MEBS6019 Extra-Low-Voltage Electrical
Systems in Buildings
Lecture I – Introduction
Dr. Sam K.H. LAM
Tel: 3917-8401
Email: khlam@eee.hku.hk
Department of Electrical and Electronic Engineering
The University of Hong Kong
1
Course outline
• This course aims at providing knowledge and sharing practical
experience on the application of ELV systems for buildings.
• At the end of this course, students who fulfill the requirements of this
course will be able to:
1. Distinguish between ELV and LV electrical installations; and comprehend the
various purposes of ELV installations;
2. Be aware of the benefits and limitations of ELV as energy and as signal systems.
3. Be alert of the potential hazards of electrical installations, yet be able to
prevent those hazards.
4. Be competent in codes of practice relating to ELV installations; and be
proficient in maintaining safety in ELV installations.
5. Understand fundamental principles effecting ELV applications in building
services.
6. Design, utilize and install ELV applications for new and updated roles in modern
buildings.
2
Class schedule
•
•
•
•
Date: Every THURSDAY 7:00pm - 9:30pm
Venue: MW-T7
Lectures
PART 1 Fundamentals:– Categories of ELV Systems;
LV and ELV Power Distribution
• PART 2 Communication Systems:– Communication
Principles and Networks
• PART 3 Applications:– Practical applications of ELV
systems
3
Course schedule
Course Content
Date
Part 1: Fundamentals
7th Sept., 2023
14th Sept., 2023
21st Sept., 2023
Introduction
Categories of ELV Systems
LV and ELV Power Distribution
Part 2: Communication Systems
28th Sept., 2023
5th Oct., 2023
Communication Principles
Communication Networks
Part 3: Applications
Access Control
Surveillance Systems
Public Address Systems
Lighting Control Systems
Television Systems
Group presentation
Revisions
12th Oct., 2023
26th Oct., 2023
2nd Nov., 2023
9th Nov., 2023
16th Nov., 2023
23rd Nov., 2023
30th Nov., 2023
4
Allocation of marks
• Examination will account for 70% of the overall
marks; 30% will be by coursework – a group
project.
• In the exam, equal split (50-50) of marks on the
contents:
I.
Part 1&2: the course contents for Fundamentals
and Communication Systems;
II. Part 3: the course contents for Practical
applications of ELV systems.
5
In-course assessment
• The in-course assessment will be a group project. Each group shall
have minimum of six students to a maximum of nine students to
submit a report + group presentation.
• Submit the group member list (with student name and UID.) to Dr.
W.Y. Cheung at wycheung@eee.hku.hk on or before 12th Oct.
• Each student shall contribute to the report and participate in the
group presentation.
• You may select one of the following topics or create your own:
i.
ii.
iii.
iv.
ELV DC distribution system;
Advanced surveillance system;
Voice evacuation system;
Smart car-park system.
• Submission deadline: 3rd Dec., 2023. NO late submission will be
marked!
6
Objectives of the assignment
• The assignment is for the students to demonstrate
that they could achieve the following Intended
Learning Outcomes:
– Describe the essential components and design criteria
of a selected ELV system for modern buildings;
– Examine how such system can help improving the
enhance the occupants’ experience inside the
building;
– BONUS level: outline innovative approach(es) to
achieve the intended functions.
7
Merits of electricity as compared with
other forms of Energy
8
Ready to transform
• Transformation in terms of:
–
–
–
–
–
Higher voltage to lower voltage or vice versa
DC to AC or vice versa
Analogue to digital or vice versa
Higher frequency to lower frequency or vice versa
Change of other electrical parameters
• Also it’s readily to be converted into other forms
of energy:
– Mechanical, Sound, Thermal, Radiant, Chemical,
Gravitational, etc.
9
Efficiency in converting to other forms
• Efficiency in converting into other forms of energy
is relatively high:
– Electricity -> Mechanical energy: over 90% by large
motors;
– Electricity -> Light energy: still very effective compare
with other ways (e.g. Kerosene/Gas lamp);
– Electricity -> Thermal energy: over 99% by resistors.
• Hence the overall system efficiency will be higher
by using electricity as energy carrier.
