Primary FRCA Course Electrical Safety Exam Prep Questions Flashcards
In micro shock:
The current is too small to be harmful
False. Even small currents applied directly to the heart produce a current density sufficient to have a biological effect
In micro shock:
The frequency of the current is not important
False. The effect of frequency in microshock is the same as in macroshock. Higher frequency means that charge is moved less far as oscillations are more frequent. So in the case of the body, the ions are moved less far, therefore less likely to cross the cardiac membrane and cause VF.
In micro shock:
The right ventricle is more sensitive than the left
True.
In micro shock:
The current must be greater than 100uA
False. Currents of over 50uA are sufficient to have an effect
In micro shock:
The current may induce asystole
False. Typically cause VF especially if delivered during repolarisation.
In electric shock:
Frequencies of >10KHz do not cause arrhythmias
False. It depends to some extent on the size of the current, but the frequency should be >100KHz
In electric shock:
Effect depends upon the duration of current flow
True. Both energy delivery and ion shifts depend upon ‘quantity’ of charge passed (current and time)
In electric shock:
Current mainly affects the flexor muscles
False. But your forearm flexors are stronger than your extensors, hence the inability to ‘let go’
In electric shock:
Effect depends on the total amount of energy delivered
True. Both energy delivery and ion shifts depend upon ‘quantity’ of charge passed (current and time)
In electric shock:
Electrons flow through the body
False. The charge carriers in the body are ions
The electricity supply to an operating theatre:
Is a three phase supply
False. Only a single phase is supplied to the operating room. Three phase is supplied to hospital substation.
The electricity supply to an operating theatre:
Consists of Live, Neutral and Earth wires
False. LINE neutral and earth wires
The electricity supply to an operating theatre:
Has a voltage of approximately 240 volts
True.
The electricity supply to an operating theatre:
Has an Earth connection from the substation
False. The substation earth (star point) creates the ‘Neutral’ wire. The earth connection is a local earth
The electricity supply to an operating theatre:
Varies sinusoidally at 50 Hz
True. Mains frequency is held very close to 50 Hz in europe (60 Hz in the USA)
Electrostatic interference from a piece of equipment:
Requires a current to flow in the power wires
False. For electrostatic interference NO CURRENT is required in either wire.
Electrostatic interference from a piece of equipment:
Is easily prevented by using screened cable
True. Electrostatic fields will not pass through a conductive barrier
Electrostatic interference from a piece of equipment:
Is reduced by insulating the signal leads
False. Insulation will not prevent an electrostatic field affecting the wires inside the insulation. The wires must be encased in a conductive NOT insulating layer
Electrostatic interference from a piece of equipment:
Is minimised at high frequencies
False. Would be increased at high frequency. Electrostatic interference is a form of capacitive linkage
Electrostatic interference from a piece of equipment:
Is halved by doubling the separation between signal and power leads
True. Doubling the separation, halves the field strength between the two wires.
Electromagnetic interference:
Requires the source of the interference to be drawing (using) current
True. When an alternating current is flowing an alternating magnetic field is generated around the power wire and this induces current in the signal lead.
Electromagnetic interference:
With an ECG monitor can be prevented by using screened leads
False. Screening does NOT prevent the magnetic field from affecting the signal wires.
Electromagnetic interference:
Is halved by doubling the separation between signal and power leads
False. Magnetic field strength varies as the reciprocal of the separation SQUARED.
Electromagnetic interference:
Does not affect battery powered equipment
False. Battery powered equipment is just as likely as mains powered equipment to be affected by an external magnetic field
Electromagnetic interference:
May be caused by a transformer
True. Whilst most of the huge magnetic field generated by a transformer is concentrated within its core, part of the field will lie outside and could therefore affect a nearby signal lead.
Requirements of an earth connection:
Resistance must be less than 0.5 ohm
False. Less than 0.1 ohm
Requirements of an earth connection:
Leakage current must be less than 0.5 mA (Type I equipment)
True. Part of the earth test.
