Issued by Chief Engineers Division
Electrical Technical Note
Minimum Electrical Clearance for
1500V dc Overhead Wiring
ETN 11/04
Version 2
01/11/2012
Expires
01/11/2014
The minimum electrical clearance between live overhead wiring (OHW) parts and
earthed or rail connected structure, and between OHW conductors of different
electrical sections, is 150mm. Infringement of this minimum electrical clearance
may cause serious network incidents, as illustrated in the photograph at the end of
this Technical Note.
The actual clearance to live OHW parts may vary due to changes in conductor
temperatures and tensions, wind conditions, dynamic effects on conductors from
the passage of trains, wire creep, as well as maintenance activities. For example, a
point (such as a dropper attachment) on a conductor of a regulated OHW system
may move by 1m in the along track direction through the design temperature range
(see EP 08 00 00 01 SP section 6.3). In an overlap with moving anchors at both
ends of the overlap, the longitudinal movements of the two wire runs are opposite to
each other and therefore can have a compounding effect.
Designers shall ensure that the minimum electrical clearances are provided for in
OHW designs for the full range of design conditions. Where practicable, crossing of
bare conductors of different electrical sections should be avoided. For example,
where a portal or cantilever mast is available in a switched overlap, the connection
between the switch and an OHW conductor shall utilise insulated cables (rather
than bare aerial conductors) when crossing another conductor of a different
electrical section. The Design Check process shall include checking for provision of
adequate electrical clearances.
Electrical clearances must be checked as part of the Construction, Commissioning
and Handover processes. The Construction Engineer shall ensure that the physical
configuration is in accordance with the approved design. The Commissioning
Engineer shall ensure that the as-built configuration has been checked for adequate
clearances under all operating and maintenance conditions. If there is any doubt
that some of the clearances may not be adequate at or near operational limits, the
clearances and the ambient temperature shall be measured and recorded. The
measurements are to be forwarded to the RailCorp Principal Design Engineer,
Mains for his acceptance within seven days of commissioning.
Typical locations where there is a high risk of inadequate electrical clearances
include:
Audience
• OHW Construction and
Commissioning staff
• OHW Maintenance staff
• OHW Designers
Main Points
• Minimum electrical
clearance between different
electrical sections shall be
provided for in Design and
checked in Construction
and Commissioning
• Crossing of bare conductors
of different electrical
sections should be avoided
as far as practicable
Contact
Neal Hook
Disclaimer
This document was prepared for use on the RailCorp Network only.
RailCorp makes no warranties, express or implied, that compliance with the contents of this
document shall be sufficient to ensure safe systems or work or operation. It is the document
user’s sole responsibility to ensure that the copy of the document it is viewing is the current
version of the document as in use by RailCorp.
RailCorp accepts no liability whatsoever in relation to the use of this document by any party, and
RailCorp excludes any liability which arises in any manner by the use of this document.
Copyright
The information in this document is protected by Copyright and no part of this document may be
reproduced, altered, stored or transmitted by any person without the prior consent of RailCorp.
Distribution
Open
Last Open Distribution
ETN 11/03
Page 1 of 2
Electrical Technical Note
Minimum Electrical Clearance
for 1500V dc Overhead Wiring
01/11/2012
• Switching and feeding arrangements – Clearance of bare aerial feeders to catenary wires, droppers, inspan feeders, cantilever pipes, etc
• Open overlaps
• Overlaps and turnouts where a conductor may be in close proximity of a cantilever pipe or other OHW
support and registration hardware
• OHW anchor pennants wires that may be near an OHW structure or fittings
• Overline bridges
• Tunnels
Actions
• OHW Design Check Lists shall be established by Design providers. Check Lists shall include checking of
provision for adequate electrical clearances.
• Construction quality assurance check sheets shall include the checking for adequate clearances.
• Adequate electrical clearances under all operating and maintenance conditions shall be checked during
the Commissioning and Handover processes.
• All relevant design, construction and maintenance staff are to be briefed on this ETN.
Neal Hook
Chief Engineer Electrical
1/11/2012 © Rail Corporation
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