Electrical Installation Design Flashcards
What key factors must be considered in assessing supply details for an electrical installation design?
Live conductors, current, prospective fault current, and earthing arrangement
In a typical single-phase 230 V supply in the UK, how many live conductors are there?
Two
In the UK, what is the voltage for three-phase supplies without a neutral conductor?
400 V
Why are three-phase supplies preferred for larger installations requiring more than 100 A of power?
They are more energy-efficient.
What does the term “nominal voltage” refer to in electrical installations?
The voltage measured between live and earth in the UK
How does the real voltage in an installation relate to the nominal voltage?
The real voltage is always lower than the nominal voltage.
Which type of conductor arrangement is common in larger retail outlets and larger commercial or industrial buildings in the UK?
Three-phase with a neutral
What is the maximum current rating typically associated with small domestic-type installations in the UK?
100 A
In a three-phase and neutral supply in the UK, what are the voltages for line-to-neutral (L-N) and line-to-line (L-L)?
L-N: 230 V, L-L: 400 V
Which type of conductor arrangement is not very common in the UK due to the requirement for all circuits to be three-phase balanced loads?
Three-phase 400 V
According to UK regulations (BS 7671), where can you find diagrams of various conductor arrangements?
Chapter 31
What does the term “external impedance” refer to in the context of earthing arrangements?
Resistance between the installation and the substation transformer
why is it essential to know the supply details before designing an electrical installation?
To ensure the safety of the installation
In the UK, what is the primary difference between a single-phase 230 V supply and a three-phase 400 V supply?
The number of live conductors
What is the purpose of a neutral conductor in a three-phase and neutral supply (L-N : 400 V L-L) in the UK?
To balance the phases and carry unbalanced current
In an electrical installation located far from the substation transformer, how does the distance impact the real voltage compared to the nominal voltage?
The real voltage is lower as distance increases.
What is the purpose of using nominal (normal) values in electrical calculations?
To account for voltage variations due to demand and distance
Which of the following is NOT a common type of conductor arrangement in the UK?
Four-phase
What is the primary reason for using a three-phase supply for larger installations?
It provides better voltage regulation.
What is the maximum demand typically associated with most average-sized houses in the UK?
Less than 100 A
In larger installations with a maximum demand over 100 A, what is often used to distribute the load in the supply?
Three-phase supply
When a building needs a supply over 400 A per phase, what may be installed on-site to provide the required capacity?
A substation transformer
What factors govern the maximum demand for an electrical installation?
The size of the incoming supply cables
Why is it essential to check the supply capacity when adding to an existing electrical installation?
To prevent overload and ensure safety
hen a new building is to be given an electrical supply, what information does the Distribution Network Operator (DNO) need?
site plans, load requirements, and property details
What is the responsibility of the consumer once the electrical supply has been metered?
To pay the electricity bill and maintain the internal electrical system
In newer buildings, what component is often found between the meter and the consumer unit (CU)?
Isolation switch
What is the most common current rating for house supplies in the UK?
80 A
What term is used to describe the maximum demand in electrical installations?
Maximum demand
If a building needs a supply over 400 A per phase, what infrastructure might be added on-site?
Substation transformer
What governs the maximum demand for an electrical installation?
size of the incoming supply cables and the DNO’s service fuse rating
What kind of information does the Distribution Network Operator (DNO) need when providing a new electrical supply to a building?
Load requirements and property details
What is the primary role of a designer in the context of a new electrical installation?
To provide the DNO with the proposed maximum demand for the installation
In the UK, what is the most common earthing arrangement used in electrical installations?
TN-C-S
How does a Distribution Network Operator (DNO) seal their service fuse and meter connections?
With a small wire and a sealing crimp tool
Why are tails insulated and sheathed in electrical installations?
To improve mechanical protection
What is the primary reason for having two layers of insulating material on tails?
To improve protection and reduce the risk of electric shock
In what location should tails have insulation and sheathing extending up to?
B) The point where they connect to the main switch inside the consumer control unit
What type of cable should be used for tails when the consumer control unit (CU) is located away from the meter point?
Steel-wire armour cable
What determines the cross-sectional area (csa) of tails in an electrical installation?
The intended maximum demand or the stipulation of the DNO
According to Regulation 522.8.5, how should meter tails be supported to avoid undue strain on terminations?
By supporting them with clips or cleats
What are the three common circuit arrangements in electrical installations?
Radial power circuits, ring-final circuits, and radial lighting circuits
What is a major advantage of using radial power circuits?
he cable csa is designed to match the load and protective device
In a ring-final circuit, what happens if a fault occurs, such as a loose connection (open circuit)?
The equipment continues to function
What type of circuit should be used for lighting circuits that primarily use energy-efficient LED lighting?
3 A rated circuits
What is the primary purpose of a ring-final circuit in the UK?
To supply socket outlets with conveniently placed outlets
Which of the following statements about ring-final circuits is true?
Ring-final circuits can supply an unlimited number of outlets in a maximum floor area of 100 m2.
What is a “spur” in the context of electrical circuits?
A branch circuit
Why is it recommended to minimize the use of spurs in electrical circuits?
Too many spurs can make fault detection harder
What are some disadvantages of ring-final circuits?
Overloaded circuit conductors may not be detected.
What rating are lighting circuits generally rated at in the UK?
6 A
In what situations might lighting circuits be wired using the “three-plate” method?
C) When using composite cables
What is the advantage of installing the “three-plate” at a switch instead of at a light point?
It reduces the number of connections at luminaires.
How are additional light points typically added to a lighting circuit wired in the “three-plate” method?
By looping off the ceiling rose
What should be considered when selecting the rating for lighting circuits in installations using energy-efficient LED lighting?
The energy consumption of the LED lights
What is the primary advantage of using the conduit method for wiring?
It allows for direct drawing of cables without breaking at light points.
How can lighting circuits be efficiently controlled for energy conservation?
By arranging automated switching devices.
What does diversity take into account when sizing distribution circuits?
The fact that not all loads will be fully loaded simultaneously.
Final circuits are NOT typically subjected to:
Diversity considerations.
which term is used to describe a circuit used for remote switching or monitoring?
Auxiliary circuit.
What is the primary reason for dividing an electrical installation into circuits?
To minimize danger or inconvenience in case of a fault.
What type of wiring system is suitable for distributing large cables around a building or site?
Cable ladder, cable tray, cable brackets.
What is the purpose of essential circuits in an electrical installation?
To provide power to equipment like IT systems in case of power loss.
Which external influence should be considered when selecting a wiring system?
Ambient temperature.
Which wiring system is commonly adopted in industrial premises where the presence of cables is acceptable?
Clipped direct sheathed with armor.
What is the primary purpose of distribution circuits in electrical installations?
To reduce the length of final circuits.