Wiltshire has been using the Telensa RF node switching for the last couple of years and employs selective part night operation in some regions. However my village is too rural to be within reliable range of the base station in Salisbury, so conventional photocells are employed, as a result I haven't been able to witness the switch on regime for the Telensa system.
However a trip into Salisbury this evening coincided with switch on. I had assumed the columns would be switched on either by large zones (like the Mayflower system in Hampshire) or at least on a street by street basis.
However, the switch on is staggered not only by street, but
within each street. Salisbury still retains SOX, and in these locations, it is clear to see that each lantern has switched on at a different time as they were all at different stages of warm up. This is repeated on SON lit streets, it was rare to see consecutive lanterns lit, it was all random.
Some element of zone control is also in use as in some areas, SOX was only just turning on, where as in others, it had clearly switched earlier.
It may be possible that I witnessed the all night or perhaps the part night lanterns being switched in individual groups, which may explain the non uniform pattern. However I wonder if each node has a random timer function built into it, so that actual switch on is random after triggering?
Such a function would prevent power surges, especially since Wiltshire retains legacy lanterns with magnetic gear and hence high in rush currents.
The South Coast PFI utilises electronic gear lanterns which are inherently "soft start", so switching large groups of lanterns at once is unlikely to cause supply side surges.
I wonder how the switch on is implemented in Essex which also uses the Telensa system? Perhaps David can enlighten us..