HV power cables; safe distance

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On the Tamar cruising thread there's mention of being aware of the power cables. What is the recommended safe distance for an aluminium mast from these high tension power cables? Is there leccy engineer on these boards that can answer that?
 

sarabande

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9m safe working distance ?

Here the HSE take on working near power lines:-

http://www.hse.gov.uk/electricity/information/overhead.htm


For working on the farm we have to use this doc:-
http://www.hse.gov.uk/pubns/indg389.pdf

and from a Working safely in forests book, there is reference to a "Vicinity Zone" (which I learned as the Flashover Distance years ago)

Details
Up to and including 1 kV 1 m
Exceeding 1 kV but not exceeding 11 kV 2 m
Exceeding 11 kV but not exceeding 33 kV 2.5 m
Exceeding 33 kV but not exceeding 66 kV 3 m
Exceeding 66 kV but not exceeding 132 kV 3.5 m
Exceeding 132 kV but not exceeding 275 kV 4 m
Exceeding 275 kV but not exceeding 400 kV 5 m

Now these are for trees in the vicinity of power lines. With a mast (AND aerials) possibly having a higher electric potential than a tree, I'd look at increasing that distance by 50%.

Usual caveats apply, but I did see some pictures of fluorescent lights set up on the ground under the mains pylons, and they were lit up !


EDIT - found it ! Perhaps if the fluorescents on board light up, you are too close ?

tubes.jpg
 
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Beadle

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A few years ago I was driving past a large power station and heard funny noise from under car. I stopped and had a poke about under the car and every time I touched a metal bit I got a shock.

Couldn't work this out until I looked up and saw I had stopped directly under a 440kV line. Drove a few yards away and everything fine - no shocks at all.

I reckon that as it was a dry day the tyres were acting as insulators and the whole thing was acting as a capacitive voltage divider.

I assume the height of the lines meet all the regulations but there definitely is some interaction. I've never heard of any problems being caused by this, but all the same it would be good to make sure every thing is electrically earthed.
 

arfa

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I have heard about cyclists getting static build up when going under pylons and a shock when they touch the frame as they are unearthed until they put a foot on the ground. It has not happened to me personally though
 

Clyde_Wanderer

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I have heard about cyclists getting static build up when going under pylons and a shock when they touch the frame as they are unearthed until they put a foot on the ground. It has not happened to me personally though

Maybe a perfect time to allow swmbo to put her foot down, first.:D:D:D
 

sighmoon

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Well now, this is interesting. I had unquestioningly assumed that the height on the chart is the height of an object that can pass safely under it.

If the power lines are 16m above chart datum, and the mast is 17m from the water, this means I probably need a tide 8m or so below chart datum to squeeze through.
 
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BabySharkDooDooDooDooDoo

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Well now, this is interesting. I had unquestioningly assumed that the height on the chart is the height of an object that can pass safely under it.

If the power lines are 16m above chart datum, and the mast is 17m from the water, this means I probably need a tide 8m or so below chart datum to squeeze through.

I'd also assumed that the heights above HAT given on charts and pilot books for power cables were safe clearance distances rather than the physical height which would then require further calculations based on what you thought their voltage was :eek:
 

Rum_Pirate

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Not power cables but interesting

Cruise ship barely squeezes under bridge

November 01, 2010|By A. Pawlowski, CNN

Royal Caribbean's Allure of the Seas passes under Denmark's Storebaelt Bridge on Saturday.
It was a tight squeeze for a giant new cruise ship sailing from Europe to its home port in in Fort Lauderdale, Florida, over the weekend.

Royal Caribbean's Allure of the Seas passed under Denmark's Storebaelt Bridge with about a foot to spare, drawing applause from people on board the ship.

The captain called it "the great excitement of the day."

The normal height of the ship from the water level to the top is about 73 meters (240 feet), said Capt. Hernan Zini, but the vessel couldn't be higher than 65 meters (213 feet) in order to safely go under the bridge, the captain said.

To make that happen, the crew lowered the ship's retractable twin smokestacks, carefully adjusted the ballast so the ship wouldn't be too light (and therefore sitting too high in the water) and boosted its speed.

