Telegraph Poles - How Much Clearance?

[Little Rascal]

I was just musing over sailing a dinghy on my local river (the Nene)...

There are some telegraph wires crossing the river at about 30 feet - I don't know what they carry, but if it were electricity:

How much clearance would you need? Can sparks jump and if so how far?

 

[Champagne Murphy]

Is this leading to a Les Dawson style mother-in-law gag?

 

[VicS]

I was just musing over sailing a dinghy on my local river (the Nene)...

There are some telegraph wires crossing the river at about 30 feet - I don't know what they carry, but if it were electricity:

How much clearance would you need? Can sparks jump and if so how far?

Yep High voltages can jump a good distance but depends on the voltage. If you have a chart the figure given is the safe clearance .

Telegraph wires dont carry high voltages

 

[awol]

I was just musing over sailing a dinghy on my local river (the Nene)...

There are some telegraph wires crossing the river at about 30 feet - I don't know what they carry, but if it were electricity:

How much clearance would you need? Can sparks jump and if so how far?

Rated maximum 3 phase a.c. line voltage (a.c. line to earth voltage)
Basic safety clearance

High Voltage not exceeding 11kV (6.35kV) 500mm
Exceeding 11kV (6.35kV) not exceeding 33kV (19.0kV) 500mm
Exceeding 33kV (19.0kV) but not exceeding 44kV (25.4kV) 600mm
Exceeding 44kV (25.4kV) but not exceeding 66kV (38.0kV) 700mm

You could always use a wooden mast.

 

[Spyro]

There are minimum clearances where they cross roads not sure what they are. 5.5 m and 6.5m seems to ring a bell ( no pun) depending on what class of road but 30ft is way over the limit. They do carry electricity but it wont kill you. Usual for a normar telephone line is around 50v dc, ISDN is 90v dc but you could get up to 120v dc depending on what type of service they are carrying. You could get a tingle off one if some one was ringing on the line at the same time you were touching them. Ringing current is AC.

 

[Spyro]

Rated maximum 3 phase a.c. line voltage (a.c. line to earth voltage)
Basic safety clearance

High Voltage not exceeding 11kV (6.35kV) 500mm
Exceeding 11kV (6.35kV) not exceeding 33kV (19.0kV) 500mm
Exceeding 33kV (19.0kV) but not exceeding 44kV (25.4kV) 600mm
Exceeding 44kV (25.4kV) but not exceeding 66kV (38.0kV) 700mm

You could always use a wooden mast.

Think you need a few more zeros there

 

[VicS]

This site may answer the questions

http://www.hse.gov.uk/pubns/indg389.pdf

 

[awol]

Think you need a few more zeros there

Not according to the Railtrack Document GM/RT1040 "Safe Working On or Near Electrical Equipment". Mind you, it was withdrawn in April 2009.

Wait a minute, I'm giving actual references for my spurious answers to questions on the S'butt forum. That must be against the rules, surely?

 

[Plomong]

Telegraph wires dont carry high voltages

Some do -- those telephone cables that also carry power to inline repeaters can give a nasty shock to anyone cutting them, but nothing like what an electricity supply line of any normal voltage would give. The impedance back to source is much higher and the ability of the power source to push big amps your way is much lower, but still dangerous, none-the-less.

In my cable-minding days, long, long ago, I remember some underground lines with over 1200 V on them.

Plomong

 

[Little Rascal]

Hmm, thanks guys... food for thought.

No charts for 30 miles up the Nene Vic! There are so many other height restrictions, bridges, guillotine locks at about 8ft that no other water users (ie Cabin Cruisers) are very interested and there isn't a clearance guage or even a warning sign (Environment Agency look after that sort of thing). But for me (or Dylan - he's been up here) - who drop and raise the mast willy nilly...

30ft was just a guess based on the height of a person from a hundred yards or so. The mast will probably be less than 18ft (Heron dinghy?) and wooden gunter so I'll probably be fine.

Just thought it was worth finding out as there are several that cross the Nene... some lower than others.

Thanks,
LR

 

[Spyro]

Not according to the Railtrack Document GM/RT1040 "Safe Working On or Near Electrical Equipment". Mind you, it was withdrawn in April 2009.

