Thorn Beta 5

Lantern acquired in March 2011.

This lantern came from column 36561 on Vicarage Road, Mickleover; its removal brought about by a relighting scheme as part of Derby's Street Lighting PFI in February/March 2011. Owing to an unexpected road closure brought on by National Grid Gas, the lantern remained in service for a little longer than had been originally proposed. Once the gas work had been completed, the outgoing columns were quickly disconnected and the replacement columns connected up. The lantern was then removed, along with another top-entry Beta 5 from column 36545, on Thursday, 10th March. Both lanterns were picked up the following day. Following the removal of these Beta 5s, there are now NO top-entry lanterns installed on public roads in Mickleover, though a (derelict) example exists on a lane just off Western Road; this is in private ownership.

The inventory record for this lantern (as it appeared in 1997) is displayed below:

Unique Number: 36561 Location: JNC FENTON RD
Postcode: DE3 5EA Road: VICARAGE ROAD
Road Number:   Parish: MICKLEOVER
Sequence Number: 20 Patrol: Y06
       
Lamp Type: SXPL2 Wattage: 35  W Control Type: PE1E
Lamps/Lantern: 1 Lanterns/Unit: 1 Control Setting: 4
Lantern Type: TE Lantern Manuf:   Control Gear:  
Height: 5  m Support Type: CC CONCRETE COLUMN/PILLAR
Bracket Proj'n.:    m Support Finish: U UNPAINTED SUPPORT
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 : 36551 / Circuit: 1 / Seq: 7
    Location : ON GREEN ENT TO PK        
    Road : VICARAGE RD        
    Parish : MICKLEOVER        

IGN CELL 14/2/96 WS 403081 (Take note of this - it may prove significant later in this page...)

The first few photographs, taken in February 2010, show the lantern whilst still installed. It would be another year before this installation was replaced.

     

The reason why a top-entry lantern was fitted to a side-entry sleeve bracket is unknown - it is these quirks that will be missed when a uniform street lighting style exists throughout Derby.

 

Moving to February 2011, and the installation was now surviving on nothing more than borrowed time...

 

Aside from the lamp's outer bulb blackening becoming worse over the twelve months, the lantern looks unchanged.

 
 

Amazingly, the lantern unscrewed from the top-entry elbow when removed from service - even the 3 mm grub screw that kept the lantern correctly orientated on the threaded pipe was free.

 

By the time that this lantern was made, one-part photocells were increasing in popularity; hence the alteration made to the aluminium canopy (in order that the NEMA socket is located horizontally on the lantern) from earlier versions of this lantern.

 

Although the NEMA socket is normally located in the centre of the casting on side-entry examples, it has to be positioned at the extreme end of the casting, in order to avoid the photocell fouling the overhang of a top-entry bracket. This position is also away from the lantern's gear tray.

 

A curious point to consider is that the bowl securing clip is always located at the 'front' end of a Beta 5, and the bowl hinge is at the back. However, as the NEMA socket end of the lantern needs to be positioned towards the 'road' side on the top-entry version (as a photocell would not fit beneath a bracket), this version of the Beta 5 has to be installed 'backwards'. Not that this would noticeably alter the lantern's output, of course.

 

Several refractor prisms are moulded into the lantern's bowl. Although Thorn later produced a slim-line version of the Beta 5, complete with shallow bowl (that featured no refractors beneath the lamp), the top-entry design was never modernised. It is unknown when production of the top-entry Beta 5 was discontinued, although it is likely to have been in the early-mid 1980s.

 

As the above 'installed' photographs demonstrate, the outer bulb of the lamp fitted in this lantern was beginning to blacken. A hand-written installation date (not visible here) on the neck of the lamp shows that the lantern was last re-lamped in April 2008, so the lamp would have required replacement in 2011 anyway.

 

A classic Thorn label is attached to the corner of the gear tray.

 

With said gear tray unfastened, the extremely clean inside of the canopy becomes visible. The lantern's cable clamp is as new; having never been used. Notice that the wire from the lantern's main connector block to the NEMA socket has been replaced - this new wire would have had red insulation originally. Lengths of tape hold the gear tray supply wires together (or at least, they would have when new - their adhesive properties are now non-existent!) for neatness.

 

At least three different versions of the top-entry Beta 5's canopy had been produced by the time that this lantern was made - as can be seen, this is "Impression C". Always leave on a good impression, that's what I say.

 

As always, the ignitor and capacitor are positioned at one end of the gear tray, and the ballast at the other. As stated in the lantern's inventory record above, the ignitor is a replacement; having been fitted on Wednesday, 14th February 1996. The lantern's photocell was also replaced at this time; however, the lantern ended its days on the road with a Royce Thompson Monostar 1000 photocell fitted. This dates from 2001, and so, the cell fitted in 1996 was only in use for a maximum of five years. The heavily-yellowed capacitor carries a manufacture date of 1982 on its casing. A hairline crack exists in the capacitor's plastic casing, but may still work.


Almost five years after entering the collection, the lantern was fitted to an AC Ford AC 184 wall bracket on Friday, 12th February 2016. No restoration or cleaning had taken place during this extended hiatus; indeed, the lantern was installed in as-removed condition - even the lamp with its blackening outer bulb was re-used. The only modification made was to the lantern's NEMA socket - this was wired out in preparation for the fitting of a new supply cable.

 

When connecting the new cable, I did attempt to release the cable clamp; however, its fixing screws were too heavily corroded, with the result that they would not loosen, and that, consequently, the clamp could not be used. The official earth connection screw was in a similar state; it also having never been used, owing to the earth being connected to the screw that secures the gear tray's fixing pillar instead. This alternate point was used for the new cable's earth connection as well. Despite the blackening to the outer bulb, the lantern's output was not affected too badly.

 

The blackening towards the rear of the lamp was more pronounced than it was at the front, though even from below, this didn't seem to affect the lantern's performance. Over time, the blackening will spread over the entire outer bulb, and will, eventually, render the lamp too dim to produce satisfactory light levels, even if its arc tube is still healthy. In all-night operation, this process could occur over a few months; however, in the Collection setting, the process is likely to take far longer than this.

 

Testing the lantern with my energy monitoring device revealed the following results; needless to say, the capacitor did turn out to be defective:

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
238.1 0.56 59 133 49.9 0.45 60 25 71.43%

Lantern warm-up video:

GEC 'Dioptrion' Z8431 | Wardle Murray

Thorn Beta 5s in the Collection

C. 1965

1982

1983

1989

1996

2001

2004

2006

2008


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