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NQF4 - Electrician > KM05 > Flashcards

KM05 Flashcards

Wireways and Wiring Techniques (62 cards)

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1
Q

What is the Principles of Earthing an Bonding

A

Earthing networks are designed to fulfil a number of functions. They can be independent or operate together to provide one or more of the following:
* Safety of persons with respect to electrical hazards.
* Protection of equipment with respect to electrical hazards.
* A reference value for reliable, high-quality signals.
* Satisfactory EMC performance.

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2
Q

What is Earthing

A
  • Earthing is a safety measure designed to prevent electric shock.
  • Earthing conductor will direct any earth fault currents to the ground.
  • Earthing is done to exposed conductive parts that are part of the installation.
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3
Q

What is Bonding

A
  • Bonding is a safety measure designed to reduce electric shock.
  • Bonding conductor will direct any earth fault current to the ground.
  • When we refer to bonding we refer to all exposed conductive parts that do not form part of the electrical installation are brought to the same potential.
  • This is done by connecting all the exposed conductive parts by use of bonding conductor and then connected to the main earth terminal.
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4
Q

Electricity Supply Systems
Code First Letter
I

A

I all live parts are isolated from earth or one point is connected to earth through impedance.

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5
Q

Electricity Supply Systems
Code Firts Letter
T

A

T one or more parts are connected direct to earth;

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6
Q

Electricity Supply Systems
Code Second letter
T

A

T the exposed conductive parts of the consumer’s electrical installation are connected direct to earth, independently of the earthing of any point of the source of energy

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7
Q

Electricity Supply Systems
Code Second Letter
N

A

N the exposed conductive parts of the consumer’s electrical installation are connected direct to earth, independently of the earthing of any point of the source of energy

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8
Q

Electricity Supply Systems
Code - First Letter?

A

The first letter of the identification code denotes the relationship of the source of energy to earth

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8
Q

Electricity Supply Systems
Code subdivided
C

A

C- the neutral and protective functions on the incoming supply and in the consumer’s electrical installation are combined in a single conductor.

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9
Q

Electricity Supply Systems
Code Subdivided
S

A

S- the neutral and protective functions on the incoming supply and in the consumer’s electrical installation are provided by separate conductors.

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10
Q

Electricity Supply Systems
Code - Second Letter?

A

The second letter of the identification code denotes the relationship of the exposed conductive parts of the consumer’s installation to earth

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11
Q

Electricity Supply Systems
Code Subdivided
C-S

A

C-S- the neutral and protective functions on the incoming supply are combined in a single conductor and in the consumer’s electrical installation are serviced by separate conductors.

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12
Q

Electricity Supply Systems
Code - Futher Subdivided Letter?

A

The designation TN is further subdivided depending on the arrangement of the neutral and protective conductors. A further letter or letters denotes such arrangement, as follows

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13
Q

What Earthing System is this?

A

TN-C-S System Earthing

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14
Q

What Earthing System is this?

A

TN-S System Earthing:

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15
Q

What Earthing System is this?

A

TT System Earthing

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16
Q

What Earthing System is this?

A

IT System Earthing

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17
Q

What Earthing System is this?

A

TN-C System Earthing

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18
Q

Name 5 Methods of Earthing

A
  1. Plate Earthing
  2. Pipe Earthing
  3. Rod Earthing
  4. Strip or Wire Earthing
  5. Earthing through waterman (galvanized GI)
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19
Q

Name 5 Types of Bonding

A
  1. Main Bonding
  2. Supplementary Bonding
  3. Equipotential Bonding
  4. Exponential Bonding
  5. Aircraft Electrical Bonding
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20
Q

Earthing and Bonding on low voltage overheard lines

What Equipment is needed

A
  1. Short-circuit and earth fault indicators.
  2. Short-circuit indicators.
  3. Short-circuit and earth fault indicators.
  4. Directional short-circuit and directional earth fault indicators.
  5. Earth fault indicators
  6. Short-circuit indicators for overhead lines
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21
Q