10
Availability
• Ready to get in desirable quantity when
source is abundant:
– Given ease of conversion, hence electricity can be
derived readily and affordably in many “energy
carriers”
– Chemical energy stored in fossil fuels
– Potential energy from river
– Solar energy, etc.
11
Ready to transmit
• It can then be used almost anywhere and not
require transportation of fuel resources over
long distances like coal, oil or gas.
• Transmission effectiveness includes:
–
–
–
–
Quantity & density
Distance
Bandwidth division
Speed of transmission
12
Ready to superimpose or integrate
• By means of:
– Amplification
– Addition
• Particularly useful in communication systems
– Modulation
– Multiplexing
– Power Line Communication (PLC)
13
Ready to be “stored”
• Storage of electricity directly is difficult,
if not impossible. But because of
“ready to convert”; hence we may
convert electrical signal/energy to
other forms of signal/energy capable of
storage.
• Energy storage is one of the most
important operations in modern
systems.
14
Ready to be represented
• Electrical energy or signal can be represented by:
–
–
–
–
–
Mathematics (time-functions)
Graphs and spectrums
Phasors (vectors)
Complex numbers
Hence it rationalize calculation of electrical quantities.
15
Ready to differentiate
• Given ease of computation, hence we may
differentiate various electrical waveforms,
especially when some of the conditions are
well known.
• This means that even when we have
integrated many electrical signals together,
we may still reproduce each of them as their
metrics are known.
16
Analogue and Digital inter-conversion
• For enhancement of Signal Processing & Transmission.
• Given ease of conversion between the two, we may
make use of the advantages of each of them in the subprocesses.
• e.g. Amplifying a sound signal at a distance receiver:
1.
2.
3.
4.
Collect the sound signal
Convert it to electrical analogue
Convert the analogue to digital for transmission efficiency
Restructure it back to analogue, then amplify
17
Ready to represent Data
• Given ease of being represented, the reverse
is also true. Electrical signal may be used to
represent any data you may possibly think
of:
– Waveform, Number, Word, Shape, Colour, Order,
Quality Expression, etc.
– The D/A & A/D power enhances this ability.
18
Ready to maintain, restore and
enhance
• Because of its superimposition nature, we may
restore an electrical signal when it is attenuated or
distorted;
• not to mention that we may indeed amplify or
decorate the signal (e.g. by Fourier transform).
19
Sinusoidal waveforms
• T is period of oscillation
• f = 1/T (frequency)
– Units: Hertz
– cycles per second
•  = 2f = 250 = 314 rads/sec
– angular frequency
– measured in radians per
second
𝑉(𝑡) = 𝑉𝑚 sin( 𝜔𝑡 + ∅)
(1)
•  = phase angle
– offset from zero
20
Effective values of periodic waveforms
• The effective value of a current is
the steady current (dc) that transfers
the same amount of average (real)
power as the given varying current.
• The effective value of a voltage is
the steady voltage (dc) that transfers
the same amount of average (real)
power as the given varying voltage.
Denoted as root mean square (RMS)
value:
Vrms = Vm (cos2 t ) avg = Vm
1 Vm
=
2
2
(2)
21
Fourier Transform for periodic functions
• Fourier Series of a periodic function f(t):
∞
𝑪 𝑡 = 𝑪𝟎 + ෍ 𝑪𝒉 sin( 𝒉𝜔𝑡 + 𝜽𝒉)
𝒉=𝟏
Co =
1
T

T
o
f (t )dt ,
C h = A 2h + B2h
• Applied in electrical systems:
∞
𝑽 𝑡 = 𝑽𝟎 + ෍ 𝑉𝒎𝒉 sin( 𝒉𝜔𝑡 + 𝜽𝒉)
(3)
𝒉=𝟏
∞
𝑰 𝑡 = 𝑰𝟎 + ෍ 𝑰𝒎𝒉 sin( 𝒉𝜔𝑡 + 𝜽𝒉)
(4)
𝒉=𝟏
where h = harmonic order
22
Ready to branch for mass distribution
• Electricity can easily be branched off by proper
arrangement of wires (or other appropriate media).
23
Ready to be distributed via cables
• Good conduction in metal make electricity superb
than any other energy in walking around every part
and every corner of a building or an estate.
