215B. Off Bath Road, Bridgwater, Somerset With thanks to Dwight for informing me of these Survivors. On the roadway leading to the industrial estate that once formed part of the British Cellophane factory (1937 - 2005) are four 25 ft (8 m) GEC ZP1000 concrete columns dating from the late 1950s or early 1960s; each supporting a Z8430 lantern, which was designed for running a single 250 - 400 Watt MA/V (medium pressure mercury vapour) lamp. As these lamps could only be operated vertically ordinarily, the lantern included a magnetic arc deflector that ran in series with the supply to ensure that the arc tube would not rupture when operated horizontally. This problem was short-lived, however, as very soon after that, the high pressure mercury vapour lamp (MB) became available, which eliminated the restricted lamp burning positions, thanks to the use of a quartz arc tube instead of glass. With a fluorescent coating to its outer bulb, the whole output parameters of the mercury lamp changed, leading to GEC re-launching the Z8430 as the Z8430CM; the suffix representing "Corrected Mercury", which featured a redesigned prismatic glass bowl that was optimised for the new technology.
The first column is installed a short distance up the access road. There may have been additional columns closer to the entrance originally, but may have had to be removed owing to proximity issues with an overhead high voltage electricity transmission line.
These columns employ the shorter outreach version of the bracket.
The original Z8430 bowl featured a series of concentric circular refractor prisms. With the rapid obsolescence of MA/V lamps after the Z8430 was brought to market, these are the rarer variants. As can be seen, an MBF-type mercury lamp is employed within the lantern these days.
The other three columns are pictured below, with the middle one having lost its bracket at some point.
A slight amount of spalling had occurred to the foreground bracket too, but not at the column end.
The missing bracket now provided a perfect perch for the on-duty Wood Pigeon sentry guard!
The final column was located just inside the security gates.
This example appeared in good condition too.
A column that once supported some sort of post-top lantern was installed between the two gates, while a sleeved ZP1000 further inside the site now supports floodlights.
Viewing the second column again, from the adjacent Regal Walk, reveals that its inspection door is missing.
Zooming in reveals some rather weathered control gear, along with porcelain fuse carriers on both the live and neutral supply wires, as was common practice in wiring of the period.
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