Earthing and Bonding on low voltage overheard lines

What Voltage Detectors and Voltage Detecting Systems is needed

A
  • Voltage detectors
  • Voltage detecting and voltage indicating systems
  • Phase comperators
  • Accessories
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22
Q

Earthing and Bonding on low voltage overheard lines

Earthing Devices and Accessories Needed

A
  • Earthing and short-circuiting devices
  • Connection points
  • Line clampsInsulating stick
  • Accessories
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23
Q

Regulatory and Statutory Requirements related to Earthing and Bonding

A

The employer must take reasonable measures to ensure that no person suffers any electrical shock, thermal burning or electrocution as a result of:
* Exposure to current flow.
* A Person unintentionally coming into contact with exposed parts of any electrical apparatus; exposure to thermal effect, overcurrent, short circuit, fault current, earth fault, overvoltage and Undervoltage.
* Any electrical apparatus failing due to electromagnetic interference from other equipment.
* Any electrical apparatus being incorrectly selected, installed, operated or maintained.
* Any electrical apparatus being placed and protected in such a manner as to allow inadvertent contact with any live portion thereof.
* Any exposure to fires as a result of electrical faults.

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24
What is the Requirements for earthing Arrangments?
The requirements for earthing arrangements are intended to provide a connection to earth that * is reliable and suitable for the protective and functional requirements of the installation (for example, surge protection devices, etc.), * can carry earth fault currents, protective conductor currents and leakage currents to earth without danger from thermal, thermomechanical and electromechanical stresses and from electric shock that arise from these currents, and * where relevant, is also suitable for functional requirements.
25
What is the requierments for an Earth Continuity Conductor?
An earth continuity conductor shall: * consist of compatible conductors, * if it forms part of a cable other than a flexible cable, comply with the relevant requirements of the standard for the cable, * if it forms part of a flexible cable, be of the same material as, and have a nominal cross-sectional area at least equal to, that of the largest phase conductor, * be able to carry the prospective fault current without excessive temperature rise of the conductor, within the disconnecting time * if it does not form part of a cable or flexible cable, have a nominal cros- sectional area at least equal to that determined in accordance with table 6.28(a)
26
What Exposed conductive parts needs to be Earthed
The following conductive parts shall be earthed: 1. all exposed conductive parts of an installation other than those described in 6.12.3.2; NOTE Metal enclosures on PVC conduit should be earthed if they can become live and can be touched. 2. all conductive cable sheaths and armouring, wireways and catenary wires; 3. the earthing terminal of a socket-outlet; 4. the secondary winding of a transformer if it is not a safety transformer; 5. earthing terminals of all permanently connected electrical equipment and appliances; 6. conductive parts of discharge luminaires and equipment that need special earthing arrangements; and 7. all class I equipment.
27
What conductive parts **do not need** to be earthed:
1. short unexposed lengths of metallic wireway used to protect wiring as it passes through a building element 2. exposed conductive parts of fixed electrical equipment that are – out of arm's reach from the floor (or walking) level, – out of arm's reach from a structure that is bonded to earth, and – not exposed to the weather or to the condensation, dripping, splashing or accumulation of water, and– not touching a conductive surface 4. conductive parts that cannot be touched by the standard test finger 5. fixings such as cleats, clips, saddles and clamps 6. equipment and appliances permanently connected to safety supplies 7. small parts such as screws or nameplates that are isolated by insulating material 8. structural steelwork, including items such as fire escapes and cat ladders 9. metallic fittings in bathrooms if they are isolated from earth
28
# Regulatory and Statutory Requirements related to Bonding What is the aim of Bonding
The aim of bonding is to bring all the bonded parts to the same electrical potential.
29
