Table 11 – St950 Elv 48V Current Capability - Siemens ST950 Handbook

For the theoretical junction (Figure 11) this would be:
One lamp per signal head @ 12W x 12 signal heads
Wait indicators at 7W x 4 at 20% duty cycle
Regulatory Sign at 7W x 1
Total average signal lamp power is:
For the theoretical junction, using the figure obtained above (179W), one transformer
would be required.
A single 20A lamp supply transformer is required to power a 20A controller using up to
three LSLS Cards. Two 20A lamp supply transformers are required if more than 20A or
more than three LSLS Cards are required.
The table below summarises the current capability provided by one or two 20A
transformers, the number of LSLS cards each can support and the typical number of
phases and signals heads†:
LSLS 2A Output
Cards* Switches
1 32
2 64
3 96
2 64
3 96
4 128
5 160
6 192
Table 11 – ST950 ELV 48V Current Capability
* Refer to section 4.9 on page 44 for limits on the number of LSLS Cards supported.
† Assuming 12W 48V Helios ELV Signals, 20A allows for approximately 80 signals
which will normally mean that 80 signal heads can be supported since usually only one
aspect of the phase is lit at any one time. Since the short 2 second Red plus Amber
period never occurs on many signals at the same time, the transformer is designed to
cope with a short period of overload. A range is given because of the range on the
number of phases; e.g. 9 phases would allow an average of 10 signal heads per
phase, but with 16 phases this drops to an average of five signal heads per phase. The
figures will be lower if a large number of pedestrian signals are fitted since the current
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Version 4
Last Editor Paul Cox
Document Name ST950 General Handbook
Copyright © Siemens plc 2015. All Rights Reserved.
Phases Lamp Supply
(approx) Transformer
1 – 8 20A
9 – 16 20A
17 – 24 20A
9 – 16 2 x 20A
17 – 24 2 x 20A
25 – 32 2 x 20A
26 – 32 2 x 20A
26 – 32 2 x 20A
Mobility Division, Traffic Solutions
Sopers Lane, Poole, Dorset, BH17 7ER
144W
5.6W
7W
157W
Max. Lamp Av. Signal Heads
Current per Phase†
20A >10
20A 5 – 10
20A 3 – 5
40A >10
40A 7 – 10
40A 5 – 6
40A 5 – 6
40A 5 – 6
Page 50 of 107
Status Issued
Date 16-Jul-2015
Document No. 667/HB/46000/000
Mobility is a division of Siemens Plc