• Converting into electricity, and then converting back,
other form of energy may then penetrate better
within a building through the walls and ceilings => it
is therefore the best candidate to carry energy
around in buildings.
24
Other merits
• Make processes easier and less costly;
• Make control and automation easier, and may be
software driven;
• Relatively general environments has smaller
disturbances on an electrical circuit;
• Versatility - use electricity to power a diverse
range of appliances, other energy carriers may not
be as flexible.
25
Details on Conversions
26
Common Electrical Energy metrics
• Primary:
–
–
–
–
Voltage
Current
Power
Energy
• Supplementary:
–
–
–
–
Waveform
Frequency
Power factor
Phase Angle
• Additional:
– Harmonic order, Time division, Wavelength,
Flux, Field strength, etc.
27
Common Electrical Signal metrics
• Analogue
• Metric form with reference values in numbers,
vectors, equations, graphs or tables
• Digital
• Binary form in clusters/combinations of 1/0
bits/bytes to represent analogue metrics and/or
conditions
28
Analogue-to-Digital conversion
• The conversion involves
quantization of the input
periodically. The result is a
sequence of digital values
that have been converted
from a continuous-time and
continuous-amplitude analog
signal to a discrete-time and
discrete-amplitude digital
signal.
Source of image: Petr Adamek
29
Digital representation of waveform
• If we assign:
0 = 0000000
1 = 0000001
2 = 0000010
3 = 0000011, etc.
• Then the waveform can be
represented by:
00000000; 00000100; 00000101;
00000100; 00000011; ……
Source of image: Petr Adamek
30
Digital-to-Analogue conversion
• At the receiver, the digital
values of 0,4,5,4,3……. are
received and interpreted.
• The digital value of 4 will be
treated as 4, and the
receiver cannot detect it as
3.7. Remember this is
quantization error. The
approximation of value over
the time period may also
introduce quantization
error.
31
Digital ramp ADC
Source of image: http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/adc.html
32
Limitations of Electricity
33
Magnetic Influence
• Electricity and Magnetism has mutual-causality
relationship. Presence of one in the vicinity of the
other may affect the latter.
• Hence there will be signal interference
• The disturbance may interrupt, obstruct, or
otherwise degrade or limit the effective
performance of the circuit.
34
Resistance and Impedance
• Resistance causes potential drop (volt drop),
energy loss and signal attenuation. Since resistance
is temperature related, thus the loss and
attenuation effects are also temperature related.
• Impedance is related to the frequency, yet it may
also change the potential and the phase angle.
Source of image:
https://www.engineersedge.com/instrumentation/voltage_drop_calculator/wi
re_voltage_drop_calculator_12928.htm
35
Impedance (Z) and Reactance (X)
Z = V/I
jL
Z = R + jX
X = L
(reactive)
or …
X = -1/C
(capacitive)
-j/C
36
Capacity of transmission
• Good transmission efficiency does not imply perfect
transmission.
• The capacity is limited by material(s), maximum
operating temperature, number of signals,
bandwidth required, joints, dielectric strength, etc.
(on V, I, f)
• If electrical current is carrying information (in
communication circuits), bandwidth of the
communication channel is the major concern.
37
Storage of Electricity
• Few materials and processes
may store electricity
(electrical charges) directly
and practically. The data in
electrical form and the energy
in excess should be converted
for storage.
• There are ALWAYS losses in
the process of conversion ->
energy lost.
Source of image:
https://www.linquip.com/blog/typesof-energy-storage-methods/
38
Hard to perceive
• Bear in mind electricity does not have a
significant physical body.
• It is colourless, tasteless, and odorless. It is
untouchable.
• You may see the effects of electricity, but
not the electricity.
39
Safety concerns
• Electrical circuits and operations must be handled with
alertness and care, for oneself and for others.
• When ELV is provided fully in accordance with
Regulations, the chance of electric shock is ZERO. It is
because the current through the body is too minimal to
influence any organs or tissues.
40
Protection concerns
• The safety concerns and the high density of ready
energy call for essential critical protective
measures.
• Many regulations and rules to observe for safety,
which shall be detailed in the coming lectures.
• Code of Practice for Electricity (Wiring) Regulations
(2020 Edition)
41
Transmission requires a physical medium
• Unless the electrical energy be converted to higher
radiant format, otherwise it must require a “hardwire” medium for transmission (flow of electrons).