Requirements of an earth connection:
Its connection at the substation must be tested regularly
False. The earth connection is the LOCAL earth and is NOT connected at or to the substation.
Requirements of an earth connection:
Must be capable of carrying a current of 25 A
True. Earth surge test requires that the local earth can carry a current of 25A for 5 seconds
Requirements of an earth connection:
Surge test must be performed at 240 Volts
False. Since the resistance of the earth must not exceed 0.1 ohm, the surge test would not require a voltage of more than 2.5 V (from ohms law).
The star point:
Is the Earth connection at the electrical substation
True. Connecting one side of the 240V supply to earth at the electricity substation creates the neutral connection
The star point:
Is connected to the Neutral wire at the electrical substation
True. Connecting one side of the 240V supply to earth at the electricity substation creates the neutral connection.
The star point:
Carries electric current back to the power station
False. Current flows between LINE and NEUTRAL wires
The star point:
Protects the user from the effects of a lightening strike
True. The substation earth (star point) provides a path for lightening to reach the ground
The star point:
Is not used in a three phase electricity supply
True. A true three phase supply does not use a neutral connection.
An earth free supply:
Increases electrical safety
True. The supply is not earth referenced. The isolating transformer means that the 240 V supply is no longer connected to the Star point, current can therefore not flow through you, via the ground to complete the circuit
An earth free supply:
Provides reduced protection from electric shock
False. Increased
An earth free supply:
Has line and neutral connections
False. Since neither supply wire is connected to ground at the substation there is no ‘neutral’ wire. ‘Neutral’ wires are only if they connect back to a ‘star point’ which is earthed.
An earth free supply:
Is required for Type II equipment
False. Type II equipment requires no earthing but is nothing to do with the type of electrical supply to the equipment.
An earth free supply:
Removes the need for a local earth connection
False. A local earth is still provided in case the ISOLATION fails because of a fault. It also has something called a Line Isolation Monitor, that is constantly checking that the supply remains earth free.
The Line Isolation Monitor:
Is required by an earth free supply
True. To warn you if a fault has compromised safety of the system
The Line Isolation Monitor:
Generates an alarm if too much current is drawn
False. Alarms if the supply has accidentally become earth referenced as the consequence of a fault.
The Line Isolation Monitor:
Generates an alarm if an earth connection is made
True. i.e. if the supply has become ‘earth referenced’.
The Line Isolation Monitor:
Switches off the supply when an electric shock occurs
False. You wish !!
The Line Isolation Monitor:
Checks that more than one phase are not connected together
False. It is checking that the supply to eg an operating theatre has not been earthed. Supply to such places is normally only one phase (therefore no other phases to be connected to).
When considering electricity:
Electrons move at close to the speed of light
False. Electron drift velocities depend on the current flowing and cross sectional area of the conductor (they are generally quite slow)
When considering electricity:
Alternating current has a mean amplitude of zero
True. Forward and reverse currents are equal
When considering electricity:
For a single phase mains supply the peak voltage is 250V.
False. 250V RMS equates to peak voltage of +/- 339V.
RMS stands for ‘root, mean, square’, and is a way of calculating the average voltage from alternating current. If you tried to calculate the average voltage from averaging the true figures you would end up with zero as they equally positive and negative. Instead you square both side to make them both positive, then take the mean, and they take the square root. Another way to do this is to divide the peak amplitude by the square root of 2 (approximately 1.414). This yields the actual, useable voltage.
When considering electricity:
Direct current is easier to switch off than alternating current
False. It is hard to switch off direct current because a continuous and therefore self sustaining arc is produced.
When considering electricity:
Current can be dissipated by an earth connection
False. Current can not be ‘dissipated’. Electrons must flow around a circuit.
