tn-016-2015
DESCRIPTION
Technical codeTRANSCRIPT
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Technical Note - TN 016: 2015
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www.asa.transport.nsw.gov.au
Technical Note - TN 016: 2015 Issued date: 13 April 2015
Effective date: 13 April 2015
Subject: Overbridges and footbridges Earthing and bonding requirements
1. PurposeThis technical note is issued by the Asset Standards Authority (ASA) to set out earthing and
bonding requirements for overbridges and footbridges. These requirements support those
contained in T HR CI 12030 ST Overbridges and Footbridges.
The requirements of this technical note will be incorporated into future ASA earthing and
bonding standards.
1.1 Scope This technical note sets out earthing and bonding requirements for bridges located above
railway tracks on the RailCorp network.
This technical note shall be read in conjunction with T HR CL 12030 ST.
The requirements of this technical note are not applicable to temporary scaffolds, barriers and
platforms erected on the bridge for construction purposes.
This technical note is not applicable to air space developments and tunnels. Refer to ESC 370
Air Space Developments and ESC 340 Tunnels for the definition of air space developments and
tunnels respectively.
1.2 Application The requirements of this technical note shall apply to all new overbridges and footbridges, as
well as modification to existing overbridges and footbridges, from the effective date of this
technical note.
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Technical Note - TN 016: 2015
2. Situations where an earthing and bonding design is not required An earthing and bonding design is not required for an overbridge or footbridge if all of the
following conditions are satisfied:
overhead wiring is not attached to the bridge
horizontal safety screens are not attached to the bridge
low voltage equipment, such as lighting, is not on the bridge
high voltage bare aerial conductors are not located above the bridge
Where the above conditions are not satisfied, an earthing and bonding design shall be
undertaken to meet the requirements set out in Section 3 and Section 4 of this technical note.
3. Design for overbridges within the electrified area The electrified area is the area within the RailCorp network for which 1500 V dc overhead wiring
is installed. See T HR EL 00001 ST RailCorp Electrical System General Description for the
geographical limits of the RailCorp electrical system.
Within the electrified area, earthing and bonding arrangements at overbridges and footbridges
shall satisfy the requirements as detailed in Section 3.1 and Section 3.2 of this technical note.
3.1 Design strategy Earthing and bonding issues shall be designed out by separation and isolation of conductive
parts so far as reasonably practicable. Where it is not reasonably practicable to do so, the
design shall achieve an optimum balance of the risks associated with step and touch voltages
and the effects from dc stray currents. If there is a conflict of requirements, the requirements for
controlling electrical safety risks shall have precedence over those for controlling corrosion from
electrolysis.
Where there is a reasonable likelihood that exposed metallic components may be live at 1500 V
under fault conditions, and that there is a risk of electric shock to persons under such
conditions, a suitable conducting path shall be provided for the 1500 V fault current so that the
relevant electrical protection (DCCBs) will operate to clear the fault.
3.2 Design requirements Earthing and bonding design for overbridges and footbridges located within the electrified area
shall comply with the requirements set out in the following sections of this technical note.
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Technical Note - TN 016: 2015 3.2.1 Common requirements
The design of overbridges and footbridges located within the electrified area shall comply with
the following requirements:
the bridge structure shall be insulated from boundary fences, preferably via insulation
panels, as well as other metallic structures and services outside of the rail corridor. See
drawing CV 0478385 for a compliant insulation panel arrangement.
exposed continuous metallic services, such as galvanised steel troughing, crossing the
bridge shall be provided with insulation breaks at a distance of 2 m +/- 0.5 m from the edge
of the bridge or any metallic item attached to the bridge
exposed metallic services that are attached to, and run along the bridge, shall have
insulation breaks at the railway corridor boundary
where possible, all insulation breaks shall be aligned. All insulation breaks shall be clearly
shown on as-built drawings with appropriate labels identifying the isolation gaps.
where a high voltage bare aerial conductor is located above the bridge
o the bridge structure shall not be galvanically connected to an adjacent building. Refer to EP 10 01 00 06 SP HV Aerial Standards for Design and Construction for buildings
that are prohibited to be under high voltage aerial lines.
o suitable measures shall be provided at the entrance to the bridge and at any joints in the bridge structure or other metallic components to mitigate the risk of electric shock
from step and touch voltages due to fallen conductors
buildings on the bridge shall not be located under the high voltage aerial line. Refer to
EP 10 01 00 06 SP for prohibited configurations with buildings under high voltage aerial
lines.
test terminals shall be provided to allow for testing of the integrity of the installation,
including the effectiveness of insulation across any joints and the continuity of bonding
circuits, during commissioning and maintenance
where low voltage equipment, such as lighting, is installed on the bridge, earthing
arrangements shall comply with EP 12 10 00 21SP Low Voltage Installations Earthing
design of the bonding circuit shall minimise the inserted impedance and shall ensure that
the relevant DCCB will operate under fault conditions
3.2.2 Concrete bridges The design of concrete overbridges and footbridges located within the electrified area shall
comply with the following requirements.