"When you increase the speed in relatively confined waters, the ship has a suction effect from the bottom, and that actually makes the ship go a bit deeper into the water," Zini said.

The plan went off without a hitch, and the ship safely cleared the bridge.

The vessel is the sister ship of the Oasis of the Seas. The pair are the largest cruise ships in the world.
 

machurley22

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Clearances shown on charts for any overhead object relate only to the physical height of the object. Apart from anything else the distance that can be bridged by a spark varies with atmospheric conditions. I presume that this height is also at a specified temperature (although I don't know what it is) since a long cable span will be very significantly affected by expansion and contraction.
 
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Plomong

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On the Tamar cruising thread there's mention of being aware of the power cables. What is the recommended safe distance for an aluminium mast from these high tension power cables? Is there leccy engineer on these boards that can answer that?

My old and dog-eared copy of Admiralty Publication 5011 (5th edition, 1984) says on page 10:
"Power transmission line, with safe overhead clearance (see note) and pylons".

The note says:
"The safe overhead clearance above HW, as defined by the responsible authority, is given (in magenta) where known; otherwise the physical vertical clearance is shown (in black, as in H18a)".

H18a is the symbology for telegraph or telephone lines.

I am quite certain that the Admiralty and the "responsible authority" woud make bl00dy sure that the value given was really safe -- HV is nothing to be played with, even 1 KV will kill, very permanently, and with sonic accompaniment.

So, all those saying subtract the length of the insulator strings + 50% or whatnot are being over cautious. The height as given in magenta is safe.

Plomong
 

bastonjock

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has anyone ever heard of a yacht that has been hit by a strike from HV?.There are a multitude of safety rules governing electrical distribution,ive witnessed in person a guy getting a 24000 amp burn,if it had not been so serious it would have been funny he was smoking like something out of a cartoon.Ive also seen a guy who had been hit by 33kv and survived,he was covered on scar tissue.An ordinary leccy will not know the answer to this,it would take an Electrical engineer who specialises in HV to know this one, but i put some faith in the guys who make up the rules as to having enough sense to put the power lines well out of the way of a yachts mast.The picure with the fluorescents was interesting,from memory theres a rule that restricts livestock from being near to the bottom of a pylon as the are a lot more vulnerable to the effects of electricity than we are.
 

sarabande

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if there is a rule about keeping livestock away from pylons, I am not aware of it. In fact, EDF seem to like sheep grazing right underneath, as it keeps the grass short for their maintenance crews, as otherwise they have to mow the grass.
 

[2574]

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has anyone ever heard of a yacht that has been hit by a strike from HV?

Yes, I know of a largish cat that suffered a strike from HV in the upper reaches of Portsmouth harbour. I don't know exactly where he was though I believe it was Fareham Channel. The electrics of the boat were completely shot, the mast was burned and parts of the boat melted. It was a proper mess. The boat was rebuilt at considerable cost.

rob
 

[2574]

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The note says:
"The safe overhead clearance above HW, as defined by the responsible authority, is given (in magenta) where known; otherwise the physical vertical clearance is shown (in black, as in H18a)".

Plomong

Thanks for that; it's a critical piece of information and to use a colour change is a rather subtle distinction between safe height and physical height. One to watch out for!

Rob
 

whipper_snapper

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Also, bear in mind that the distance given is the lowest point in the 'sag'. Depending on how the cable hangs and where its supports are, you can win many metres by not crossing at its middle point but by going as close to one support or the other (as navigational requirements permit!).
 

sailorman

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we had a delivery of DG units from Pilkingtons & the driver would not place the HIAB within 9m of cables. these units had to be off loaded in the road & carried.
The 9m distance is Co Rules
 

taz

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we had a delivery of DG units from Pilkingtons & the driver would not place the HIAB within 9m of cables. these units had to be off loaded in the road & carried.
The 9m distance is Co Rules

Same here, we couldn`t get deliveries of any building materials on site because of the 9m ruling. Seems to be pretty much the standard used, with HIAB/crane anyway.
 
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