Thorn Beta 5

Saving one lantern from a column is always fantastic. Saving the lantern that replaced a lantern that then entered a Collection (are you still following?) must be a very rare occurrence indeed. However, this is exactly what happened here - the Beta 5 replaced my first GEC Z5698U on the 14th May 2003, but was itself replaced in April 2010, due to the commencement of the Derby Street Lighting PFI in Mickleover. This lantern and its associated column (60556) were earmarked for replacement, and so I decided to try to save this lantern for the Collection, owing to its history being known. Thankfully, I was successful in acquiring the lantern after the column had been disconnected, and so, on Friday, 7th May 2010, I picked it up from the depot.

The following is the inventory record for this installation. This record is as it was in 1997, when Derby City Council took control of its own street lighting repairs from the County Council, and when the Z5698U was still fitted, of course. Therefore, any changes made after this date (including the change of lantern type in 2003) are not shown.

Unique Number: 60556 Location: O/S NOS 5/7
Postcode: DE3 5NT Road: WENLOCK CL
Road Number:   Parish: MICKLEOVER
Sequence Number: 3 Patrol: Y06
Lamp Type: SXPL3 Wattage: 35 Watt Control Type: PE1E
Lamps/Lantern: 1 Lanterns/Unit: 1 Control Setting: 4
Lantern Type: PT Lantern Manuf:   Control Gear:  
Height: 5  m Support Type: TS TUBULAR STEEL - PAINTED
Bracket Proj'n.:    m Support Finish: P PAINTED COL/SIGN/PILL/GANTRY
Bracket Type:   U/G or O/H: U UNDERGROUND
Board Code: E76 Status Code: 0 USUAL / NORMAL
Service Owner: A Is this lamp/sign an Isolation Point ?: N
EB Order number:      
No-supply sheet: 0 Isol Pt:   / Circuit:   / Seq:  

The first couple of pictures show the lantern about a month after installation, in June 2003:

Keep an eye on the yellow writing beneath the lamp in the picture below...


Fast-forward to 2010, and by the time that the following photographs were taken, the Beta 5's days were numbered; indeed, by the time that the right-hand picture here was taken, the supply had been transferred from the outgoing column into the new column - proved by the dayburning lantern on the new column! Shortly after this picture was taken, the Beta 5 was removed and returned to the Balfour Beatty offices for safekeeping until I could retrieve it. The dayburning new lantern was also repaired at the same time. An interesting point to note was that, with the lantern removed, the section of the bracket that had previously been inside the lantern (and thus not exposed to the weather) retained a more glossy paint finish than the rest of the bracket did.

I eventually picked the lantern up on Friday, 7th May 2010. Despite the lantern being almost seven years old when removed, it still retained a reasonably 'new' appearance.

The slim appearance of this version of the Beta 5 is very apparent here.

The Beta 5 (along with sister lantern, the Beta 2) retained its die-cast aluminium canopy until production finally ceased in 2008. The increasing cost of aluminium, combined with decreasing orders for these lanterns, was probably what finally sounded the death knell for Thorn's once-popular side-entry SOX lanterns.

The lantern's bowl was still reasonably clean upon leaving service, though I did wash it out before taking these photographs. Remember the yellow lettering mentioned above? It's still just about legible!

The portion of the capacitor that is visible with the gear tray secured is rather yellowed. SOX lamps do not emit ultraviolet light, so the yellowing can only be caused by exposure to sunlight, although even this would be limited at best, owing to the capacitor's recessed position.

With the lamp removed, various unused screw holes can be seen on the reflector/gear tray; their use dependent on the make and type of gear fitted to that particular lantern.

The wiring is exactly as it was when the lantern was fitted in 2003, except that the sections of wire that pass directly over the ballast are a little discoloured because of the insulation being slightly melted by the ballast during the lantern's operation. The ballast in this lantern is higher than those fitted to earlier Beta 5s, and so there is a greater chance that the wiring will come into contact with the component, as has been the case here.

The components in this lantern are identical to those fitted in my Gamma 6 dating from 2001, though this isn't surprising; the Beta 5 was made in the same year. Interestingly, the positions of the ignitor and capacitor are transposed in my Beta 5 dating from 2004.

Returning to the paint pen markings applied to the reflector, 'JPS' is 'Jeremy Skertchly'; 'MB' is...well, let's just say that I always dreamed of seeing my name in lights, but this wasn't quite what I had in mind!

The Monostar 1000 cell is also marked up accordingly - if nothing else, this proves that the cell was never changed during the lantern's short lifetime.

The Beta 5 was installed on an AC Ford AC 872 wall bracket that was sandwiched (literally!) between the Atlas and Thorn Alpha 3s.

With the cell disconnected, the lantern was then powered up:

Lantern 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)
240 0.57 55 137 49.9 0.39 53.35

These results prove that, despite only being in use for seven years' worth of nights, the capacitor was faulty.


Thorn Beta 5s in the Collection











Thorn Gamma 6 | Simplex Aries




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