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Jon McElwain
06-22-2017, 1:41 PM
I need to measure the height of some power lines at a project I am working on. A laser measurer would be ideal, but I am concerned that it might not be able to see a power line some 20' overhead. Has anyone used one for this type of application? Does it need a larger surface like a wall to get a reading? Do I just need to get the laser to hit the line?

Thank you for your help!

Jon

John Lanciani
06-22-2017, 2:38 PM
I doubt you'll have good luck with a laser due to the size and shape of an overhead wire. This is the correct tool to use, not super expensive if you need accurate measurements; https://www.amazon.com/Ar600e-Digital-Ultrasonic-Height-Sensor/dp/B00UPSXFSG/ref=pd_lpo_sbs_328_t_0?_encoding=UTF8&psc=1&refRID=CQFNH57V44NQWGWDMH71

Charles Lent
06-22-2017, 6:15 PM
Here is a way to get an approximate measurement using only basic hand tools.

If you can set a good carpenters level on something at about eye level above the ground and center the bubble, then place a 45 degree triangle on top of it, and look up the 45 edge of the triangle toward the wire. Then move this triangle and level toward or away from the wire until looking up it's 45 degree edge shows that the 45 deg edge of the triangle is in line with the wire. Then measure the distance horizontally from the level to a point directly below the wire (another level and a square can be used in a similar way to determine this). Add the height above ground of the triangle to this horizontal distance measurement and you will have a close approximation of the wire height. I saw my uncle do this about 65 years ago to measure the height of a tree. I've never tried it myself, but thought it was something to remember that might pay off some day. Of course, if you have access to a surveyors transit you can get a much more accurate measurement.

Charley

Ted Reischl
06-22-2017, 7:21 PM
There are apps available for cell phones that will do it very easily. Try searching "measuring".

John K Jordan
06-22-2017, 7:23 PM
I need to measure the height of some power lines at a project I am working on. A laser measurer would be ideal, but I am concerned that it might not be able to see a power line some 20' overhead. Has anyone used one for this type of application? Does it need a larger surface like a wall to get a reading? Do I just need to get the laser to hit the line?

Thank you for your help!

Jon

How soon do you need to know? I have a Bosch and could check the next time I walk down to the shop if it's not pouring rain (like it is now).

JKJ

John K Jordan
06-22-2017, 9:46 PM
How soon do you need to know? I have a Bosch and could check the next time I walk down to the shop if it's not pouring rain (like it is now).

JKJ

OK, I tried it. The question I have is how big is the wire. Is it really ia high-voltage power line (relatively small gauge) or is it thicker, like a phone or cable TV cable?

A pole with three wires crosses a part of one of my fields, having two higher thinner wires and a lower, fatter cable. My Bosch laser measuring device (an older, now discontinued model https://www.amazon.com/gp/product/B001U89QBU) worked fine on the lowest cable, over 21'. It was close to dusk but I could not see the laser dot on the thinner wires. No problem with the distance - it could easily read the the height of the pole: 28' 0-11/16". If I could have seen the dot, perhaps when it got darker, it may have worked. On the other hand, if the wire is relatively shiny metal it might not reflect enough light back to the sensor making it difficult or impossible to measure.

Another issue: mine requires a button push to turn on the laser then another push to take the reading. No problem with a wall or a 2x4, but it is difficult to hand-hold the device to keep the dot steady on a very small target while pushing the button. I was able to make one measurement by resting the device on a fence post and pressing carefully. The device has a 1/4-20 socket on the back so out away from a fence post I mounted it on a tripod and was able to hold it rock steady on the cable for a reading - just over 21'.

It would be a LOT easier to measure if the laser could target something bigger than a wire. You know how juvenile delinq.., er, inquisitive youngsters used to tie two tennis shoes together and throw them over a line? (Maybe they still do this.) I might consider connecting two tennis balls together with a bio-degradable cord and throw that over the wire. I'm sure the laser could easily target that. Choose the right cord and the pair would come down in the first rain. Choose otherwise and they could be up there for years!

Another possible option, call the power company. Perhaps they have what it takes to measure clearance and would do it for you.

Another possible option, extend a pole to the bottom of the line. I have a couple of 24' insulated fiberglass extension poles. I might tape a few feet of plastic tubing on the top and successively raise the pole until it touched the wire. I wouldn't try this with a high-voltage line in the rain or even when the humidity is high.

Another possible option, tie a helium balloon on an insulated line and raise it (on a windless day) until it touched the wire. I take no responsibility for death by electrocution by pulling a Ben Franklin in a rainstorm with conductive line. I once used a string of carefully placed bunches of helium balloons to measure something non-existent but 250' high at the Oak Ridge National Laboratory for a special project - it's a long story.

And the triangulation method would be the easiest way to approximate the height. It depends on the accuracy you need.

JKJ

Jon McElwain
06-23-2017, 2:57 PM
Thanks all for the replies! I'll check out the sonic cable height sensor - that really does look like the right tool. I'll probably try the trig solution with the angle gauge too - looks like a good way to double check.

John, I really appreciate you taking the time to go out and try the laser to see if it would work on the power lines!! Your results are probably about what I expected - possible if you can get the laser to point right on the line. I've got a pair of those red glasses that help you spot a laser pointer, but I suspect that it would really have to be in the dark to see well enough to get a reading. We are mobilizing an excavator for a job site and will need to go under the lines 3-4 times. Really need something that is quick and easy to use in the day. But, you saved me a few bucks in trying something that might or might not work for our application. We are looking at transmission lines from 20-35' up.

Thanks again!

Matt Meiser
06-23-2017, 8:12 PM
Be careful shooting lasers into the sky. Pilots don't appreciate it and you might end up with visitors you don't want at your door.