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MARKING GUIDELINE -1-
ELECTRICAL TRADE THEORY N3
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NATIONAL CERTIFICATE
ELECTRICAL TRADE THEORY N3
2 AUGUST 2019
This marking guideline consists of 8 pages.
MARKING GUIDELINE
Page 2 of 8
MARKING GUIDELINE -2-
ELECTRICAL TRADE THEORY N3
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QUESTION 1: DOMESTIC APPLIANCES
1.1
(2)
1.2
(Any 4 × 1) (4)
1.3 Heat causes the bimetal strip to bend. The temperature-adjusting cam
increases the distance and the bimetal strip flexes, opening the contacts. (2)
1.4 There could be:
An insulation fault in the flexible cord from the plug to the iron
An insulation fault between the element and the casing of the iron
An internal insulation fault between earth and the current-carrying parts in
the switching circuit of the iron (Any 2 × 1) (2)
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L N E
Spring steel
Temperature-adjusting cam
Control knob
Heating element
Bimetal strip
Snap-action contacts
Page 3 of 8
MARKING GUIDELINE -3-
ELECTRICAL TRADE THEORY N3
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QUESTION 2: PROTECTION
2.1 2.1.1
2.1.2
2.1.3
2.1.4
2.1.5
2.1.6
2.1.7
Oil-filled cylinder
Solenoid (coil)
Iron armature
Trip switch
Movement operates tripping mechanism
Spring
Iron piston
(7 × 1) (7)
2.2 The piston is attracted into the coil centre because of the magnetic field setup
by the current overload. Now the armature is attracted and the mechanical
link opens the contacts. This opens the circuit and the current flow stops. (3)
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QUESTION 3: ILLUMINATION
3.1 It provides the voltage surge for starting.
It limits the current to the operating value of the lamps. (2)
3.2 It reduces the electrical shock hazard.
The fixed base pin acts as a switch breaking the circuit to the ballast when
the lamp is removed. (2)
3.3 3.3.1 Street lighting
Flood lighting
Lighting of industrial premises (Any 2 × 1) (2)
3.3.2 Streetlighting
Security Lighting
Highways / Airport runways
(Any 2 × 1) (2)
3.3.3 Electrical appliances, such as stoves, fridges and heaters
Control panels where space is limited (2)
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