In an electrical transformer:
The efficiency is approximately 60%
False. Well over 95%
In an electrical transformer:
Electrons are transferred between its primary and secondary windings
False. There is no connection between the windings. Energy is transferred by a fluctuating magnetic field
In an electrical transformer:
Changing the turns ratio can increase or decrease the output voltage
True. The ratio of primary to secondary voltage depends upon the ratio of the number of turns on primary and secondary windings.
In an electrical transformer:
When voltage is halved, the maximum current available is halved
False. If the secondary voltage is half that applied to the primary, then the secondary current is TWICE that drawn by the primary. Remember that power cannot be created by a transformer, and P = V x I. So if voltage is increased, current must be decreased by the same amount.
In an electrical transformer:
An earth connection increases efficiency
False. Nonsense
Electrical burns:
Are caused by direct current
True. And by alternating current.
Electrical burns:
Are concentrated in deep tissues
False. Are concentrated where the current density and resistance are greatest - usually at skin entry and exit points.
Electrical burns:
The size depends on the voltage applied to the tissues
True. Depends on current density (and therefore indirectly voltage) and resistance.
Electrical burns:
Depend upon the size of the current passed
True.
Electrical burns:
Only occur if the frequency is less than 100KHz
False. Frequency does not affect the direct dissipation of heat in the tissues. Diathermy works by producing local heating.
Electrical skin resistance to direct current (DC) defibrillation:
Decreases as paddle surface increases
True. Think of it as large numbers of small areas (resistances) in parallel.
Electrical skin resistance to direct current (DC) defibrillation:
Increases when electrode jelly is applied to the paddles
False. Contact resistance is decreased
Electrical skin resistance to direct current (DC) defibrillation:
Decreases as the energy (watt-seconds) delivered increases
True.
Electrical skin resistance to direct current (DC) defibrillation:
Increases as the number of shocks increases
False. Transthoracic impedance marginally decreases following repeated shocks, but this is unlikely to be clinically significant
Electrical skin resistance to direct current (DC) defibrillation:
Decreases with an increase in paddle pressure
True. Increasing paddle pressure increases contact area and decreases resistance.
Direct current:
Flows in one direction
True. By definition
Direct current:
Is constant in magnitude
False. It can vary in magnitude and even be discontinuous as long as it does not reverse direction
Direct current:
Can be produced from alternating current
True. By placing a diode (electrical one way valve) in the wire
Direct current:
Is not harmful to the tissues
False. Power is still dissipated in the tissues and ions (the charge carriers) still move.
Direct current:
Will cause electrostatic interference
False. Electrostatic interference requires a ALTERNATING voltage to be present
When considering the classification of electrical equipment:
Type II apparatus requires an earth connection
False. Double insulated apparatus has TWO physical barriers between the electrically applied part (the part of the apparatus connected to the mains) and the user.
When considering the classification of electrical equipment:
The maximum earth leakage current for type B(F) equipment is 500uA
True. Type I equipment - leakage current must not exceed 0.5mA (500uA). In type II equipment where it is not earthed however the maximum is 0.1mA (100uA).
When considering the classification of electrical equipment:
Type I equipment is internally powered.
False. Type III is internally powered.
When considering the classification of electrical equipment:
For type C(F) equipment the (F) signifies Earth free
False. The F suffix states that the patient applied part (the bit of the equipment which is connected to the patient) is ‘FLOATING’, i.e. is electrically isolated from the rest of the apparatus.
When considering the classification of electrical equipment:
Type III equipment may be used whilst charging
False. Type III equipment is ‘internally powered’, if connected to an external power supply, for example whilst charging, it is no longer internally powered and the classification would change to that of the charger.
The fuse in the electrical supply to medical equipment:
Should be replaced after 1000 hours’ service
False. There is no requirement for regular replacement
The fuse in the electrical supply to medical equipment:
Should be of the quick blow type
False. The fuse characteristics are determined by the electrical supply requirements of the apparatus
The fuse in the electrical supply to medical equipment:
Provides protection from electric shock
True. In a major equipment fault the fuse will by blowing limit the duration of electric shock and therefore minimise its biological effect
The fuse in the electrical supply to medical equipment:
If placed in the neutral wire enhances electrical safety
False. It would be much more dangerous
The fuse in the electrical supply to medical equipment:
Can be replaced by an earth leakage circuit breaker (RCCD)
False. Whilst this would enhance safety, the equipment would not be protected should a fault develop.
