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WorksheetsFault finding NETK3/7
Total questions: 35
Worksheet time: 53mins
An operative carrying out fault diagnosis would not need to be familiar with:
supply earthing system
schedule of test results
repair cost
voltage present
Which of the following would not be required in a fault finding sequence:
time repair will take
safe isolation
testing
analysis of results
A continuity test as part of fault diagnosis would be carried out with which instrument:
earth-fault loop impedance tester
high resistance ohmmeter
low resistance ohmmeter
RCD tester
A loose termination could cause the following
short circuit between live conductors
overcurrent
arcing
operation of the protective device
The guidance for test leads used on instruments is contained in
BS 7671
EAWR
HASAWA
GS38
Which dead test would be carried out during intial fault diagnosis
RCD test
insulation resistance
functional
earth-fault loop impedance
Whilst fault finding you check and discover the BS 3036 fuse protecting the circuit has ruptured with globules of copper spattered over the holder together with black carbon powder. The most likely fault would be:
short circuit
open circuit
loose termination
broken conductor
Whilst fault finding, you check and discover the BS 3036 fuse protecting the circuit has melted in the middle only. The most likely fault would be:
open circuit
short circuit
loose termination
overload
A result of >100Ω on a continuity test would indicate what type of fault:
none
an insulation failure
open circuit
short circuit
An RCD would protect against the following fault:
open circuit
overcurrent
short circuit between live conductors
short circuit between live conductors and earth
The definition of isolation is
Functional switching for normal operation
Single pole devices connected in the phase conductor
Removing from every source of electrical energy
Isolating equipment from general mass of earth
An approved voltage indicator should be used to
Measure R1+R2
Prove a circuit is dead before work begins
Measure appropriate voltage
Prove a circuit is live before work begins
The item shown in the photo should be used in what process?
Voltage measurement
Socket polarity
Calibration checks
Safe isolation
Which of the following is the most likely of implications caused from an exposed terminal?
Electric shock to a person or livestock
MCB operate
RCD Operates
Main Cut off fuse operates
The safest method of ensuring that a system is safe to work on is?
Follow the safe isolation procedure
Isolate the installation at the main cut-out
Use a fluke volt stick before you begin
Place barriers at the distribution boards
What is the benefit of using multi-hasp type padlock when isolating and locking off a circuit for maintenance?
More than one circuit can be isolated at any one time
Any single operative can make the circuit live once they have completed their task
A circuit can only be made dead if all the operatives use locks
More than one person can work on the circuit safely
Which of the following would be most important to be discussed with the client prior to any fault diagnostics being carried out.
Cost of the work
Isolation timing
The Earthing system
The breaking capacity of the main protective device
Which of the following could cause an SPD to operate
Short circuit
Lightning stikes in the area
Overload in the circuit
A damaged light switch
Which of the following would be the most likely cause of the final light in a lighting circuit not working when the other lights do
Short Circuit at the origin
Open Circuit at the origin
Open circuit in the last leg of the cable
Short Circuit in the last leg of the cable
Which logical stage should be carried first before carrying out fault diagnosis
Gather information on Symptoms
Rectify the work
Safe isolation
Functional testing
Which of the following tests is performed if a broken cable is suspected?
Prospective Fault Current
Insulation Resistance
Continuity of Ring Final Conductors
Earth Fault Loop Impedance
Several test instruments are used on an installation, which of the following would be most likely to give a reading of 2.5kA?
Low resistance ohmmeter
Prospective fault current
Insulation resistance tester
RCD tester
The main reason for the cross connecting the conductors during the ring final circuit test and not just relying on end to end reading is?
To record the values in the R1+R2 box at the same time
A more accurate R2 reading can be obtained
To ensure that the circuit is clear of short circuits or earth faults
To detect any interconnections in the circuit
The accessory pictured is often used in testing when conducting test using what particular method?
Test method 2
Test method 1
Continuity of ring final conductors
Test method 3
The Ze is to be measured as part of the initial verification process, what instrument should be used for this task?
An earth fault loop impedance tester
An insulation resistance tester
An RCD tester
A low resistance ohmmeter
The following readings were taken on a test performed on a ring final circuit, Line to Line 0.8 Ω Neutral to Neutral 0.8 Ω cpc to cpc 0.8 Ω . What would be the expected reading between line and cpc at each socket outlet?
1.6 Ω
0.4 Ω
0.8 Ω
0.2 Ω
What is the importance of verifying readings obtained with those listed within BS7671 and associated documents?
The circuit is safe and within design parameters
The circuit protection does not operate accidentally without warning
The instrument is functioning correctly and within stated tolerances
The instrument conforms to BS EN 61010
If two bonding conductors or equal length were connected in parallel the resistance would
Increase
Double
Not change
Halve
During a continuity of Ring final conductors test, 10 Sockets give a R1+R2 reading of 0.68 Ω, but one socket gives a reading of 0.92 Ω. What might that indicate?
A spur on the circuit
A trapped cpc in the back of the box
A short circuit
A high resistance fault
A polarity test is conducted to verify that
There is no breakdown of the insulation of the conductor
The resistance is sufficiently low to operate the protective device within the specified time
The circuit protection will operate within a pre-determined time
Every protective and single pole device is connected in the line conductor only
If 3 conductors equal in length and with a resistance of 1.5 Ω are connected in parallel, what is the total resistance?
4.5 Ω
0.5 Ω
2 Ω
15 Ω
If a copper conductor was doubled in length, the resistance would
Halve
Double
Stay the same
Quadruple
What is the formula for calculating earth fault loop impedance?
Zs = Ze-(R1+R2)
Zs = Ze+(R1+R2)
Ze = Zs-(R1+R2)
Zs = Zex(R1+R2)
An RCD within a domestic is tripping intermittently, the most likely cause for this will be,
a faulty appliance that is still plugged in
a short circuit fault
an overload
a transient voltage
In the first instance which sense would most likely detect a faulty bearing on
an air conditioning unit
sight
taste
hearing
sixth
