tn-016-2015

Technical Note - TN 016: 2015

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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.

State of NSW through Transport for NSW Page 1 of 5


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.


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



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


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:


bonded to rail via an ASA type approved voltage limiting device


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


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:

tn-016-2015

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