Specifications

ST900 Family General Handbook
667/HB/32900/000 Issue 12 Page 60 of 265
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 consumed by
the Red and Wait Signals is higher than the current consumed by a single 12W Helios ELV Signal
(see Table 10 on page 55).
3.14.6 Intersection’s Power Requirements for Running Costs Estimate.
3.14.6.1 Introduction
Firstly the Total average lamp power for the junction is calculated. Secondly the
Total average lamp power is added to the Total average controller power. This gives
the Total average junction power, which a local authority may use to estimate
running costs.
Total Average Lamp Power
Total Average Junction Power = +
Total Average Controller Power
3.14.6.2 Total Average Lamp Power
Total average lamp power is calculated as follows:
For every signal head, only 1 lamp is illuminated on average (at 12W assuming
Helios ELV LED lamps), plus every WAIT indicator is illuminated at 7W and every
Regulatory Sign is illuminated at 7W.
Therefore, considering our theoretical junction (Figure 13), we have:
12 signal heads each with 1 lamp at 12W (12 x 12w)
144W
4 wait indicators illuminated at 7W (4 x 7w) 28W
One Regulatory Sign at 7W (1 x 7w) 7W
Total Average Lamp Power is: 179W
3.14.6.3 Total Average Controller Power
Total average controller power is calculated as follows:
Average Controller power + Average Detector Power.
A basic controller is rated at 40W, and for the purposes of this calculation Siemens
ST4R/ST4S detector cards are rated at 3W/card. See section 3.14.7.