Power Systems Revision - Grade 10 Term 3 & 4 (2025) – Domestic Installations & Principles of Magnetism

Flashcards covering key concepts from Domestic Installations and Principles of Magnetism as presented in the revision booklet.

What are the three stages of electricity supply from the power station to the consumer?

Generation, transmission, and distribution.

What does SANS stand for?

South African National Standard.

Explain the difference between a Class I and a Class II appliance.

Class I: has basic insulation and an earth (earthing) terminal. Class II: has double insulation throughout and no earth terminal.

Name four requirements when wiring a distribution board (any four).

1) The main supply cable must have the correct cross-sectional size. 2) Sub-circuits must have appropriate cross-sections. 3) Switchgear must meet current ratings/regulations. 4) Live and neutral must be fed through the main circuit breaker.

Give ONE portable appliance and ONE fixed appliance as examples.

Portable: Fan. Fixed: Stove.

Name TWO places where a Distribution Board may not be mounted.

In a bathroom; Above a fixed cooking appliance.

List the seven common labels in a typical distribution board sketch.

1) Live (L) supply conductor 2) Miniature circuit breakers (MCBs) 3) Residual current device (RCD) / earth leakage 4) Main circuit breaker 5) Earth spike 6) Neutral bus bar 7) Earth bus bar.

Complete the table: Maximum protection rating vs maximum cross-sectional area for conductors.

10 A → 1.5 mm2; 20 A → 2.5 mm2; 40 A → 6 mm2.

Explain the difference between a Circuit Breaker and a fuse.

A circuit breaker can be reset after tripping; a fuse melts and must be replaced.

Name the two types of MCBs available.

Electromagnetic type and Thermal type.

Name the three standard colours for Neutral, Earth, and Live in a domestic installation.

Neutral: Black; Earth: Green/Yellow; Live: Red.

Explain the use of bending spring and fish tape in domestic installations.

Bending spring is used to bend PVC conduit into angles; Fish tape is used to route new wiring through conduits.

Explain the function of the Earth Spike.

An earth spike provides a connection to the earth (ground) to carry leakage currents back to the supplier; it's driven into the ground to form a grounding system.

What is the Insulation Resistance Tester used for in domestic installations?

To test insulation resistance between conductors and between conductors and earth.

Define an Inductor.

A coil of wire that stores energy in its surrounding magnetic field.

What is the symbol for an Inductor?

A coil symbol (often labeled with L).

If L2 = 50 mH and L3 = 60 mH and LTOT = 150 mH, what is L1?

L1 = 40 mH (LTOT = L1 + L2 + L3; 150 = L1 + 50 + 60 → L1 = 40).

Explain the function of a Relay.

To isolate two parts of a circuit and allow one circuit to switch another (eg a 12 V coil switching a 230 V mains circuit).

What are the two main parts of a relay?

The coil and the switch contacts.

Give TWO practical applications of a relay.

Isolating low-voltage/DC circuits from high-voltage AC circuits; control in automation/PLC systems and motor control circuits.

What are the three main parts of a DC motor?

Armature/Rotor, Field coils or Permanent magnet, Brushes.

What material are the brushes made from?

Graphite/Carbon.

Explain the function of the brushes.

To make electrical contact with the stationary external circuit by sliding on the surface of the commutator.

How can you change the direction of rotation of a DC motor?

By reversing the supply polarity—swap live and neutral.

What is the purpose of a two-way lighting system diagram in domestic installations?

To show how a light can be controlled from two locations using two switches.

What are Magnetic Flux Lines?

Invisible lines that represent the magnetic field around a magnet.

Name THREE characteristics of magnetic flux lines.

They are continuous/closed paths; they never cross; outside a magnet they go from North to South (inside, from South to North).

State the two laws of magnets.

Like poles repel; Unlike poles attract.

Define Magnetic Flux and Magnetic Flux Density.

Magnetic Flux: invisible lines around a magnet. Magnetic Flux Density: concentration of flux lines per unit area.

State Maxwell’s Right-Hand Rule.

Hold the conductor with the right hand: thumb in the direction of current; fingers show the direction of the magnetic field.

In a current-carrying conductor, what direction does the magnetic field circulate according to the corkscrew rule?

The magnetic field circulates clockwise around the conductor for the indicated current direction.