Depthing Tubes

We have, of late, been in extended communication with Mr Martin Cummins –  an engineer in permanent magnets and a man of considerably piqued curiosity – amply demonstrated to us now that Mr Cummins has turned his inquisitive mind to the mysteries of the telegraph pole.


I bear only a query regarding the grey plastic extruded ducts often seen, placed 180 degrees apart, on telegraph pole bases. After years pondering on same, I finally came to the conclusion that they were either for adding preservative at intervals (Hence cap sometimes seen) or possibly, but unlikely, as an anti-rotation device for where a replacement pole was a close fit in an existing hole – even providing access for a below-ground wood rot check.

Upon request, Mr Cummins furnished us with example photos.  He went on to tell us that his approaches to “Outreach” proved less than fruitless and nobody there had the faintest idea what these “depthing tubes” were for. Though why he thought a mental health charity would be able to help, when coincidentally, right next to them in the phone book he would have found “Openreach” and perhaps a far more illuminating phone call.

 Another depthing tube

He continued…

I have been told that it is a neat device for ensuring correct burial depth, even if the “Birth-line” is incorrectly stamped.  Is this the whole story? and was it an invention of the G.P.O? What is the correct name for the duct, and is the depth rod a purpose made, graduated scale, with perhaps a cursor to rest on the top of the tube, or just a piece of convenient bar, which is chalk marked? Presumably the reason for the height from ground-level is to discourage small children from gravel-filling (Caps as well) or is there another reason? Two tubes, I suppose, in case one gets crushed flat during installation? I have yet to see an article on this system?

Mr Cummins is very thorough in his research and determination to attain complete and total understanding of his subject.

While endeavouring to locate information on these ducts, I came across a reference to a spigot or flat circular mark called a “belly-button” being found on posts, which was put on the straightest side of the post. Perhaps another, humorous term for a birth-mark, but why it is orientated this way is beyond me. Another site refers to the birth-mark as a Doby mark. A strange term-any idea of its meaning?”

Mr Cummins also turned up a whole load of interesing telegraph pole patents; two shed loads about fibre-glass telegraph poles in Dunstable; a fine example of a telegraph pole preservative administering system near Leighton Buzzard; and another unponderable suggestion that BT may well fly kites to raise telephones line over a tree branch.

A telegraph pole armoured ductAll of this though makes me think that Martin is looking just too hard – reminding me of the story of the millions of pounds that NASA spent developing a biro that could write in the micro-gravity of earth orbit – whereas the Russians just took a pencil… You see, I think the answer is much more mundane in that these tubes are just “kick stops”, cable protectors – and nothing more. Intended to save the hardship caused by fluourescently clad council grass-strimming staff from slicing through the cables that run vertically down the pole and into underground ducts. On the left is one I photographed near home showing a protruding wire.  Those as witnessed by Martin Cummins simply being devoid of cable.

I am, of course,  just guessing, and respectfully ask some of the many Openreach and assorted telegraph pole types who frequent these esteemed pages to espouse some of their profound wisdom and tell us, and particularly, Martin Cummins, what the hell these things are for?