When considering the electrical supply to medical apparatus:
The local earth wire is brown
False. Green and yellow
When considering the electrical supply to medical apparatus:
The line wire is red
False. Brown
When considering the electrical supply to medical apparatus:
The fuse should be chosen to limit leakage current to a safe value
False. Fuse is chosen to allow the apparatus to draw the power it requires to operate
When considering the electrical supply to medical apparatus:
Two pin plugs avoid the risk of earth leakage
False. Earth leakage currents would be no less likely. Without a local earth connection they would be more dangerous
When considering the electrical supply to medical apparatus:
Use of an extension lead compromises electrical safety
True. Even IF included in ‘earth continuity’ and ‘earth surge’ tests, increased contact resistance would increase shock risk.
Type III apparatus:
Requires three wires, Line, neutral and earth
False. It is internally powered.
Type III apparatus:
The earth leakage current must not exceed 0.5mA (500uA)
False. Has no mains connection and therefore leakage current is not possible.
Type III apparatus:
Must not be directly connected to a patient
False. e.g. an internally (battery) powered nerve stimulator
Type III apparatus:
Can not act as the source of leakage current to a patient
True. Has no mains connection and therefore leakage current is not possible.
Type III apparatus:
Must have a fuse of less than 1 Amp
False. It has NO mains connection.
The following statements are correct regarding basic electrical quantities and units:
The coulomb is a unit of electrical charge equivalent to 6.24 x 10^18 electrons
True.
The following statements are correct regarding basic electrical quantities and units:
The coulomb is a base SI unit
False. The coulomb is SI unit of charge and is a derived unit. It’s base unit is A.s (ie the amount of electricity carried by a 1-ampere current in one second).
The following statements are correct regarding basic electrical quantities and units:
A 3 kW electrical appliance (running on UK mains voltage) would require a 5 amp fuse
False. Power = Voltage x Current. The load of 3kW appliance running at 240 Volts is 3000/240, i.e. 12.5A, and therefore will require 13A fuse.
The following statements are correct regarding basic electrical quantities and units:
The definition of 1 ampere is the flow of 1 coulomb of charge per second through any cross-sectional area of the conductor.
True. A = C/s, hence why the base unit of Q (charge with units being coulombs, C) is A.s.
The following statements are correct regarding basic electrical quantities and units:
The resistance of a conductor is a constant value that is not influenced by other factors
False. Resistance of a conductor increases with length and decreases with cross-sectional area. Each material used as a conductor has its own resistivity, which is not based on other factors.
The following statements are correct regarding capacitors and their capacitance:
Capacitors used in defibrillators typically have a capacitance of greater than or equal to 1 farad
False. Capacitors used in defibrillators are of very low value usually in micro farads.
The following statements are correct regarding capacitors and their capacitance:
Increasing the distance between the plates of a capacitor increases its capacitance
False. Increasing the distance between the plates of a capacitor decreases its capacitance. For a simple capacitor, the capacitance is proportional to the area over which the plates overlap and inversely proportional to their distance apart.
The following statements are correct regarding capacitors and their capacitance:
The introduction of a dielectric between the plates increases the capacitance
True.
The following statements are correct regarding capacitors and their capacitance:
The stored energy of a capacitor is given by the formula: E = 1/2QV^2
False. The stored energy of a capacitor is given by the formula: E = 1/2CV^2
where C is capacitance in farads
As opposed to the equation given in the stem where Q is charge in coulombs.
The following statements are correct regarding capacitors and their capacitance:
Capacitors can be directly charged using alternating current
False. Alternating current need to be converted to direct current to charge capacitors.
