BBSE2001 – Utility
y Services
http://www.hku.hk/bse/bbse2001/
L.V. Electrical Installation
- Testing Procedures and Extra Low Voltage
Systems
Dr. Sam C M Hui
Department of Mechanical Engineering
The University of Hong Kong
E-mail:
E
mail: cmhui@hku.hk
cmhui@hku hk
Mar 2009
Contents
• Basic Requirements
• Testing Procedures
• Extra Low Voltage (ELV)
• Typical ELV Systems
Basic Requirements
• COP for the Electricity (Wiring) Regulations
• 19: First inspection, testing and certification
• 20: Periodic inspection, testing and certification
• 21: Procedures for inspection,
inspection testing and
certification
• Useful guides:
• EMSD’s
EMSD s Checklists on Items for Inspection and
Testing of Low-voltage Electrical Installations
• HEC’s Guide
id to Connection
i off Supply,
l Chp
h 6&7
Basic Requirements
• First inspection, testing and certification
• For new work, alternation or addition
• Certified by a Registered Electrical Worker (REW)
• Completion
p
of an installation
• Certification on the design
• Certification on the installation
• Work completion certificate
• Before it is energised
Basic Requirements
• Periodic inspection, testing and certification
• Fixed installation requiring annual inspection
• Place of public entertainment
• Premises for manufacturing/storing of dangerous goods
• High voltage installations
• Fixed installation requiring inspection every 5 yrs.
yrs
• Factories & industrial undertakings > 200 A
• Any premises > 100 A
• Hotels, hospitals, schools/universities, etc.
Basic Requirements
• Periodic test certificates
• Form WR2 – a complete installation
• Form WR2(A) – Part of an Installation
• Work Completion Certificates
• Form WR1 – a complete installation
• Form WR1(A) – Part of an Installation
Testing Procedures
• Inspection of L.V.
L V installations, e.g.
eg
•
•
•
•
•
•
•
•
Adequacy of working space & access
Connection & sizes of conductors
Fire protection
Protection against electric shock
Isolation & switching
Overcurrent protective devices
Warning notices and labels
Diagrams, instructions & other info.
Testing Procedures
• Testingg procedures
p
(in
( correct sequence)
q
)
• Continuity of ring final circuit conductors
• Continuity
C ti it off protective
t ti conductors,
d t
including
i l di
main and supplementary equipotential bonding
• Earth electrode resistance
• Insulation resistance
• Polarity
• Earth fault loop impedance
• Functions of all protective devices
• Functions of all items of equipment
Continuity test of final circuit
(Source: EMSD, 2003. Code of Practice for the Electricity (Wiring) Regulations)
Continuity Testers
Digital Multimeter
Earth electrode resistance test
(Source: EMSD, 2003. Code of Practice for the Electricity (Wiring) Regulations)
Test of earth electrode resistance having four or more electrodes
(Source: EMSD, 2003. Code of Practice for the Electricity (Wiring) Regulations)
Insulation resistance to earth test
(Source: EMSD, 2003. Code of Practice for the Electricity (Wiring) Regulations)
Minimum values of insulation resistance
Circuit nominal
g (Volts)
(
)
voltage
Test voltage d.c.
((Volts))
Extra-low voltage *
250
Minimum
insulation
resistance
(megaohms)
0.25
Up to 500 V
500
05
0.5
Above 500 V
1,000
1.0
* When the circuit is supplied from a safety isolating transformer
or safety extra-low voltage (SELV).
(Source: EMSD, 2003. Code of Practice for the Electricity (Wiring) Regulations)
Insulation Tester (MegOhmMeter)
Earth Bonding
Resistance Meter
Insulation resistance test between phases
(Source: EMSD, 2003. Code of Practice for the Electricity (Wiring) Regulations)
Polarity test
(Source: EMSD, 2003. Code of Practice for the Electricity (Wiring) Regulations)
Testing Procedures
• Earth fault loop impedance
• Measured by a phase-earth loop tester
• Functions of all protective devices
• Checked by residual current device tester (built-in)
(built in)
• Checked by hand operation (MCB, MCCB, ACB)
• Additional checks for hazardous environment
• Such
S h as DG stores & iindustrial
d i l process
Extra Low Voltage (ELV)
• Extra low voltage (ELV): (弱 電)
• < 50 volts AC or < 120 volts DC
• Low voltage: < 1000 V AC or 1500 V DC
• High voltage: anything exceeding low voltage
• Intrinsically safe circuits (BS 1259)
• Three
Th types off ELV sources:
• Safety extra low voltage (SELV)
• Protective extra low voltage (PELV)
• Functional extra low voltage (FELV)
Extra Low Voltage (ELV)
• Safetyy extra low voltage
g ((SELV)) must be
• Safely separated from other circuits that carry higher
voltages
• Isolated from earth (ground) and from the protective earth
conductors of other circuits
• The safety of an SELV circuit is provided by
• The extra low voltage
• Low risk of accidental contact with a higher
g
voltage
g
• Lack of a return path through earth (ground) that a current
could
cou
d ta
takee in case oof co
contact
tact with
w t a human
u a body
Extra Low Voltage (ELV)
• Protective extra low voltage
g ((PELV))
• Has a protective earth (ground) connection
• Such as a computer with a IEC Class I power supply
• Functional extra low voltage (FELV)
• Any other extra low voltage circuit that does not fulfill the
requirements for an SELV or PELV circuit
• Such as part of the circuit uses an ELV
• Protection requirements
q
for the higher
g
voltage
g have to be applied
pp
to the entire circuit
Typical ELV Systems
• Common ELV systems include:
• Communal aerial broadcast distribution (CABD)
• Also known as “Public TV antenna” (公共天線)
•
•
•
•
•
Satellite master antenna television (SMATV)
(
)
Private branch exchange (PBX) telephone systems
Public address (PA) systems
Computer networking systems
Fire alarms and security systems
Typical ELV Systems
• CABD and SMATV systems
• Known as “In-Building Coaxial Cable Distribution
S
Systems”
” (IBCCDS)
• Comprises aerial, head-end equipment (amplifier/filter)
and co-axial cable network (block wiring systems)
inside multi-storey buildings
• For reception and distribution of TV and FM radio
broadcast
• In some buildings, it is also used to distribute cable TV,
satellite TV,, closed circuit television ((CCTV)) &
Internet services
(Source: HKU Telecomm Research Project, www.trp.hku.hk)
Typical ELV Systems
• CABD and SMATV systems (cont
(cont’d)
d)
• Services include:
•
•
•
•
Free TV Programme (TVB & ATV)
Satellite TV
Pay TV (CableTV, PCCW Media & TVB Pay Vision)
Digital Terrestrial Television (DTT) (from 2007)
• SMATV: receiver dishes on rooftops and signals
are fed
f d down
d
through
h
h IBCCDS
• Set-topp boxes (機頂盒) : access function &
security function
Typical ELV Systems
• Digital TV
• Broadcast TV services in digital format
• Clear picture & no ghosting
• Supports
pp
more free-to-air TV channels,, high
g
definition TV (HDTV) & interactive TV
• Support
S
t mobile
bil / portable
t bl reception
ti
• How to receive it?