horizontal safety screens shall be insulated from the bridge structure by ASA type
approved means
vertical safety screens shall be insulated from the bridge structure
other conductive parts, such as protection screens and balustrades, shall be insulated from
the bridge structure
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Technical Note - TN 016: 2015
where overhead wiring structures, such as drop verticals and anchor brackets, are
attached to the bridge, such structures shall be insulated from the bridge by ASA type
approved means
horizontal safety screens and overhead wiring structures attached to the bridge shall be
bonded to rail via an ASA type approved voltage limiting device. See T HR EL 08001 ST
Safety Screens and Barriers for 1500 V OHW Equipment for bonding requirements of
horizontal safety screens, and associated minimum insulation resistance requirements.
See EP 12 00 00 02 SP Low Voltage Distribution and Installations Earthing References
and Definitions for requirements of the bonding conductor.
Currently, ASA type approved means of attachment that satisfy the above insulation
requirements include the use of Hilti HIT-Bar and Sustarin C acetal copolymer (black) in
arrangements detailed in TMC 331 Design of Overhead Wiring Structures and Signal Gantries.
Where the effects of dc stray current have been assessed as critical at the bridge, ASA type
approved supplementary insulation shall be provided in one of the following arrangements:
Preferred arrangement - Supplementary insulation is provided between the overhead
wiring structure and the bridge structure, and between the basic insulation and the
overhead wiring structure. Bonding of the overhead wiring structures or fittings is not
required under this arrangement. See drawing EL 0523806 for a typical installation with this
arrangement.
Alternate arrangement Supplementary insulation is provided between the basic insulation
and the overhead wiring structure. All metallic components of overhead wiring fittings
between the basic and supplementary insulation shall be bonded together and connected
to rail via an ASA type approved voltage limiting device. The voltage limiting device, as well
as joints in the bonding cable, shall be insulated from the bridge structure. See drawing
EL 0282964 for a typical installation with this arrangement.
Refer to AS/NZS 3000 for the definition of basic and supplementary insulation.
3.2.3 Steel bridges The design of steel overbridges and footbridges located within the electrified area shall comply
with the following requirements.
the bridge structure shall be suitable for the 1500 V dc fault current at the location
all metalworks on the bridge, including overhead wiring structures and horizontal safety
screens, shall be galvanically connected to the bridge
the bridge structure shall be bonded to rail via an ASA type approved voltage limiting
device
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Technical Note - TN 016: 2015 3.2.4 Bridges constructed from non-conductive materials
The design of overbridges and footbridges that are constructed from non-conductive materials,
such as brickwork, and located within the electrified area shall comply with the following
requirements:
horizontal safety screens and overhead wiring structures attached to the bridge shall be
bonded to rail via an ASA type approved voltage limiting device
horizontal safety screens and overhead wiring structures attached to the bridge shall be
insulated from other conductive parts on the bridge
4. Design for overbridges outside of the electrified area The design of overbridges and footbridges located outside the electrified area shall comply with
the following requirements.
where a high voltage bare aerial conductor is located above the bridge:
o the bridge structure shall not be galvanically connected to an adjacent building o suitable measures shall be provided at the entrance to the bridge and at any joints in
the bridge structure or other metallic components to mitigate the risk of electric shock
from step and touch voltages due to fallen conductors
o buildings on the bridge shall not be located under the high voltage aerial line. Refer to EP 10 01 00 06 SP HV Aerial Standards for Design and Construction for prohibited
configurations with buildings under high voltage aerial lines.
test terminals shall be provided to allow for testing of the integrity of the installation,
including the effectiveness of insulation across any joints, and the continuity of bonding
circuits, during commissioning and maintenance
where low voltage equipment, such as lighting, is installed on the bridge, earthing
arrangements shall comply with EP 12 10 00 21 SP Low Voltage Installations Earthing
Authorisation:
Technical content prepared by
Checked and approved by
Interdisciplinary coordination checked by
Authorised for release
Signature
Name Wilfred Leung Neal Hook John Paff Graham Bradshaw
Position Principal Engineer Overhead Lines and Cables
Lead Engineer Electrical
A/Chief Engineer Rail Principal Manager, Network Standards and Services
State of NSW through Transport for NSW Page 5 of 5
Technical Note - TN 016: 2015Issued date: 14 April 2015Effective date: 14 April 2015Subject: Overbridges and footbridges Earthing and bonding requirements
1. Purpose1.1 Scope1.2 Application
2. Situations where an earthing and bonding design is not required3. Design for overbridges within the electrified area3.1 Design strategy3.2 Design requirements3.2.1 Common requirements3.2.2 Concrete bridges3.2.3 Steel bridges3.2.4 Bridges constructed from non-conductive materials
4. Design for overbridges outside of the electrified areaAuthorisation: