Posted By Martin Daly Why don't you try using lasers. Martin Daly

Posted By John Caboche Somewhat strangely I find myself in agreement with Bob :-) Not many people can CAT scan properly, I think his estimate of 50 - 60% may be somewhat conservative. I have a lot of experience hammering in road pins (and CAT scanning too) - I used to be a chainman and site engineer and still carry the scars where the sledgehammer slipped on more than one occasion. In reality the chances of hitting a cable are low but are there, there is very little alternative in reality to using pins, both for minor estate type roads or a major highway construction, the blacktop gangs rely on the pins/kerblines to level in the blacktop. The only things that can be done are desktop services studies and CAT scans - if there is a major issue with services then ground penetrating radar can be used, most contractors will not go down this route due to the large costs involved. There is also the possibility of trial holes but this is impractical on larger jobs simply due to the large amount of pins required, and even on smaller jobs would be a major hassle. Network Rail have a standard/procedure as there is an serious issue in the railway environment with cable strikes - especially involving signal and HV cables - and to sum it up it requires the control measures above coupled with a "permit to dig" system. There isn't really an alternative as far as I can see, no matter what control measures you put in place there is always going to be the possibility of a cable strike. Statistically the possibility of a strike verses the amount of pins hammered (locally or nationally) is probably way below the HSE's requirements for sensible risk management.

Posted By AlB No one has answered Martin's point. Why not use lasers - would eliminate the need to use pins. Would be cheaper in the long run as well.

Posted By John Caboche In short lasers don't go round corners, change in level and as Bob has pointed out can be disrupted by sunlight and plant. They are also a bit inaccurate as well in terms of the detector's sensitivity. They are totally impractical for this activity, they are useful for mass digs for setting an approximate level and they are useful for giving line and level on pipe runs - although these are two very different types of laser systems. Believe it or not pins and string are still the best way to lay out kerblines and roads.

Posted By Kenny McGillivray Hi Kevin Long time ago when I laid bricks for a living and sometimes kerbs, we would set up a 'dead man' at each end of the line, this was either bricks built as a corner or a kerb laid at each end. We then strung a line of heavy fishing gut between the 2 points using a wooden corner block, the fishing gut is less likely to sag in the middle and requires less tightening. You will have to ask a brickie to show you how to make corner blocks but they are easily made from timber 2x2 or similar. regards Kenny

Posted By Robert. Kevin, dodgy subject here. The insertion of pins in the ground still requires a certain amount of force. The risk of damage to a service would still be present and IF the pin went through (eg an HV) cable, it would still have the effect of incurring a short circuit possibly causing burns to the operator. Best practice is still that of location and avoidance.

Posted By Chris Packham Perhaps as a longer term solution we could approach the problem from the other end. Outside our house is a buried power cable for the village. The drawings show it going down the middle of the street. Actually it runs along the edge closest to our house. You can imagine what happens when the water board come to dig a trench. Big flash, lots of sparks, even though we pointed the discrepancy out to them. No power in the village for several hours until the power cable is mended. We finally persuaded the electricity board to run a warning tape in the ground a few inches above the cable. Now when someone digs a hole, they realise what is there before the digger goes into it. If these were done as general practice, then before hammering in the pins a simple hole dug would reveal the cable. Chris

Posted By PeteA It seems everytime the subject comes up of hitting a cable, suggestions of ground radar are always brought up. No Surveying compnay in the country would ever use ground radar for locating power cables (pot end cables maybe) The best way to locate power cables is with electromagnetic technology (cat & genny) providing it is utilised to its maximum. This means using the Genny, Using a CAT on its own is not enough, you should never see someone using a CAT without a Genny in my own opinion. Considering I earn my living by specialising in Cable Avoidance Courses, this might sounds biased, but the main thing with cable strikes is a lack of proper training, almost all the courses I do, the guys who have usually been using locator's for years do not know how to fully utilise the CAT & more just as important the Genny. Forget Radar for power cables, it is to dependant on ground conditions, and all kind of other factors, invest in some decent training.