• External decoder added between TV socket and
conventional TV set
• Integrated digital TV set with decoder built in
Comparison of analogue & digital TVs
Analogue TV
(standard definition)
Digital TV
(high definition)
Resolution up to 575 lines
(vertical) x 720 pixels (horizontal)
Resolution up to 1080 lines
(vertical) x 1920 pixels
(horizontal)
Aspect ratio 4:3
Aspect ratio 16:9 (Widescreen)
Stereo sound
Multi sound channels (e.g. Dolby
5.1 multi
multi-channel
channel sound)
(Source: Office of Telecomm Authority, www.ofta.gov.hk)
Timetable for Digital Terrestrial Television (DTT) implementation in
Hong Kong
(* Si
Simulcast
l
= simultaneous
i l
analogue
l
& digital
di i l broadcasts)
b d
)
(Source: www.digitaltv.gov.hk)
Typical ELV Systems
• Digital
g
TV pplatforms in Hong
g Kong
g
• Terrestrial radiocommunications
• Through Ultra High Frequency (UHF) radio spectrum
• By TVB and ATV (launched in Dec 2007)
• Cable
C bl (e.g.
(
by
b Cable
C bl TV)
• Via hybrid fibre coaxial cable (HFC) network
• Broadband network
• Byy PCCW Media & TVB Pay
y Vision ((Galaxy)
y)
• Satellite (through SMATV systems)
• Some foreign & local satellite television broadcasts are
providing HDTV programmes
High
g definition TV (HDTV)
(
) equipment
q p
setupp
(Source: Office of Telecomm Authority, www.ofta.gov.hk)
Reception of Digital TV signals through CABD systems
(Source: www.digitaltv.gov.hk)
Dish = satellite dish
LNB = low noise block down converter
(Source: www.asiasat.com.hk)
(Source: www.asiasat.com.hk)
Typical ELV Systems
• Satellite receivable in Hong
g Kongg
•
•
•
•
•
•
•
•
•
Agila 2 (馬布海2號)
Apstar VI (亞太衛星VI)
AsiaSat 2 (亞洲衛星2號)
AsiaSat 3S (亞洲衛星3S)
Palapa C2 (印尼Palapa C2)
PanAmSat 2, 8, 7 / 10 (美國泛美2號, 8號, 7/10號)
Sinosat 1 (鑫諾1號)
Telstar 10 (Apstar IIR) (亞太衛星2R)
Th i
Thaicom
1A,
1A 2,
2 3 (泰國衛星1A,
(泰國衛星1A 2/3號)
Typical ELV Systems
• Private branch exchange (PBX) systems
• Also, private automatic branch exchange (PABX)
• A telephone exchange that is owned by a private
business,, to allow all users to share a certain
number of external phone lines
• Main purpose: to save the cost of requiring a line for
each user
• Old PBXs
PBX use analog
l ttechnology
h l
g
technology
gy
• New PBXs use digital
Typical ELV Systems
• A PBX includes:
• Telephone trunk (multiple phone) lines that terminate at
the PBX
• A computer
t with
ith memory th
thatt manages the
th switching
it hi off
the calls within the PBX and in and out of it
• The network of lines within the PBX
• Usually a console or switchboard for a human operator
• Larger manufacturers of PBXs:
• Lucent Technologies, NORTEL, Rolm/Siemens, NEC,
GTE, Intecom, Fujitsu, Hitachi, and Mitel
• Latest trends: “IPBX” uses Internet Protocol to carry
ca s
calls
Typical ELV Systems
• PBX p
performs three main duties
• Establish connections (circuits) between the
telephone sets of two users (e.g.
(e g mapping a dialled
number to a physical phone, ensuring the phone
isn'tt already busy)
isn
• Maintain such connections as long as the users
require
i them.
th
(i.e.
(i channeling
h
li voice
i signals
i l
between the users)
• Provide info for accounting purposes
• Other functions,
functions e.g.
e g call transfer
Typical ELV Systems
• Public address (PA) systems
• Also known as “Tannoy”
• An electronic amplification system used as a
y
in public
p
areas
communication system
• Amplifier, loud speaker & mixer for sound control
• Can be fixed or portable,
portable indoor or outdoor
• For general announcement, background music or
emergency messages
• Details of equipment are determined by discussion
with the manufacturers
Examples of public address (PA) systems