• There exist a potential difference (voltage)
between that hard-wire and the “ground”
• To prevent leakage of electric current, we need a
layer of material to cover the hard-wire
42
Leakage of energy and signal
• Due to capacitive effects and possibly insulation
deficiency, energy and signal may leak to the earth or
elsewhere.
• When there is a tee to the circuit, then the tee may
divert energy and signal, thus diminishing the energy and
signal in the circuit.
• Even when there is no tee connection, the coupling
between two circuits may produce electromagnetic
forces on each energy circuits, and cross-talks in signal
circuits.
43
Steady state requires a lead time of transient
44
Vulnerability
• The electrical circuits are
highly vulnerable to
forces of nature, human
disturbances, and
human errors.
• e.g. lightning, magnetic,
snowing, rats, fire, poor
design, etc.
45
Hazards of Electric Shock
46
Voltage or potential-difference
• Voltage is a Electrical Pressure that pushes
electrical energy or its carrier to flow from
the high pressure end to the low pressure
end when there’s a path of good
admittance connecting the two ends.
• The quantity per unit time that flows in the
path is called current.
• Engineers must ensure that both voltage
and current safely performs by the circuit.
47
Safety concerns
• Electricity may injure or kill human beings by:
i. Voltage: causing dielectric breakdown of body;
ii. Current:
– heat burn
– signal distortion resonance
– muscular contraction impairing breathing ventricular
fibrillation.
• Most deaths were results of electrical current, which
will flow through human body when there is a
potential difference established across the body. How
much damage is also dependent on time.
48
Safety concerns (Cont’d)
• Most of the deaths and injuries from Electric Shocks were
not directly due to voltage, but by the current produced
by the voltage.
• The current goes through the limbs and the organs and
produces heat, electromagnetic vibration, compression,
and resonance, etc. All these effects can seriously damage
the organs to non-fully recoverable states.
• Moreover electric currents may inhibit nervous system
instantly, making the victim unable to release himself.
49
How much current can kill you?
https://youtu.be/y_cWTWB-N_I
50
Electrical safety considerations
• For electric current to flow through the body, the body
must become part of an electrical circuit. We therefore
need to understand how currents pass though different
parts of the body and how to limit that flow of current.
• For example, the same person touching an energized
object (at same voltage) may experience differently:
➢ a shock if they were barefoot vs. may not if wearing shoes;
➢ different severity with wet skin vs. dry skin;
➢ different perceptions of the contact modes "foot-to-foot" vs.
"hand-to-foot" vs. "hand-to-hand“.
51
Why ELV?
• In theory, voltage and current are directly proportional. A
smaller voltage gives a smaller current. V = I * Z
• Also, an AC system is more risky than a DC system of same
voltage because the former carrying ripples.
• Relatively, we may say HV is more dangerous than ELV, as
both voltage across body contacts and the current
through body can be higher.
• Hence ELV is used in order to reduce the danger of
electric shock.
52
Electric shock
• Two main types of electric shock:
– Direct contact: when contact is made directly with the live
part which is very likely to cause current flow though the
body.
– Indirect contact: when contact is made with an exposed
conductive part which is not live under normal condition
(but may become live under earth-fault condition).
• Note: overcurrent protective devices and residual
current device RCD may not automatically de-energise
the live parts (e.g. between phase and neutral) when
touched by human => avoid direct contact!!
53
Effects of electrical shock
• Severity of the shock depends
on:
– Path of current through the body.
– Amount of current flowing
through the body.
– Length of time the body is in the
circuit.
• In the most extreme cases, it
could cause death.
54
Damage according to range of currents
• 1 milliamp: Just a faint tingle.
• 5 milliamps: Slight shock felt. Most people can let go.
• 6 - 30 milliamps: Painful shock. Muscular control is lost. This is the
range were “freezing current” starts (> 10mA). It may not be
possible to let go.
• 50 - 150 milliamps: Extremely painful shock, respiratory arrest,
(breathing stops) and severe muscle contractions. Death is possible.
• 1,000 - 4,300 milliamps (1 - 4.3 amps): Arrhythmic heart pumping
action, muscles contract, and nerve damage occurs. Death is likely.
