Worksheets3005 410 MEN, SELV, PELV Electrical Protection 1
Total questions: 20
Worksheet time: 7mins
What is not one of the 3 main categories of faults that we need to protect for?
Earth Leakage faults
Over current
Under current
short circuits
Current finds a path of very little ________ which leads to high current.
Inductance
Current
Capacitance
Resistance
Over current is defined as ........
Current that is bigger than the rated current of the equipment
Current that exceeds the rating of a standard 10 amp socket oulet
As per As/NZS3000 2007 2.4.3.1 any current exceeding 63 amps
Current that is more than that defined in AS/NZS 3000: 2007 4.2.1 (a)
Earth leakage current is defined as .......
A small amount of voltage that is lost or leaked to earth
A level of current that can be detected by an RCD
The standing leakage current from induction motors
A small amount of current that is lost or leaked to earth
The maximum disconnection time (230/400 supply voltage) in the event of a fault shall not exceed ___ seconds for hand held electrical equipment.
0.3
0.4
0.5
5
What problem does earth leakage current not cause?
Reduces the efficiency of the installation due to lost energy
Reduces the safety factor and increases the chance of an electric shock
Causes nuisance tripping of MCB's
Could cause a fire in flammable situations
Electrical faults can cause more _______ to flow than the system was designed for.
Current
Voltage
Electrons
Resistance
Electromechanical energy is when electrical energy is converted into __________ energy
Electrical
Heat
Kinetic
Mechanical
With electric shocks the effect (damage caused) to the body will depend on the size of _________ and time that it flows
voltage
current
MCB
capacitor
Disconnection times of up to 5 seconds are permitted for circuits not directly supplying portable equipment or hand-held equipment because:
Faults in such circuits are more likely
There is more likelihood of being in contact with equipment during a fault
Equipment is usually not gripped and can be released easily
Touch voltages are expected to exceed the time/touch voltage relationship
An electric shock is when any voltage flows through the body
True
False
The current uses the body as a high resistance path to earth and it flows through the body
True
False
The causes of overvoltage in an elctrical system is not normally affected by what?
switching operations
lightning
resonant phenomena
overloaded circuits
Electrical protection shall be selected, installed and protected such that the equipment will ........
not obstruct escape routes either directly or by the products of combustion
contribute to or propagate a fire
attain a temperature high enough to ignite adjacent material
adversly affect means of egress from a structure
According to AS/NZS 3000 2007 the touch voltage limits for other than hand held equipment are ........
230v AC or 325v ripple free DC
50v AC or 120v ripple free DC
Touch volatge limits do not apply to other than hand held equipment
25v AC or 60v ripple free DC
The maximum disconnect time for subcircuits supplying fixed or stationary equipment is ______ milliseconds
300
400
500
5000
Earth leakage current is normally measured in ..........
V
mA
A
KVA
Double insulated power tools are classed as class 2 equipment
True
False
If the curent in a cable was doubled by what percentage would the heat increase to
400%
200%
100%
25%
what is the prospective short circuit current of a 1KVA single pase transformer with an impedance of 5%
21.73A
86.95A
1763A
5000A