# Regulatory and Statutory Requirements related to Bonding When is an external conductor not required
No external conductor is required if compliance with the requirements for continuity can be proved by the test in 8.6.2.(Continuity of Bonding)
30
# Regulatory and Statutory Requirements related to Bonding A Bonding conductor shall...?
A bonding conductor shall * have a nominal cross-sectional area of at least 2,5 mm2 copper or equivalent, and * be so arranged that it cannot be tampered with.
31
# Regulatory and Statutory Requirements related to Bonding What Parts need to be bonded?
* Hot and cold water systems * Antennas * Roofs, gutters, down pipes and waste pipes * Water pumps * Other Services: – Telecommunications lines – Water services – Gas services
32
What is the aim of SANS 10142-1
To ensure that people, animals and property are protected from hazards that can arise from the operation of an electrical installation under both normal and fault conditions. An electrical installation has to provide protection against: 1. shock current 2. overcurrent 3. fault current 4. overvoltage 5. undervoltage 6. excessive temperatures 7. electric arcs.
33
# Regulations and Statutory Requirements for wiring premises The type of wiring and methods of installation shall be determined after consideration of what?
1. The location (also consider intentional or inadvertent damage) 2. The nature of the building elements for supporting the wiring 3. The accessibility of the wiring to persons and livestock 4. The voltage 5. The electromechanical stresses and thermal effects likely to occur as a result of short-circuits 6. Stresses imposed on the wiring during installation and in service.
34
# Regulations and Statutory Requirements for wiring premises What is the regulation regarding Disconnecting Devices for Equipment
An appliance or equipment that is not supplied from a socket outlet, including equipment automatically or remote controlled, shall be capable of being disconnected from the supply by an easily accessible switch-disconnector. The disconnector shall be mounted (if not specified elsewhere in SANS 10142) *** Within arms reach from the terminals of the appliance, or * In a distribution board, if the device is capable of being locked in the open position.**
35
# Regulations and Statutory Requirements for wiring premises What is the reluation regarding Disconnecting of Neutral Conductors
* A neutral conductor shall not have a single-pole disconnecting device. * In the case of a single-phase circuit, the disconnecting device shall disconnect live and neutral. * In the case of a multiphase circuit, the disconnecting device shall disconnect all the phase conductors but need not disconnect the neutral conductor in an installation connected to a supply system in which the neutral conductor is earthed direct (TN system).
36
# Regulations and Statutory Requirements for wiring premises Distribution Boards
Each distribution board shall be controlled by a switch-disconnector. The switch-disconnector shall * Be mounted in the distribution board or adjacent to the distribution board in the same room – In the case of the main or first distribution board of an installation, be labelled as “main switch” – In the case of a sub-distribution board, be labelled as ‘’sub-main switch” or “main switch” if the board is labelled “subboard” – In the case where an alternative supply is installed (emergency supply, uninterruptible power systems (UPS), etc.), be labelled at the main switch, and– Have a danger notice on or near it. The danger notice shall give instructions that the switch-disconnector be switched off in the event of inadvertent contact or leakage.
37
What is the MInum and Maximum Height for a Distribution Board
1.2M 2.2M
38
# Regulations and Statutory Requirements for wiring premises Switch-disconnector | Cooking Appliance
A switch disconnector for a cooking appliance shall * Be in the same room as the appliance * Be at a height above floor level of not less than 0,5 m and not more than 2,2 m * Preferably not be above the cooking appliance * Be within 3 m of the appliance, but within 0,5 m of the appliance if the switch-disconnector’s purpose is not clearly indicated * Not be fixed to the appliance
39
# Regulations and Statutory Requirements for wiring premises What is the Requierments for Water Heaters
* All water heaters shall be bonded in and a.c. supply circuits shall be protected by earth leakage protection with IΔn not exceeding 30 mA. * NOTE To mitigate nuisance earth leakage tripping, an additional earth leakage may be provided. * * Dedicated circuits shall be provided for water heaters and there may be more than one water heater on each circuit.
40
