Status Issued Date 16-Jul - Siemens ST950 Handbook

Important ELV Considerations
Do not connect any device that has not been specifically designed or
tested for compatibility with the ST950ELV system. If in doubt, contact
Siemens Poole for further information.
ST950ELV compatible equipment such as Helios ELV traffic signals, near-
side pedestrian signals and ELV LED regulatory signs are all clearly
marked "ELV". If equipment is not marked "ELV" then additional care
should be taken to ensure that it is suitable for use in an ELV system.
To provide the most reliable operation, Siemens ELV controllers use a DC
(unsmoothed) lamp supply, which in common with DC powered
telecommunication equipment, is negative with respect to earth so as to
avoid electrochemical corrosion effects.
To maintain all street voltages within ELV limits, equipment outside the
cabinet must be supplied with voltages within the band -48V RMS with
respect to earth. Voltages positive with respect to ground / earth will result
in overall voltages within the system being in excess of the ELV limit as
defined by BS7671.
Care should be taken to ensure that no LV (Mains Voltage) equipment is
installed within the ELV street furniture as this will result in risks to
personnel and risk of catastrophic failure of ELV equipment should such
voltages be applied to the ELV equipment by accident.
The Siemens ELV controller has been designed and proven to meet the
following requirements for Protective Extra Low Voltage (PELV) and the
operation of a signal compliance monitoring system with ELV voltages:
1) The Siemens ELV system is PELV and the earth is connected all the
way through, as allowed for in BS7671 414.4.1. The source is a
safety isolating transformer to BS EN 61558-2-6 as allowed in 414.3
(i). Protective Isolation within the controller cabinet is achieved
between the PELV circuits and those higher than band I by ALL
conductors having insulation rated for the highest voltage 250V, as
mandated for in 414.4.2 (iii), and where the parts of the circuits are
not wires / conductors, then physical isolation as allowed for in
414.4.2 (v) may be used.
Any third party ELV sources installed in this system should follow
the same guidance, re-isolation and insulation and should adopt the
same polarity and voltage range to avoid voltages in excess of ELV
band 1 being present in the signalling / street furniture part of the
system.
2) Terminations are IP2X (British standard finger proof i.e. not
accessible to solid items of 12.5mm or greater).
Security classification Unrestricted
Version 4
Last Editor Paul Cox
Document Name ST950 General Handbook
Copyright © Siemens plc 2015. All Rights Reserved.
Mobility Division, Traffic Solutions
Sopers Lane, Poole, Dorset, BH17 7ER
Page 5 of 107
Status Issued
Date 16-Jul-2015
Document No. 667/HB/46000/000
Mobility is a division of Siemens Plc