Electricity + Control October 2017

CABLES + ACCESSORIES

The Pratley family: Top: Kim Pratley – son of George Montague Pratley and CEO of Pratley; Kim’s wife, Val; their sons Charles, and Andrew.

When it comes to pure price, it's useful to express the dif- ference in price between vari- ous cable glands in terms of an

Brilliant engineering IURP D SUROLÀF inventor.

ens according to the slightly finer pitch on the oth- er thread. The nett result is a virtual thread whose pitch is the difference between these two pitches. This virtual thread can be made infinitely fine. The upshot is a gland with two relatively coarse pitch threads but which achieves a very fine pitch thread action without suffering any of the fine thread draw- backs. This results in an incredible cable armour clamping force even with a very modest tightening torque. Indeed, an adjustable cable gland can often outperform specification slip load tests when just hand tightened. It's like having a built-in gearbox. The adjustability and differential thread action are made possible by incorporating a loose cone bush. This has many other technical advantages as well. It can self-centre under the wire armours to achieve the best average grip position and it renders the armour clamping both visually verifiable and in- dependent of axial movement of the cable during tightening. This latter effect is a common cause of cable gland pull out failure from ordinary glands. Price is different to cost and when considering total cost, the integrity, reliability and longevity of installations are important parameters. So too is the often ignored time cost of the labour required to install specific items. Large projects may involve thousands of cable glands. If it takes just five min- utes longer to fit an ordinary cable gland, that's ten extra artisan days per thousand glands fitted.

equivalent length of cable. For a typical PVC 4 mm2 x 4 core armoured cable the cable length equivalent of the price difference between a top quality adjust- able gland and the very cheapest eastern import is a mere 9 cm of cable. Coincidentally, this is also the equivalent cost of about one minute of artisan time. If on a particular project the average cable run was say 25 m, the price saving would be just a fraction of a percentage of the cable price. The cost saving on the other hand would be negative. Conclusion Given all of the technical advantages, installa- tion cost savings and lifetime cost savings and of course the extra margin of safety, the use of Ad- justable Cable Glands for terminating armoured cables makes good sense. Complexity can solve most engineering problems; simplicity howev- er requires more skill. The design brilliance of Monty Pratley's Adjustable Cable Gland lies not in complexity but in its elegant simplicity.

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Eldon Kruger is Director: Marketing at Pratley.

Andrew Pratley

+27 (0) 11 955 2190 agap@pratley.co.za