• Patient Auxiliary, single fault, supply shorted - This test measures the patient auxiliary current under a single fault condition (supply shorted). The current is measured through the Measuring Device with S1 closed, S8 closed, S5 normal and then S5 reversed.• Patient Auxiliary, double fault - This test measures the patient auxiliary current under a double fault condition. The current is measured through the Measuring Device with S1 open, S8 open, S5 normal and then S5 reversed.

closed and S5 normal and then S5 reversed.• Patient Auxiliary, single fault, Earth open - This test measures the patient auxiliary current under a single fault condition (Earth open). The current is measured through the Measuring Device with S1 closed, S8 open and S5 normal and then S5 reversed.

5) EFFECT OF AN ELECTRIC SCHOCK ON HUMAN BODY

Research shows that minimal let go current occurs for commercial power line frequencies: 50 and 60Hz. The let go current (or release current) is the maximum value of electric current through the body of a person at which that person can release himself or herself.

Skin resistance Z ranges from 10 kΩ to 1 MΩ (per cm squared^2). If skin is wet or broken, Z may drop to 1% of its original value.

When a person becomes part of the circuit touching a wire, the current enters the body from the wire and leaves it from the earth. Physiologically, the effect of electricity on the human body are muscle cramps, respiratory arrest, ventricular fibrillation,

Burns (heating) and electrolysis.

The four major types of electrical injuries are:

• Electrocution
• Electrical Shock - Received when current passes through the body. Severity of the shock depends on:
  1. Path of current through the body.
  2. Amount of current flowing through the body.
  3. Length of time the body is in the circuit.
• The longer the exposure, the increased danger of shock to the victim. Low voltage can be extremely dangerous because the degree of injury depends not only on the current, but on the length of time in contact with the circuit. (Example: A current of 100mA applied for 3 seconds is as dangerous as 900mA applied for 0.03 seconds). Low Voltage Does Not Mean Low Hazard.

High voltages lead to additional injuries such as:

• Violent muscular contractions. Muscle contractions may cause bone fractures from either contractions themselves or from falls.
• Internal bleeding, destruction of tissues.