• 10,000+ milliamps (10 amps): Cardiac arrest and severe burns
occur. Death is probable.
55
Human body impedance
• The impedance of the human body can
be broken down into the impedances of
the various body parts, resulting in an
equivalent circuit for the electrical path
through the body.
• Human body impedance is characterized
as that of a bulk medium, which
combines the elements of inductance,
resistance, and capacitance in one solid.
56
Current through human body
• Body resistance varies depending on how contact is made with the skin:
is it from hand-to-hand, hand-to-foot, foot-to-foot, hand-to-elbow, etc.
• Under dry conditions, the resistance offered by the human body may be
as high as 100,000 Ohms. Wet or broken skin may drop the body's
resistance to 1,000 Ohms. (high-voltage breaks down human skin,
reducing the human body's resistance to 500 Ohms).
• Body impedance of a hand-to-hand circuit for dry skin, large contact
areas, 50Hz AC currents:
57
Effects on the human body
• The longer the exposure, the increased danger of shock to
the victim.
• Low voltage can be dangerous because the degree of injury
depends not only on the current, but on the length of time in
contact with the circuit.
• High voltages lead to additional injuries such as violent
muscular contractions. Muscle contractions may cause bone
fractures from either contractions themselves or from falls.
Also can cause internal bleeding, destruction of tissues,
nerves and muscles.
• Skin is also subject to dielectric breakdown at around 200V
AC.
58
Protection against direct contact
• Source of image: G. Stokes (2002), A practical guide to the wiring regulations,
Oxford, http://library.hku.hk/record=b2770076
59
Protection against indirect contact
• To prevent any exposed conductive part
becoming live by reinforced insulation
• Special areas restricted to skilled and instructed
personnel
• Earth-free installations of a special nature
• To provide particular requirements: different
categories of ELV systems
60
Definitions and characteristics of ELV
61
Electricity classification by Voltages
Highest
Voltage
AC between
conductors
EHV
AC to earth
DC between
conductors
DC to earth
No limit
No Limit
No limit
No limit
345kV
275kV
Ultra
Ultra
MV
35kV
20kV
Uncommon
Uncommon
LV
1000V
600V
1500V
900V
50V
50V
120V (ripple-free)
120V (ripple-free)
Small V
Small V
Small V
Small V
HV
ELV
Signal
HV
62
Graphical representation
63
Application of different voltage levels
• At the other extreme, as buildings get taller and larger.
To overcome excessive voltage drops and heat loss, the
MV installation also becomes common.
• But we use MV for main distribution only between/in
the buildings, i.e. there is a main MV distribution panel
at the ground floor or basement, and then placing some
11kV/380V (or 22kV/380V) transformers in some
middle floors to supply electricity to upper part of the
building.
64
Considerations in applying ELV
• We can consider ELV when any one of these 3
conditions apply:
– Small power applications
– Local utilization (short cable length)
– ELV as Signals
• In other words, when we use ELV, we must watch
these conditions. There are 3 types of ELV. Each has
its own requirement besides these listed conditions.
On top, reduced voltage from LV is also permitted.
65
Applications of ELV
• Despite this limits the performance of large power applications by
ELV, nonetheless the information age demands signal operations that
are substantially driven by ELV (AC or DC).
• Examples are computers & peripherals, LED TV, communication
panels, control panels, etc.
• ELV for certain “local” power applications. E.g. LED lightings,
emergency lightings, shaver units, small fans, battery chargers, etc,
when the demand is <100W.
• Communication; computing; control; remote-switching; visual; audio;
testing; electronics equipment; other small power applications; etc.
• Also many renewable sources may be ELV.
• New trend: to use DC distribution in buildings, part of which would
be ELV.
66
Recommended Readings
1. Georgia State University Department of Physics & Astronomy
website: https://physics-astro.gsu.edu/
2. EMSD, Code of Practice for Electricity (Wiring) Regulations
(2020 Edition):
https://www.emsd.gov.hk/filemanager/en/content_443/COP
_E_2020.pdf
3. C. Strauss, Practical Electrical Network Automation and
Communication Systems, Elsevier
http://find.lib.hku.hk/record=alma991018398789703414
67