Technical Note - TN 016: 2015
For queries regarding this document standards@transport.nsw.gov.au
www.asa.transport.nsw.gov.au
3
3
This 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.
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.
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.
© State of NSW through Transport for NSW Page 1 of 5

Technical Note - TN 016: 2015
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.
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.
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.
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.
© State of NSW through Transport for NSW Page 2 of 5

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
© State of NSW through Transport for NSW Page 3 of 5

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
© State of NSW through Transport for NSW Page 4 of 5

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
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
Signature
Technical content prepared by
Checked and approved by
Interdisciplinary coordination checked by
Authorised for release
Name Wilfred Leung
Position Principal Engineer
Overhead Lines and
Cables
Neal Hook
Lead Engineer
Electrical
John Paff Graham Bradshaw
A/Chief Engineer Rail Principal Manager,
Network Standards and Services
© State of NSW through Transport for NSW Page 5 of 5