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WorksheetsElectrical Protection 3
Total questions: 20
Worksheet time: 10mins
What statement best describes the construction of a fusible link
A metal encased device that detects overcurrent in heating appliances
a metal alloy element enclosed in a small metal canister with 2 leads
a fuse in metal surrounded by quartz silica sand
a porcelain type fuse used in heating appliances
Fusible links are designed to interupt current flow when the current gets too high
True
False
"HRC" stand for ...
High rupturing capacity
High rupturing current
High resistance capacity
High resisitance current
The ceramic fuse barrel of a HRC fuse has good _______________ characteristics
Insulation and strength
looks and strength
mechanical strength and thermal
insulation and thermal
The filler in HRC fuses is made of graded silica which has good ....
thermal characteristics
arc extinguishing properties
insulation properties
thermal conductivity
HRC fuses are used in installations where higher prospective short circuit voltages are present
True
false
A MCB trips by what type of action during overcurrent
Solenoid coil action
thermal
magnetic
bi -metal
What element is NOT part of the construction of an MCB?
Arc chamber
Bi-metal
Reset lever
Test button
A short circuit will operate a MCB by magnetic action
True
False
A MCB operating at twice the rated current of the device will trip by _______ action
Magnetic
timer
Thermal
A combination of thermal and magnetic
The fuse element of a HRC fuse is made up of a specially shaped material made of ...........
Copper
Copper/titanium
silver
Copper/silver
RCD's are protective devices that interupt the supply current when .......
an overcurrent is detected
the touch volatge exceeds 50v AC
the thermal or magnetic mechanism trips
a set leakage current is detected
An RCD wil trip instantly when there is a short between phase and neutral
True
False
The sensitivity of an RCD is the maximum inbalance in current between phase & neutral an RCD will allow before it will trip
True
False
The sensitivity of a type 1 RCD is .........
<300ms
10mA
30mA
<40ms
30mA RCD's are designed to operate before fibrillation of the heart occurs.
True
False
An RCCB is a RCD combined with a MCB in one device.
True
False
An RCD works by detecting ..........
Leakage current flowing in the protective earthing conductor
a higher current in the neutral than in the phase conductor
a higher current in the phase conductor than the neutral
an imbalance of current between the neutral and earth conductors
RCD's are not required when double insulated power tools are being used.
True
False
The type of sensing coil in an RCD is a ..........
Inductive transformer coil
Capacitive leakage sensing coil
Magnetic sensing coil
Toroidal cored sensing coil
