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WorksheetsElectrical Protection 4
Total questions: 20
Worksheet time: 10mins
Electrical cordination is provided when the protective device _______ ______ the fault is activated
closest to
farthest from
Which of the following electrical faults do we not need to provide protection for
short circuits
overcurrent
open circuit
earth leakage
Which type of circuit breaker will operate between 3 and 5 times the circuit breaker current rating
Type A
Type B
Type C
Type D
What type of energy may be dissapated as a result of a short circuit
Sound energy
Electromechanical energy
Light energy
Chemical energy
The rated current of a fuse is the _________ current a protective device can carry cotinuously without deterioration
short circuit
maximum
minimum
leakage
________ ________ is the maximum current that a circuit breaker or fuse can safely interupt.
Category of duty
Breaking capacity
Which one of the following is a reason why rewireable (SERF) fuses are no longer permitted to be used for new installations
They are expensive to replace
They do not comply with the regulations for safety reasons
They are not as aesthetically pleasing as other types of fuses
The PSCC rating of the fuses exceeds the capability of the power network
Close excess current protection is .............
The maximum current a device can carry continuously without deterioration
The maximum fault current that a protective device can safely stop flowing
protection that will operate within 4 hours at 1.5 times the designed load current of the circuit it protects
a rating used to show the type of voltage and the rupturing/breaking capacity of a fuse
What form of energy may be dissapated as a result of a short circuit fault
Heat energy
Chemical energy
Light energy
Sound energy
What description best describes a SERF protection device
Thermal and magnetic operating devices are housed in a sealed plastice case
Silver fuse element surrounded by a filler and enclosed in a ceramic body
Electronic monitoring circuits housed in a sealed plastic case
Consists of an alloy wire containg 63% tin and 37% lead and having a circular section held in a ceramic body
What description best describes how a HRC fuse operates
When a sustained overload occurs, the element will generate heat at a faster rate than the heat can be passed to the filler. If the overload persists, the element will reach its melting point and open.
Monitors the imbalance in L & N current and opens the circuit
Has a thermal (bi-metal) and magnetic (solenoid) operating mode
Current flow above its rated value causes the wire to break and open the circuit
Which one of the following is a reason why rewireable (SERF) fuses are no longer permitted to be used for new installations
They are not as aesthetically pleasing as other types of fuses
The PSCC rating of the fuse far exceeds the capability of the power network
They are a fire risk as the wrong element may be fitted deliberately or by accident
The porcelain base and holder are fragile and pose a safety risk to someone removing or replacing the fuse
What description best describes the basic operating principle of an RCD under no fault conditions
The normal sensor coil back emf opposes the induced emf, allowing the circuit breaker to remain closed and not affecting the circuit.
No fault condition causes the live and neutral current to unbalance the sensing coil, tripping the mechanism and isolating the circuit.
No imbalance of current ensures no sensor coil voltage is induced and normal operation of the tripping mechanism.
A no fault situation results in a normal imbalance of currents, inducing a small sensor coil voltage too small to trip the mechanism.
What description best describes what a RCBO device is
A type of RCD that automatically trips on detection of an inbalance of current between the phase and earth
A RCD device that detects an inbalance of current between the phase and neutral conductors
A RCD device that not only detects an imbalance of current between the phase and neutral but also earth leakage currents
A RCD device that not only detects and inbalance of current between phase and neutral but also overload
What type of device fits the following description "A device comprising a plug, a residual current device and one or more socket-outlets (or a provision for connection)"
RCCB
RCBO
PRCD
SRCD
In terms of sensitivity and Type, what is the most appropriate RCD for additional personal protection within a domestic premises.
30 mA sensitivity Type A
10 mA sensitivity Type A
30 mA sensitivity Type AC
10 mA sensitivity Type AC
In Schools up to year 8, 10mA RCD protection is required. What is the maximum operating time of the RCD in this environment?
30mS
40mS
100mS
300mS
What description best describes the operation of an RCD under fault conditons
An imbalance of live and neutral currents results in a sensor coil voltage tripping the circuit breaker and isolating the circuit.
In a fault to earth the imbalance in current will induce a voltage in the neutral conductor, tripping the circuit breaker and disconnecting the circuit.
An uneven current in the phase and neutral conductors caused by short circuit load resistor will induce a sense coil voltage and trip the mechanism.
An RCD with a live and neutral open circuit fault will cause an imbalance and induce a sense coil voltage, and trip the mechanism.
What would the tripping factor be of a 20A MCB if the minimum tripping current is 25A
0.8
1.25
1.33
1.5
If a 230 V circuit has an insulation resistance value of 50 MΩ, what is the leakage current in micro-amps?
23.6𝜇A
2.3𝜇A
4.6𝜇A
21.7𝜇A
