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Worksheets3005 411 MEN, SELV, PELV Electrical Protection 2
Total questions: 20
Worksheet time: 7mins
What problem does earth leakage not cause?
Reduces the efficiency of the installation due to list energy
Reduces the safety factor and increases the chance of electric shock
Causes nuisance tripping of MCB's
Could cause a fire in flammable situations
What does not constitute basic electrical protection?
Extra low voltage
Protection by insulation
Protection by RCD's
Protection by obstacles
Which of the following does not provide fault protection?
Electrical separation
Class 1 equipment
Automatic disconnection
Fault current limiting
Electromechanical energy is when electrical energy is converted into ___________ energy.
Electrical
Heat
Kinetic
Mechanical
What is the prospective short circuit current of a 2KVA 1 phase transformer with an impedance of 6%
100 Amps
173.9 Amps
144.83 Amps
121.73 Amps
The current uses the body as a high resistance path to earth and it flows through the body
True
False
The standard sets out 4 ways to provide fault protection. What is not one of the 4 ways from the list below?
Automatic disconnection
Electrical separation
Class 1 equipment
Fault current limiting
Impedance is the overall opposition to current flow in an AC circuit. What does not form part of the total impedance?
Resistance
Capacitive reactance
Inductive reactance
Resistive reactance
The impedance of a circuit needs to be kept low as possible so that .....
large amounts of voltage will around the fault loop
the touch voltage is as high as possible to trip the protective device
large amounts of current will flow back to earth
large amounts of current will flow around the fault loop
Automatic disconnection of the supply is intended to limit the touch voltage arising between conductive parts during a fault.
True
False
According to the standard protection devices are to be _______ reclosing devices.
automatic
self
non-automatic
compliant
in the language of circuit protection "rated current" is ......
The current that the protective device is rated to carry continuously
The rated current that the divice is rated to carry for up to 4 hours
The maximum fault current that a protective device can safely stop flowing
The maximum current that a device is rated to operate at with out a problem
In the language of circuit protection the "rupturing capacity" of a device is .....
The highest fault current that can flow through a protective device
The maximum voltage that a protective device is designed to operate at
The current that a protective device is rated to carry continuously
The maximum fault current that a protective device can safley stop flowing
In the language of circuit protection the "fusing current" is .....
The minimum current that will blow the fuse
The maximum current that the fuse will carry before blowing
The minimum current the will trip the circuit breaker
The ratio between the fusing current and the rated current of the fuse.
In the language of circuit protection "discrimination" is ......
when only the main circuit protection is affected and not the sub-circuits
when proetction is planned so only part of a supply is shut down
the difference between primary and secondary protection
the hierarchy between MCB's and RCD's
A class R fuse has a "fusing factor of between ....
1.1 - 1.25
1.25 - 1.5
1.5 - 1.75
1.75 - 2.5
A protection device that does interupt a supply current within 4 hours at 1.5 times the rated current is classed as .....
providing close excess current protection
providing course excess current protection
not providing close excess current protection
a semi enclosed rewirable fuse
A "HRC" fuse provides .....
close excess current protection
course excess current protection
close or course excess current protection
close protection for earth leakage faults
the acronym "SERF" stands for ....
single event rewirable fuse
semi- eliptical round fuse
single event round fuse
semi enclosed rewirable fuse
The purpose of a cartridge fuse is to ....
allow easy rewiring of the fuse in the event of failure
provide close excess current protection
contain the copper splatter when the fuse blows
allow easy visual indication of when the fuse has blown