Wait a minute, I'm giving actual references for my spurious answers to questions on the S'butt forum. That must be against the rules, surely?

Are you sure that is not depth underground?

 

[Spyro]

Some do -- those telephone cables that also carry power to inline repeaters can give a nasty shock to anyone cutting them, but nothing like what an electricity supply line of any normal voltage would give. The impedance back to source is much higher and the ability of the power source to push big amps your way is much lower, but still dangerous, none-the-less.

In my cable-minding days, long, long ago, I remember some underground lines with over 1200 V on them.

Plomong

Never seen overhead cables doing that. Now if you are talking subsea cables they will kill you. Unless it's fibre.

 

[dylanwinter]

the nene

I took the slug up the nene

had a wonderful time

mast only about 20 foot above thge water

I dropped the mast for every bridge and cable

films on the website

D

 

[Little Rascal]

Cheers Dylan. And they are very good films!

There is one great stretch between one of the cruising club yards and Waternewton Mill where the wind seems to always let you reach both ways... Just that there is this telegrah wire half way down

Of course I could drop the mast for a single transit but the idea is to keep the boat at the yard and use that reach for evening sailing on the river.

30ft high - 16-18ft wooden masted Heron dinghy : would you try it?

Cant be any worse than death by Fray Bentos detonation...


Jon

 

[VicS]

Hmm, thanks guys... food for thought.

No charts for 30 miles up the Nene Vic! There are so many other height restrictions, bridges, guillotine locks at about 8ft that no other water users (ie Cabin Cruisers) are very interested and there isn't a clearance guage or even a warning sign (Environment Agency look after that sort of thing). But for me (or Dylan - he's been up here) - who drop and raise the mast willy nilly...

30ft was just a guess based on the height of a person from a hundred yards or so. The mast will probably be less than 18ft (Heron dinghy?) and wooden gunter so I'll probably be fine.

Just thought it was worth finding out as there are several that cross the Nene... some lower than others.

Thanks,
LR

I guessed you probably meant way up river or i'd have posted a link to the charts that cover the bit from Wisbech to the Wash. The cables along there have 30 m safe clearance! Just about get a Heron under them or a small ship!

I found some other figures that say Safe distances for working near Hv cables and equipment

750v to 75 kv 3 metres
75kv to 250kv 4.5 metres
250 kv to 550kv 6metres

Also for driving under: 2m, 3 m and 4m respectively for the above voltage ranges

I also found the Railtrack document to which awol refers. He's not making it up!

Not wide enough for sailing is it 30 miles upstream. A canoe would be more suitable

 

[dylanwinter]

sailing

I guessed you probably meant way up river or i'd have posted a link to the charts that cover the bit from Wisbech to the Wash. The cables along there have 30 m safe clearance! Just about get a Heron under them or a small ship!

I found some other figures that say Safe distances for working near Hv cables and equipment

750v to 75 kv 3 metres
75kv to 250kv 4.5 metres
250 kv to 550kv 6metres

Also for driving under: 2m, 3 m and 4m respectively for the above voltage ranges

I also found the Railtrack document to which awol refers. He's not making it up!

Not wide enough for sailing is it 30 miles upstream. A canoe would be more suitable

wide enugh for sailing

but not wide enough for beatin

still lots of great sailing to be done

d

 

[Little Rascal]

A canoe would be more suitable

Got two of them already... one of which is wasted on the river anyway

It's wider than whole chunks of the Broads! There were dinghy and keelboat races on the Nene at Peterborough until they petered out in the 70's (before my time).

Then nothing until Dylan came along....



Thanks for that HSE doc Vic: they look like the 33/11kV type. If minimum clearance is 5.2 m on the bank I should be ok on the river...

I could always get a steel tape measure

 

[Deleted member 36384]

I am ignorant when it comes to power or telephone lines but I always assumed that they had insulation covering a conducting core. I guess thats not the case and they are just bare wires?

 

[st599]

Think you need a few more zeros there

I think you've used the wrong units - should be cm not mm. Clearance upto 11 kV is approx 5m.

 

[bbg]

On an early thread someone made the point that wherever cables are supported by a tower, they are attached with insulators. It is pretty fair to assume that a spark won't jump a greater distance than the length of the insulator.

Don't know if that is right or not, but it seems logical to me.