N1 Electrical Trade Theory Practice Flashcards

Comprehensive vocabulary flashcards covering safety, electrical theory, magnetism, AC/DC sources, instruments, and wiring based on the N1 Electrical Trade Theory syllabus.

SANS 10142-1

The South African National Standard for 'The wiring of premises', which provides safety requirements for electrical installations.

Live Parts

Includes the neutral conductor and any conductive parts connected to it that are at an electrical potential to earth.

Proper Earthing

The most important safety precaution to prevent electrical shock in equipment.

Coiled Extension Cords

Components that are dangerous because they can overheat as the heat generated by the current cannot be dissipated effectively.

Arc-Eyes

A painful eye condition resulting from exposure to ultra-violet rays produced during electric arc welding.

Locking Out

A system of control involving a physical lock (such as a gang lock) to ensure no unauthorized person can energize a circuit while someone is working on it.

Flame-proofing

A requirement for electrical equipment used in locations where flammable or explosive substances are present, preventing the ignition of surroundings during normal operation or breakdown.

Interlock Switches

Safety switches or contacts included in a circuit to cause it to open in the event of an incorrect operation or to ensure a specific sequence of operations.

No-Volt Coil

A component included in motor starters to ensure the circuit opens if the supply voltage fails, preventing unexpected restarting.

Switch-Disconnector

A mechanical switching device that, in the open position, satisfies the isolating requirements for an on-load isolator.

Housekeeping

The practice of keeping working spaces and walkways clean, unobstructed, and skid-free to maintain a safe working environment.

Triangular Symbolic Safety Sign

A sign with a black border and yellow centre that serves as a warning against hazards like electricity or flammable substances.

Blue Disc Symbolic Safety Sign

A mandatory sign indicating that specific protective equipment (like goggles or hard hats) must be worn.

Class A Fire

Fires involving ordinary solid combustible materials such as wood, paper, rubber, and plastics.

Class B Fire

Fires involving flammable liquids such as petrol, paraffin, benzene, and oils.

Class C Fire

Fires occurring in the vicinity of live electrical conductors or appliances.

Atom

The basic structure of matter composed of a nucleus (protons and neutrons) and orbiting electrons.

Conductor

A substance, characterized by having free electrons, through which an electrical current can flow easily.

Electric Current ($I$)

The movement of electrons in a specific direction through a material, measured in amperes ($A$).

Potential Difference ($V$)

The electrical pressure which causes current to flow between two points in a circuit, measured in volts ($V$).

Electromotive Force (emf)

The force that maintains the potential difference while a current is flowing.

Resistance ($R$)

The opposition offered to the flow of electric current, measured in ohms ($\Omega$).

Insulator

A substance that prevents the flow of electric current because it has no free electrons.

Ohm's Law

The principle stating that the current flowing in a circuit is proportional to the applied voltage and inversely proportional to the resistance: $I = \frac{V}{R}$.

Joule's Law

The principle stating that the heat ($Q$) generated in a circuit is proportional to the square of the current, the resistance, and the time: $Q = I^2 \times R \times t$.

Power ($P$)

The rate of doing work or using energy, measured in watts ($W$). Formulas include $P = V \times I$ and $P = I^2 \times R$.

Resistivity ($\rho$)

The resisting power of a specified material, used in the formula $R = \frac{\rho \times \ell}{A}$.

Temperature Coefficient of Resistance ($\alpha$)

The increase in unit resistance of a substance per unit rise in temperature from $0\,^\circ\text{C}$, defined by the formula $R_t = R_0 \times (1 + \alpha \times t)$.

Internal Resistance ($r$)

The resistance within a cell that causes an internal volt drop when current is flowing, resulting in a lower terminal voltage ($V = E - I \times r$).

Magnetic Flux ($\Phi$)

The entire quantity of magnetic lines surrounding a magnet, measured in webers.

Flux Density ($B$)

The number of magnetic lines of force per unit area, measured in tesla ($T$).

Fleming's Left-Hand Rule

A rule for motor action where the index finger is flux, the middle finger is current, and the thumb indicates the direction of force.

Transformer

A device consisting of primary and secondary windings used to step voltage up or down via mutual induction.

Auto-transformer

A transformer in which the primary and secondary windings are connected electrically as well as magnetically, sharing a portion of the same winding.

Fleming's Right-Hand Rule

A rule for generator action where the index finger is flux, the thumb is motion, and the middle finger indicates the induced emf.

Frequency

The number of cycles an alternating current wave completes in one second, measured in hertz ($Hz$). In South Africa, the standard is $50\,Hz$.

Primary Cell

An electric cell in which the chemical-to-electrical energy conversion is not reversible, such as a Leclanche dry cell.

Secondary Cell

A cell that can be recharged repeatedly by passing a current through it, such as a lead-acid battery.

Hydrometer

An instrument used to measure the relative density or specific gravity of an electrolyte to determine the state of charge.

Commutator

A device in a direct current generator that acts as a mechanical rectifier, reversing connections so the output always has the same polarity.

Moving Iron Meter

A robust instrument that works on both AC and DC supplies but has a non-uniform scale.

Moving Coil Meter

A very accurate instrument with a uniform scale that only works on DC supplies.

Insulation Resistance Tester

Also known as a 'Megger', it generates a $500\,V$ DC voltage to test that an installation's insulation resistance is at least $1.0\,M\Omega$.

Current Transformer (CT)

An instrument transformer used to reduce high alternating currents to safe, measurable values, typically with a $5\,A$ standard secondary.

Annealed Copper

Copper treated with heat to make it softer, more flexible, and more conductive, though it reduces tensile strength.

Hard-drawn Copper

Copper with high tensile strength and rigidity, often used for overhead conductors or busbars.

Steel-Cored Stranded Aluminium

A lightweight conductor reinforced with a steel core for high tensile strength, most commonly used for overhead transmission lines.

Mica

An excellent insulator capable of withstanding very high temperatures, used between commutator segments and in heating elements.

PILCSWA

Paper-insulated, lead-covered, steel-wire armoured cable.

Wireway

An enclosed casing such as conduit, sleeving, or trunking used to contain and protect conductors or cables.

Stove Coupler

An approved device used to connect a free-standing cooking appliance rated above $16\,A$.

Simmerstat

An energy regulator switch that controls the average temperature of a stove plate using a heating element and a bimetal strip.

Oven Thermostat Switch

A remote reading device with a bulb containing volatile liquid that controls oven heating elements by sensing temperature through expansion bellows.

Earth Leakage Unit

A device designed to detect an earth fault current and automatically disconnect the supply when it exceeds a value like $30\,mA$.

Core-Balance Earth-Leakage Relay

A protective device that uses a current transformer to monitor the phasor sum of live and neutral currents, tripping if an imbalance occurs.

Lightning Arrestor

A device connected between a busbar and earth to divert transient voltage surges caused by lightning.

Ripple Relay

A load control relay activated by a high-frequency signal from a municipality to switch off non-essential loads like geysers during peak periods.

Doping

The process of adding impurities (N-type like arsenic or P-type like indium) to semiconductor materials to change their electrical characteristics.

Zener Diode

A highly doped silicon diode designed to operate in the reverse bias 'breakdown' region to serve as a voltage reference or stabiliser.

Capacitance

The capacity of a capacitor to store energy, measured in farads ($F$).