Thorn 'Precinct' OC 1070.T

Bulkhead acquired in April 2011.

Brand new and boxed, this Precinct was an eBay win. I was pleased to find this fitting, as the Precinct (particularly, the SON version) is another of my favourite designs, so to find an unused example makes this a very welcome addition to the Collection.


The Precinct arrived in its original box - even without opening it, there are several clues that indicate the contents!


A couple of line drawings are displayed on the side of the box, including one that shows two closely-spaced Precincts lighting some kind of goods depot where the delivery vehicles never move!


The Precinct was part of Thorn's 'Sentinel' range of security and amenity products. Also included in this range was the 'SONPak' floodlight.


Carefully removing the bulkhead from its box reveals that (as expected) its matte black paint finish is unfaded, and, more importantly, the polycarbonate bowl is not discoloured. Compare this to my used MBF Precinct to see how the fitting ages over time. An alternative option to wall-mounting this fitting would be to install it on a 76 mm diameter column spigot, using an additional adaptor (not supplied with the bulkhead). The adaptor could be used for both single fittings, as well as back-to-back double fittings.


The bulkhead's canopy is flat, and its edges (except for the front) are at right angles to the sides.


A single 20 mm diameter knockout is provided on the underside of the fitting, for use when the back-entry knockouts could not be utilised.


The bowl makes up the majority of the bulkhead's front. A single slotted screw secures the bowl to the Precinct's body.


The two eponymous back-entry knockouts can be seen here; there is no third knockout on the right-hand side, as this is where the main connector block is situated within the bulkhead. Three fixing holes can be seen on this back plate. When the post-top adaptor is used, a gasket is supplied that fits into the indentation that can be seen around the perimeter.


With the securing screw unfastened, the bowl is free to hinge downwards. A Thorn-branded SON-E lamp, dated to August 1983, was included with this fitting. For more photographs of the lamp, please click here.


Inside the Precinct, the E27 lampholder is mounted centrally; it is fitted to the rear section that also houses the control gear and then emerges through a hole in the lamp area. The two captive screws located either side of the lampholder secure the gear section to the rest of the assembly.


The identity label is located bottom-left. In my mercury version of this fitting, the information is provided on an aluminium plate that is pop-riveted to the body.


The 'classic' Thorn logo is moulded into the inside of the casting.


With the gear section removed, the hole that the lampholder fits through can be seen.


Looking the other way, we can see that the aluminium here is largely unpainted - it not being visible when the bulkhead is installed. A further couple of cable entry knockouts can be seen on the vertical sides of the casting.


The entire back section that houses the gear is released when the screws are removed. In order to access the connector block, the two slotted screws at the far sides of the lampholder support plate must be removed completely, and the lower two screws loosened, so as to allow the plate to hinge forward.


Doing just that allows a clearer view of the ballast (which still retains its electrical test stamp, and only just fits within the housing!), ignitor and capacitor. The Thorn designers did well to accommodate these components into a relatively small space, all those years ago.


The capacitor is dated to October 1982. Given the date of the lamp, the Precinct is therefore likely to have been assembled in late 1983 or early 1984.


When powered up, the Precinct resembled how its mercury counterpart looked during operation - though, in the case of the latter, this was due to the bowl being yellowed!

Lamp warm-up video:

Testing the lantern with my energy monitoring device revealed the following results:

Test Voltage (V) Current being drawn at full power (A) Measured wattage (W) Apparent Power (VA) Frequency (Hz) Power Factor True Power (W) Difference (W) Percentage Difference
241.1 0.43 88 104 49.9 0.85 88.12 18.12 25.89




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