Will it really arc in this situation?

[mac]

While I agree he is to close to the edge could someone explain to someone who knows nothing how he going to touch the wires and how the electric is going to jump across. He is 8 foot high at the most lorries go under them and they are 16 foot so the wires must be 20 foot high, if so that means he's at least 12 foot away so safe. If not how there must be thousands of lorries getting shocks from the wires every day.as there only 4 foot away.

Mod note - incident referred to in this thread.

Please stick to the technical aspects in this thread. This is not a discussion on whether such actions are stupid, as this had pretty much been established in the earlier thread.

 

[PermitToTravel]

While I agree he is to close to the edge could someone explain to someone who knows nothing how he going to touch the wires and how the electric is going to jump across. He is 8 foot high at the most lorries go under them and they are 16 foot so the wires must be 20 foot high, if so that means he's at least 12 foot away so safe. If not how there must be thousands of lorries getting shocks from the wires every day.as there only 4 foot away.

The lorries are earthed via rubber tyres. The idiot was earthed via a metal ladder. Metal is better at conducting electricity than rubber.

That said, it's unlikely that there would have been an electrical arc. A good rule of thumb for the distance that electricity will jump in dry air is about 1mm per kV, which would need one to get very very close indeed to an overhead line before electrocution became likely. The main risks, in the weather pictured, would be a passing train startling him into losing his balance, or the wind from a passing train pulling him beneath it.

 

[mac]

The lorries are earthed via rubber tyres. The idiot was earthed via a metal ladder. Metal is better at conducting electricity than rubber.

That said, it's unlikely that there would have been an electrical arc. A good rule of thumb for the distance that electricity will jump in dry air is about 1mm per kV, which would need one to get very very close indeed to an overhead line before electrocution became likely. The main risks, in the weather pictured, would be a passing train startling him into losing his balance, or the wind from a passing train pulling him beneath it.

So basically apart from falling off he's safe, or in other words 8 of these 10 pages are wrong

 

[tony_mac]

The wire may be 15-16 foot high (http://www.rmweb.co.uk/community/index.php?/topic/71391-british-railways-ole-part-one-plain-track/)

The platform, 3-4 foot high
Add a person's height to a 5-foot step-ladder and you are getting dangerously close.
But, what's the point - are you trying to say that it's perfectly safe, or just arguing for the sake of it?

 

[mac]

The wire may be 15-16 foot high (http://www.rmweb.co.uk/community/index.php?/topic/71391-british-railways-ole-part-one-plain-track/)

The platform, 3-4 foot high
Add a person's height to a 5-foot step-ladder and you are getting dangerously close.
But, what's the point - are you trying to say that it's perfectly safe, or just arguing for the sake of it?

Just trying to get an answer to something I no nothing about. He was not on a 5 foot ladder he was only up 2 foot so not really any difference to all the others around him. You say about dangerously close what is close he was at least 12 foot away how far should he be compared to lorries going under them without arcing across to there metal trailers.

 

[snowball]

lorries go under them and they are 16 foot so the wires must be 20 foot high

They are higher at level crossings than elsewhere.

 

[Llanigraham]

The lorries are earthed via rubber tyres. The idiot was earthed via a metal ladder. Metal is better at conducting electricity than rubber.

That said, it's unlikely that there would have been an electrical arc. A good rule of thumb for the distance that electricity will jump in dry air is about 1mm per kV, which would need one to get very very close indeed to an overhead line before electrocution became likely. The main risks, in the weather pictured, would be a passing train startling him into losing his balance, or the wind from a passing train pulling him beneath it.

No they aren't, they are INSULATED!

 

[GB]

Rubber tyres are not always enough to insulate a vehicle from the OLE.

I remember a few years ago at Ely a lorry made contact with the OLE via its radio antenna which resulted in the tyres blowing which then blew the signalling system. Caused mayhem.

 

[mac]

No they aren't, they are INSULATED!

What is insulated on a curtain sided trailer with a metal roof?

 

[gimmea50anyday]

He was not on a 5 foot ladder he was only up 2 foot so not really any difference to all the others around him. You say about dangerously close....

I cannot believe some of the comments I am reading on here trying to justify the use of a ladder on an active railway line with OHLE only 2 foot away from a running line on which I pass through at over 70mph!

Is this guy for real? How can anyone justify using a ladder on any railway station platform, let alone one open for public use in the location he is using it. 5ft, 2ft, 6in doesnt make any difference how big the ladder so lets not split hairs here. That guy should not be there with that, end of. anyone who thinks behaving in this manner is justifiable had better reconsider what they choose to be their hobby, before they end up a 1/2 mile long smudge of peanut butter and jam along the railway line. And I sincerely hope its not my train that acts as the butter knife!

 

[mac]

I cannot believe some of the comments I am reading on here trying to justify the use of a ladder on an active railway line with OHLE only 2 foot away from a running line on which I pass through at over 70mph!

Is this guy for real? How can anyone justify using a ladder on any railway station platform, let alone one open for public use in the location he is using it. 5ft, 2ft, 6in doesnt make any difference how big the ladder so lets not split hairs here. That guy should not be there with that, end of. anyone who thinks behaving in this manner is justifiable had better reconsider what they choose to be their hobby, before they end up a 1/2 mile long smudge of peanut butter and jam along the railway line. And I sincerely hope its not my train that acts as the butter knife!

If you read my first post you will see I agree with you about taking a ladder onto the platform, my comments are about the questions I have asked and the answers to them concerning the overhead wires as I don't understand how someone can electrocute themselves and others around them from 12 foot away but lorries can go under wires with only 4 foot clearance.

