How to measure the height of an overhead power line?

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tim0001

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#298694 7-Jul-2022 22:39

We are looking at building a shed in the general vicinity of overhead low voltage power lines, and therefore need to make sure that we met the safety regs. I've made a few estimates of the power line height using: trig, photos, phone apps etc. But I'm wondering whether there is a more "professional" approach.

The cables are bare and still shiny (about a year old), so I perhaps a cheap laser distance measure would work??? (mounted on a tripod in low light conditions.) The cable height is roughly 7m. I've never used a laser distance meter.....would it work?

thanks

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#2939473 7-Jul-2022 23:23

Aiming for the lines themselves with a laser meter would be very hard, but you should be able to hit a cross bar with the laser beam. I know that's not going to account for sag in the wires between poles, but that's your best bet if you want to try a laser meter. But, I'm intrigued: what's wrong with trig? Should be well and truly accurate enough for your purposes.

gregmcc

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#2939488 8-Jul-2022 05:25

You contact your local network company or approved contractor who will have the insulated tools to preform the the job safely.

Bung

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#2939491 8-Jul-2022 07:15

tim0001:
We are looking at building a shed in the general vicinity of overhead low voltage power lines, and therefore need to make sure that we met the safety regs.

The cable height is roughly 7m.

How ambitious is this shed going to be?

nztim

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#2939496 8-Jul-2022 08:08

have the power company do this

Any views expressed on these forums are my own and don't necessarily reflect those of my employer.

tim0001

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#2939558 8-Jul-2022 09:38

pih: But, I'm intrigued: what's wrong with trig? Should be well and truly accurate enough for your purposes.

Playing with lasers is always going to be more fun than trig. But yeah, trig is accurate enough in my opinion because we are not even close to the limits. According to NZECP34: 2001, "A specific engineering study must be carried out by a competent person, to establish actual distances in accordance with the requirements of Table 3". Thought laser measurements might make the study more credible.

We are 3 hours travel time from town, so getting a professional to complete the report could be expensive.

tim0001

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#2939559 8-Jul-2022 09:42

nztim:

have the power company do this

Given the travel time (3hrs) I'm worried that it might come with a large price tag.

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Danite

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#2939564 8-Jul-2022 09:52

Could buy a couple of pieces of 20/25mm conduit and push them together, would wobble but be safe.

Bung

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#2939566 8-Jul-2022 09:56

Are you going to be far enough from limits to use Table 2 distances?

johno1234

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#2939624 8-Jul-2022 10:24

If using trigonometry, won't you need to measure the angle to the wire with a theodolite (Or a protractor I guess) plus account for ground level changes? In simple terms... *if* the ground is level, stand under the wire then walk away perpendicular until it is at a 45 degree angle - then the height is the same as the distance walked.

tim0001

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#2939716 8-Jul-2022 11:45

Bung: Are you going to be far enough from limits to use Table 2 distances?

The height criteria is ok, but the horizontal distance is a fail (about 2.5 metres horizontally from the lines). The standard isn't super clear on whether its an AND or OR situation, but from what I've seen elsewhere both criteria must be met. Would be very happy to be told I'm wrong on that.

tim0001

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#2939721 8-Jul-2022 12:02

johno1234:

If using trigonometry, won't you need to measure the angle to the wire with a theodolite (Or a protractor I guess) plus account for ground level changes? In simple terms... *if* the ground is level, stand under the wire then walk away perpendicular until it is at a 45 degree angle - then the height is the same as the distance walked.

Sadly I don't have a theodolite. There's a couple of augmented reality phone apps I've been using to measure angles. Haven't fully checked calibration, but the angles seem fairly consistent between phones and apps. I've also placed a 2.5 meter pole under the line and taken a photo from a long distance.

I think my biggest challenge will be appearing to be "competent" when doing the "specific engineering study". The only thing I've got in my favour is a degree in electrical engineering.

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mdooher

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#2939746 8-Jul-2022 12:33

tim0001:

We are looking at building a shed in the general vicinity of overhead low voltage power lines, and therefore need to make sure that we met the safety regs. I've made a few estimates of the power line height using: trig, photos, phone apps etc. But I'm wondering whether there is a more "professional" approach.

The cables are bare and still shiny (about a year old), so I perhaps a cheap laser distance measure would work??? (mounted on a tripod in low light conditions.) The cable height is roughly 7m. I've never used a laser distance meter.....would it work?

thanks

is this your incoming overhead mains or are you talking about the network LV cables?

as far as measuring the height the network company will either use a measuring stick (well that's what we call it anyway) or a laser. The laser is quite cool because it will measure the closest thing to it over a pre-set angle so it stops you needing to aim so accurately

having said that that I've done it plenty of times with a standard laser measuring tool. (pick a calm day) eventually you get a reading

I may have even done it with a wind up type tape measure by just throwing it over the lines... (don't do that, it's stupid)

Matthew

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#2939757 8-Jul-2022 13:08

tim0001:
Bung: Are you going to be far enough from limits to use Table 2 distances?

The height criteria is ok, but the horizontal distance is a fail (about 2.5 metres horizontally from the lines). The standard isn't super clear on whether its an AND or OR situation, but from what I've seen elsewhere both criteria must be met. Would be very happy to be told I'm wrong on that.

I take it that the height criteria also applies the specified horizontal distance either side of the line. Maybe for clarity's sake you should attach a sketch showing how the shed will relate to the lines.

mdooher

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#2939761 8-Jul-2022 13:14

The reason I asked what type of line we are talking about is because the it depends on where the line is. I.e. does it from part of the installation (so ASNZS3000 applies) or is it network, because then its ECP54 and the distances are different

Matthew

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#2939770 8-Jul-2022 13:53

mdooher:

I may have even done it with a wind up type tape measure by just throwing it over the lines... (don't do that, it's stupid)

I was going to suggest throwing a weight attached to a length of nylon cord over the line and measuring, but despite not being able to see how this would be dangerous, it still doesn't seem a good idea.

I would have thought that, unless it's right on the edge of being allowable, the trig methods are accurate enough.

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