Siemens ST950 Handbook page 57

thresholds for conflict or correspondence monitoring. It is therefore essential that
individual ground returns are used for each green signal.
3. The allowable lamp load per cable run is defined in the following tables. Refer to
Table 8 – ST950 ELV 48V Lamp Load (Watts) on page 45 to determine the total
lamp load connected to each drive cable and each return cable.
For each 'out-going' drive cable, determine the total load of all the signals supplied
by that cable. This will typically be a single aspect (e.g. one Helios ELV signal) but
could be higher where a green drive also powers a tactile unit for example.
A single LED signal return core (equivalent to the neutral in an LV system) is to be
provided for each Red, Amber Signal Head (or Nearside Red / Green Signal). A
separate return MUST be provided for the green aspect. Where a common return
core is used, the highest lamp load that may be illuminated at any one time needs to
be determined.
For a UK traffic signal head, one Helios ELV lamp load 12W is considered the
highest for the return cable since only one aspect is ever illuminated; the short
red/amber period can be ignored.
For a near-side pedestrian signal head, the figure is one near-side signal unless it
shares the same return with a Demand Indicator or a Tactile Unit.
Example, assuming a distance of 180 metres using 1.0mm
Near-side ped drive cables: 18W each at 180 metres = 2 cores (each)
Ped demand indicator drive cable: 6W at 180 metres = 1 core
Common return cable for all BUT green aspect: 24W (6W+18W) at 180
metres = 3 cores
Green aspect return cable 12W at 180metres = 2 cores
4. If required to minimise core usage it is permissible to common signal returns on the
same pole as long as the total lamp load dependent on that return is considered and
the cable length limitations defined in the table are observed. For example, two 12W
RAG traffic signal heads require that a load of 24W is considered with a common
return cable. (Note: please also consider the comments given in paragraph 1)
5. Regulatory signs should normally be cabled with a separate drive and return core.
Where more than one regulatory sign is fitted to a pole, the drive and return for
these may be common, as long as total load dependent on those cables is
considered and the cable length limitations defined in the table are observed.
If required to minimise core usage it is permissible to common regulatory sign and
traffic signal returns on the same pole as long as the total load dependent on that
return is considered and the cable length limitations defined in the table are
observed.
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
2
cable:
Page 57 of 107
Status Issued
Date 16-Jul-2015
Document No. 667/HB/46000/000
Mobility is a division of Siemens Plc