 

[Kentish Paul]

Why should this be put to bed as soon as someone who knows nothing asks the ones in the no, as often happens when everyone agrees threads run on and on but as soon as someone asks something that doesn't fit the thread needs locking

Sorry, what are you on about?

By the way, in this context no is spelt know.

 

[mac]

Mods, can we put this to bed. All of us know the guy was a complete **** and should be dealt with.
All the posts about distances from OHLE and height above platform and rungs on ladder are irrelivant.

I'm on about your above post

 

[gimmea50anyday]

If you read my first post you will see I agree with you about taking a ladder onto the platform, my comments are about the questions I have asked and the answers to them concerning the overhead wires as I don't understand how someone can electrocute themselves and others around them from 12 foot away but lorries can go under wires with only 4 foot clearance.

I should reword that. That wasnt aimed at you was meant as a generalisation. Wasnt meant to single you out . Sorry.

 

[AlterEgo]

What is insulated on a curtain sided trailer with a metal roof?

He was speaking about the tyres....they do not Earth the vehicle, as rubber is an insulator.

 

[EM2]

It *could* arc.

Look at this Meridian. See the thin orange line, running across above the windscreen and just below the roof line? That is the 'safe' distance from OHLE. Below that line, it is very, very unlikely to arc. Above it, it is the exact opposite.

 

[gimmea50anyday]

Rubber tyres contain a significant amount of metal tho as used for strengthening and shape retention

A point worth making. If you are 5ft and standing on a 5ft ladder, that increases your height to 10ft. Now that is still clear of the 16ft6 height but its also significantly closer. The OHLE isnt at a fixed height and can vary by a significant amount. 16ft6 might be the safe height at a road level crossing but that doesnt mean the catenery is always at that height and can drop significantly to pass under say a bridge. Can you guarantee that 10ft is still safe?

 

[AndrewE]

He was speaking about the tyres....they do not Earth the vehicle, as rubber is an insulator.

...except that most vehicle tyres here are filled with carbon black, an electrical conductor.
This came to light a few decades ago when people were getting static shocks off new cars built in the far east, where rubber was cheaper than the carbon black, so the tyres were insulators! The solution was to fit Europe-made tyres!

 

[najaB]

The other thing to bear in mind is that, once started, an arc will quite happily continue through a much larger distance as the ionised air acts as a conductor.

So all it takes while you're up on the ladder, much closer to the OHLE, is for a random conductive object to blow past and start the current flowing and... well, your widow might be able to sell the ladder on eBay.

 

[kwerty]

You or anything you are in contact with (ladder, tools etc. ) must keep over 2.75m away from live parts of the OLE. Not entirely sure but from the picture I reckon he probably had a fair safety margin from the wires and was unlikely to be at risk from the OLE whilst standing on the ladder. But picking it up and carrying it along the platform it may have been possible to lift it within 2.75m of the wires.

 

[AndrewE]

It *could* arc.
[url]http://www.uraken.net/world/wrail/eng/class222/[/url]. Above it, it is the exact opposite.[/QUOTE]
I think you mean "Above it, it gets more likely the closer you approach it." Lots of factors involved, like how well you are earthed for a start, even atmospheric humidity.

 

[PaxVobiscum]

This Network Rail Guide to Overhead Electrification may be of interest to those without specialist knowledge, Section 12 (p.32 ff) in particular.

On the subject of tripods and the like, I have a monopod which extends to over 2m with which I am fairly confident I could actually touch live parts of the OHLE in some stations I've been in, not that would I wish to do so, of course.

But I have seen idiots waving tripods in the air above their heads while trying to adjust the length of their (ie the tripod's ) legs, apparently oblivious to the risk.

 

[tony_mac]

I don't understand how someone can electrocute themselves and others around them from 12 foot away but lorries can go under wires with only 4 foot clearance.

it's often somewhere near 12 feet from the platform height to the wire height. A person's head on a step ladder will obviously be very much closer - and quite possibly closer than 4ft.

Wires are also higher over level crossings.

 

[Llanigraham]

What is insulated on a curtain sided trailer with a metal roof?

The whole vehicle because it is on RUBBER tyres!

 

[DaveNewcastle]

Rubber tyres contain a significant amount of metal tho as used for strengthening and shape retention?

Yes. And they also get wet. And smeared with other contaminants - many conductive, where their conductivity can be enhanced by a wetted surface to ground.

 

[AndrewE]

The whole vehicle because it is on RUBBER tyres!

try reading post #18

 

[thenorthern]

With lorries and other mechanically propelled vehicles I think that if they do get caught in power lines the occupants are most of the time safe as long as they stay in the vehicle. Its not uncommon for cars to get struck by lighting and most of the time the car is undamaged. Most fatalities in these cases happen when people step out the vehicle and close the door behind them.

I don't think it would be likely that this man on the step ladder could be electrocuted but standing on what looks like its grounded aluminum ladder which itself its a very good conductor near to 25Kv AC cables isn't a good idea.

 

[PermitToTravel]

The whole vehicle because it is on RUBBER tyres!

If that were true you'd be able to safely stand on the roof of a lorry under OLE. Hint: you can't.

Rubber doesn't conduct as well as metal, and at domestic voltages, it's practically an insulator. At 25kV, most things will conduct (and that's ignoring that modern vehicle tyres are designed to conduct lightning strikes)

 

[3141]

I think the OP Mac asked a completely reasonable question, and among the following posters there were some who provided a reasoned answer. The person in question at Newton le Willows was undoubtedly foolish, but he wasn't far up his ladder, he wasn't directly under the wires, and the real risk was falling off the edge of the platform, not electrocution.

 

[PermitToTravel]

Unless he could fall onto the wire and stretch it towards a stanchion?