Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 12 Page 5 of 265
WARNING IMPORTANT ELV CONSIDERATIONS:
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).
Any third parties making alterations to such equipment / PELV installations must
consider the electrical requirements for PELV and the above in what they do, and
should only attempt such alterations if they are competent to do so.
The controller monitors its signal outputs for both positive and negative voltages
with respect to earth for its conflict system. In order to ensure the ELV voltage band
is maintained, positive voltages with respect to earth are clamped by the controller.
Should a positive voltage be applied to the signal outputs, the controller will
consume current to maintain a maximum positive voltage of approximately 0.8 volts
at the controller terminals.