Yes, mechanical timeclocks can jam (and there's one on the next street from me that has a habit of doing that... it's just been fixed a couple of weeks ago by the night crew, but had been on for about 3 weeks 24 hours a day). Having a close look, those cells do look like blanker cells.. so surely the quick fix here is to install NEMA cells on the suitable lanterns (not the GEC Z9480 as that has no cell at all) or fit a new clock in the master column. Yet somehow this seems not to be possible.

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Alot of Sheffield's residential and some main routes are Group Switched. Most of the replacement lanterns (originals having no cells) have blanking cells fitted which is bizzare considering the age of the original switchgear.

That's solved that mystery then! What a strange way to light the roads in this day and age but that's Sheffield for you  

It's funny you should bring up this area in Sheffield as I actually live just around the corner. They use really puzzling setups, sometimes you see older installations on photocell-controlled group switch circuits yet more modern installs on time-clocks. I've been exploring that area for a long time trying to locate the control point for the lanterns on my road with no luck. Then again, they stick as many lanterns as they can fit onto a single group so finding out what actually happened to all those lanterns could forever be a mystery!

It is most likely that without a column key, you won't find the control point - as there'll be one column with a clock in it that is controlling the street. The only other option is to go along a street at a really quiet hour like 2am, and walk slowly past each column to try and hear any whirring or clicking noises to give away a timeclock inside.

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You may find that the control point is actually inside a sub station somewhere. Sometimes the clock may be inside the sub itself, or in a pillar next to the building. If this is the case then maybe a lack of authorisation means that nobody from the lighting crews can access it to repair? The lights that are not dayburning may have the cells still connected, or they may be jointed off the main rather than the 5th core, and so are individual... Interesting stuff all the same.

I wonder if there's any clock in this compound? Seems right area....
http://maps.google.co.uk/maps?q=Orgreav ... ,2.15&z=16

It makes sense. On google streetview, the lanterns that are fitted with actual photocells rarely appear to be dayburning where as those that are groupswitched (either have dummy cells or no cells), there seems to be MANY cases of dayburning strings so maybe the group cell or clock is in the substation meaning the council don't have easy access to stop them dayburning. So I agree Gramma6, it definitely seems to explain how many lanterns dayburn in Sheffield  

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"I used to rule the world... Now I sweep the streets I used to own."
Remembering GEC.

It would make sense especially if the dayburners are connected to a 5th core as Versalift suggests

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The Dutch seem to group swich whole villages,
Never seen a dayburner over there!!