EWRB THEORY COMPREHENSIVE
SCRIPT UPDATED QUESTIONS WITH
CORRECT ANSWERS
◉ how to test and appliance before returning to service Answer:
visual, insulation test, earth continuity, polarity
◉ difference between continuity and resistance testing Answer:
continuity checks if path exists and resistance measures exact value
◉ why is the neutral earthed multiple times in the men system
Answer: provides multiple fault paths
◉ main advantage of men Answer: reduced shock risk
◉ where is the neutral-earthed multiple times bond located in men
system Answer: at the switchboard
◉ what happens if the earth conductor breaks Answer: risk of
electric shock
◉ how does the men system protect against shock Answer: RCD
trips on leakage
,◉ colour of the earth conductor in nz Answer: green and yellow
◉ potential fault without men maintenance Answer: dangerous
touch voltage
◉ how does men ensure fast RCD trippping Answer: by providing
low impedance fault path
◉ why are multiple earths used Answer: improve reliability and
reduce voltage rise
◉ Difference between TN and TT systems
TT has local earth and TN has men
TN is cheaper
TN always uses fuses
TT has not protection Answer: TT has local earth and TN has men
◉ how is fault current calculated in men system Answer: using ohms
law and network resistance
◉ which device disconnects circuits during men faults Answer: fuses
and MCBs
,◉ what happens if neutral is disconnected but earth intact Answer:
dangerous voltages may appear
◉ what's the purpose of earthing electrodes Answer: provides safe
path for fault currents
◉ why must men system be regularly inspected Answer: to censure
correct operation and safety
◉ how does men reduce touch voltages ? Answer: by providing a
low resistance path to earth
◉ where is men system implemented Answer: nz residential and
industrial supply
◉ how are earth bonds tested Answer: measure resistance(should
be low)
◉ purpose of star-delta starter
reduce starting current
increase voltage
reverse rotation
reduce efficiency Answer: reduce starting current
, ◉ why does star reduce current draw
reduces line voltage per winding
reduces speed
reduces power factor
increases torque Answer: reduces line voltage per winding
◉ what happens with phase loss
motor runs normally
motor overheats and may fail
motor slows slightly
nothing Answer: motor overheats and may fail
◉ describe delta connection characteristics
low voltage per winding
full line voltage, high torque
only used in single phase
reduces speed Answer: full line voltage, high torque
◉ causes of unbalanced currents Answer: unequal voltage supply,
uneven load
SCRIPT UPDATED QUESTIONS WITH
CORRECT ANSWERS
◉ how to test and appliance before returning to service Answer:
visual, insulation test, earth continuity, polarity
◉ difference between continuity and resistance testing Answer:
continuity checks if path exists and resistance measures exact value
◉ why is the neutral earthed multiple times in the men system
Answer: provides multiple fault paths
◉ main advantage of men Answer: reduced shock risk
◉ where is the neutral-earthed multiple times bond located in men
system Answer: at the switchboard
◉ what happens if the earth conductor breaks Answer: risk of
electric shock
◉ how does the men system protect against shock Answer: RCD
trips on leakage
,◉ colour of the earth conductor in nz Answer: green and yellow
◉ potential fault without men maintenance Answer: dangerous
touch voltage
◉ how does men ensure fast RCD trippping Answer: by providing
low impedance fault path
◉ why are multiple earths used Answer: improve reliability and
reduce voltage rise
◉ Difference between TN and TT systems
TT has local earth and TN has men
TN is cheaper
TN always uses fuses
TT has not protection Answer: TT has local earth and TN has men
◉ how is fault current calculated in men system Answer: using ohms
law and network resistance
◉ which device disconnects circuits during men faults Answer: fuses
and MCBs
,◉ what happens if neutral is disconnected but earth intact Answer:
dangerous voltages may appear
◉ what's the purpose of earthing electrodes Answer: provides safe
path for fault currents
◉ why must men system be regularly inspected Answer: to censure
correct operation and safety
◉ how does men reduce touch voltages ? Answer: by providing a
low resistance path to earth
◉ where is men system implemented Answer: nz residential and
industrial supply
◉ how are earth bonds tested Answer: measure resistance(should
be low)
◉ purpose of star-delta starter
reduce starting current
increase voltage
reverse rotation
reduce efficiency Answer: reduce starting current
, ◉ why does star reduce current draw
reduces line voltage per winding
reduces speed
reduces power factor
increases torque Answer: reduces line voltage per winding
◉ what happens with phase loss
motor runs normally
motor overheats and may fail
motor slows slightly
nothing Answer: motor overheats and may fail
◉ describe delta connection characteristics
low voltage per winding
full line voltage, high torque
only used in single phase
reduces speed Answer: full line voltage, high torque
◉ causes of unbalanced currents Answer: unequal voltage supply,
uneven load