# Regulations and Statutory Requirements for wiring premises What is the requierments for Fixed Appliances
* The power supply to every fixed appliance, except luminaires, shall be supplied through:– a disconnecting device that disconnects both live conductors and in a single-phase supply and all phase conductors in a multiphase supply, or– a socket outlet * The disconnecting device shall be positioned:– Within 1,5 m from the appliance, or– In a distribution board (if the switch-disconnector is capable of being locked in the open position.
41
Name 7 Types of Wireways
1. Rigid PVC conduit 2. Rigid steel conduit 3. Flexible conduit 4. Trunking 5. Cable Tray 6. Multibore conduit 7. Cable Trench
42
Name the Aplications for Rigid PVC conduit
* Domestic/Residentsal Installations * Indoor and Outdoor * Underground
43
What is the Advantages and Disadvantages of Rigid PVC conduit
Advantages * It can be bent and manipulated easily without special tools or equipment. * It does not corrode or rust. * It can be buried in concrete, plaster or under floor screeds. Disadvantages * It cannot be used where temperatures are lower than 15° C or where the temperature is higher than 70° C. * It cannot be used where it is subjected to ultra-violet light or in direct sunlight as this could break down the material overtime. * It cannot resist mechanical damage like metal conduit can.
44
Name the Aplications for Rigid steel conduit
* Commercial Installations * Industrial Installations * Indoor and Outdoor * Underground
45
What is the Advantages and Disadvantages of Flexible conduit
Advantages * It is easy to work with. Disadvantages * It cannot be used over long distances.
46
Name the Aplications for Flexible conduit
* Commercial Installations
47
Name the Aplications for Trunking
* Residential Installations * Commercial Installations * Industrial Installations
48
Name the Aplications for Cable Tray
* Industrial Installations * Light and Heavy duty cabling
49
Name the Aplications for Multibore conduit
Underground installations
50
Name the Aplications for Cable Trench
Underground installations
51
# General provisions for wireways as prescribed in the SANS 10142-1 General provisions when a wireway is installed
* The wireway shall be installed such that safe maintenance is ensured * Joints other than expansion joints shall be at least as rigid as the Wireway itself * Where flammable material is used for its construction, the electrical equipment mounted in or onto the wireway shall be protected by nonflammablematerial * Expansion joints shall protect the wiring at least as well as the rest of the wireway does * All inspection joints and boxes shall be easily accessible, even if they are above ceilings or below floorboards * All boxes and expansion joints that could be splashed with liquid shall have covers that prevent the liquid from entering the wireways * It shall be able to withstand the environmental conditions in which it isinstalled * Any cable, other than a high-voltage cable for a discharge lamp installation, may be installed in the wireway, except in the case of 6.4.1(b) * No part of the wireway shall be flattened, split or damaged * Metal doors, covers or hinged panels shall be separately earthed where any electrical equipment is fitted to such doors, covers or panels * Where it is accessible to the public, protection shall be such that it is not possible to touch any live parts with either the standard jointed test finger or the 2,5 mm diameter 100 mm long rod (see SANS 60529). This protection also applies after opening any door or cover that can be opened without the use of a tool or key * Cable entry points, exit points, and internal surfaces of the wireway shall not be able to damage the insulation of cables installed.
52
Name the 5 types of Wire
1. Triplex 2. Main Feeder Wires 3. Panel Feed Wires 4. Non-Metallic Sheathed Wires 5. Single Strand Wires
53
Name the 7 wire Colours
1. Black 2. Red 3. Blue 4. Yellow 5. White 6. Green/Green & Yellow 7. Bare Copper
54
# Colour Codes Black
Hot Wire switches and outlets
55
# Colour Codes Red
Hot Wire
56
# Colour Codes Blue
57
# Colour Codes Yellow
58
# Colour Codes White
Always Neutral
59
# Colour Codes Green Green & Yellow Bare Copper
Only for Earthing
60
Name the 12 Types of Electrical Cables
1. Non-Metallic Sheathed Cable (NM-B & NM-C Cables) 2. Matallic Sheathed Cable (Armored / BX Cables) 3. Underground Feeder Cable (UF Cables) 4. Multi-Conductor Cable (MC Cables) 5. Coaxial Cable 6. Unshielded Twisted Pair Cable 7. Ribbon Cable 8. Direct-Buried Cable 9. Twin-Lead Cable 10. Twinaxial Cable 11. Paird Cable 12. Twisted Cable
61

NQF4 - Electrician (6 decks)

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