Coughtrie BB 15

Bulkhead acquired in November 2013

Another of Coughtrie's extensive range of very tough outdoor lights, the BB 15 was designed to accommodate a single GLS lamp, although there is space within the bulkhead for even an 18 W SOX lamp (with control gear installed remotely), to be fitted, should the need arise.


The bulkhead is roughly oblong in shape, with each edge having a slight curve, in order to match the curved edges of the bowl. Four slotted screws secure the bowl frame to the base. These are slightly recessed into the frame, in order to prevent the screws being removed by hand.


The bulkhead comprises an aluminium base and bowl frame. The deep bowl itself is made of thick translucent glass. From this angle, the bulkhead resembles the mythical Thorn Beta 3 lantern.


As with many Coughtrie products, "J. & G. Coughtrie Ltd. GLASGOW" is cast into the rear of the base. A 20 mm conduit coupler can be seen emerging from the lower cable entry point. The other four entry points (including one for back entry) are unused, suggesting that this bulkhead was either at the end of a system of lighting, or individual bulkheads along the route were spurred off from a main conduit run. Four fixing holes are provided for securing the bulkhead to a wall or ceiling.


"Coughtrie Glasgow" is also visible in the casting for the bowl frame. This view reveals some of the corrosion that has appeared in the aluminium - it is only surface corrosion and doesn't appear to have affected the material.


The bulkhead's part number features at the other end of the bowl frame.


The insides of the bulkhead are almost the definition of simplicity  - the supply cable terminates directly into the lampholder, rather than connecting into a separate terminal block. Although there is provision for an earth connection, when this bulkhead was made, this would have been optional - assuming that the bulkhead was attached to a steel conduit, the earth connection have been provided through this. Modern wiring requirements would require a dedicated earth connection regardless of the material housing the wiring system. Judging by the dried-on water patch to the left of the lampholder, this bulkhead would have been operated vertically, with the lampholder positioned at the bottom of the fitting.


In June 2014, the bulkhead was stripped down to its component parts, in readiness for restoration in the future.


At the top of the picture, an envelope containing the bulkhead's screws and lampholder support brackets (essentially, 'easily losable' items!) can be seen. The thin white object to the left of this is the gasket that ensures a firm seal between the bulkhead body and the bowl support frame. The thin, darker object is a piece of the rubber gasket that was placed between the frame and the bowl itself. This had hardened with age, and had to be broken in order for it to be removed. This piece has been retained, in order to ensure that the replacement gasket is the same width and thickness as its predecessor was. The conduit coupler that had been fitted was removed using a set of mole grips, and a 20 mm diameter hole drilled in the rear cable entry position, as this is where the supply cable will enter the fitting once it is installed.


With this gasket removed, more corrosion was visible on the inside of the frame. Again, this will be addressed at restoration.


The part number of the frame ('C 466') is displayed adjacent one of the bowl retaining lug positions.


The plastic stoppers that had been inserted into the two unused cable entry slots on the two short edges were stuck fast, but as they were already in a very brittle condition, I simply smashed out the centres of both, and removed the remainder using a junior hacksaw placed through the hole. Although these entry points will not be utilised, they will be re-plugged (using brass stoppers this time). The threads were heavily corroded and could therefore hinder the replacement stoppers from being fitted easily; therefore, the opportunity was taken to re-thread the it was, I almost ended up breaking the re-threading device in the process!

Restoration of the bulkhead commenced towards the end of 2016, with the aluminium components being sent away for bead blasting (in order to remove the surface corrosion) and repainting; these returned in early December. A slightly darker shade of grey (I understand from others that there are fifty from which to choose..!) was applied to the exterior, than had been applied originally. The interior was repainted in gloss white.


A last-minute change of plan meant that the rear cable entry hole that had been drilled was no longer required; a 20 mm closed grommet being used to plug the hole.


The majority of the internal components were then re-fitted. A PVC conduit adaptor was screwed into the previous cable entry hole.


Brass stopping plugs were fitted into the other two cable entry holes.


A lampholder (and lamp) were then placed within the bulkhead's interior...yes; that is an elliptical discharge lamp that is fitted - a 35 W SON lamp to be exact! Owing to my decision to use such a lamp, an E27 lampholder was used instead of the bulkhead's original bayonet lampholder.


After applying a replacement gasket strip to the bowl frame, the bowl itself was re-fitted.


With the bulkhead re-assembled, the time had arrived for it to begin its second bout of useful service; thus, it was fitted to the back wall of the house, as an alteration and extension to my existing outdoor lighting setup, on Sunday, 11th December 2016. An enclosure designed for outdoor environments was fitted nearby, in order to accommodate the control gear for the lamp. Incidentally, 35 W SON lamps are NOT suitable for use on 35 W SOX control gear circuits (or vice-versa); the operating voltage of a 35 W SON lamp is 87 V, compared to the 70 V for the equivalent SOX lamp.


A relatively uniform light distribution was observed when the lamp activated later that evening. Surprisingly, even after a few hours' use, the bulkhead did not feel especially warm to touch.


Testing the bulkhead 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
241.9 0.23 43 56 49.9 0.77 42.84 7.84 22.40%

Warm-up video:




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