Will it really arc in this situation?

[Elecman]

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.

That is the Farady Cage effect, the metal of the car produces an equipotential zones around the vehicle in which the occupants are safe, they only get electrocuted if they step out of the vehicle and cause themselves to become the path to the general mass of the earth. You can see linesmen working on live grid electricity conductors because the cage they are in is separated from the earth potential and at the line potential ( up to 400 KV)

 

[tony_mac]

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.

There was certainly a much greater risk of falling.

But, I think someone climbing a stepladder on a platform, underneath wires, could get to the point where the danger of electrocution becomes something to worry about.
(And, given the foolhardy position of the ladder, I wouldn't like to assume that he didn't climb it any further)

 

[Phil.]

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.

As far as the electrickery is concerned he is perfectly safe. With a distance of some eight feet between himself and the nearest wire there is no chance of any arcing that far. The danger that he's in is falling off the ladder either by overbalancing or getting whacked off by the draught from a passing train.
--- old post above --- --- new post below ---

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?

Yes.
..........
--- old post above --- --- new post below ---

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!

Please read the posts. No-one is justifying using a ladder. Mounting a ladder like that on the edge of a platform is irresponsibly bonkers. The question was whether that if he was safe from an electrical arcing point of view and the answer is yes. At the height he's got himself to he's still way outside any arcing possibilities. His danger is falling off the ladder or being knocked off by a train's slipstream.
Just to get the height in perspective....The normal height of overheads through a station is 16'. A platform is 3' 6". Put a six foot person two feet in the air on a ladder and that person's head is still lower than the roof of a passenger train. Just remember also that he's not directly underneath the contact wire so he's actually further away than the distance that I've calculated. He's probably more like seven feet away from the contact wire.

 

[Llanigraham]

try reading post #18

I have and it is incorrect.
There are several excellent videos available supporting that.

 

[najaB]

I have and it is incorrect.
There are several excellent videos available supporting that.

I'm not sure that it is wrong. It certainly matches my understanding - people are safe from lightning inside a car because the body acts as a Faraday cage and the tires conduct the charge to ground.

 

[edwin_m]

The reason people in a vehicle are relatively safe from high voltages is that the vehicle metalwork provides a better path to earth so most of the current will flow through it instead of through anyone inside.

I expect the tyres would conduct if subject to 25kV, and if they didn't the ground clearance of the vehicle would probably be small enough to arc to the road beneath it. Anybody getting in or out of the vehicle while the current was flowing would be in danger as they might provide a reasonably good conductive path to earth so a substantial part of the current might flow through them.

Railway 25kV is protected by fast circuit breakers so will not flow through a fault for more than a very short time. However, as mentioned somewhere further back, it may be re-energised to check there is a persistent fault before investigating further, and that could coincide with someone getting out of a vehicle. So I'm not sure what the advice would be if trapped in a vehicle on a level crossing with the OLE down on top of it!

 

[LexyBoy]

^ What Phil said. Unless he whipped out a selfie stick and waved it at the OLE, there's no danger of being electrocuted (but a very high danger of being killed falling onto the track, even without trains getting involved).

Think about the insulators used. They're what, a foot or so long? And that's enough to insulate from 25 kV, even when they are soaking with rain. You'd need to get within inches of the conductor to arc in dry air as pictured.

Of course the regulations require much bigger clearances - that's because people make mistakes or misjudgements. If the outcome is probable death, then you make damn sure that even if someone really cocks it up, they're still in one piece for their boss to give them an earbashing.

It *could* arc.
[snip image]
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.

If it were "the exact opposite" then you'd expect to see constant arcing to all the bodywork which is above the orange line.

 

[Tio Terry]

Safe working practices around High Voltage lines and equipment is defined in BS EN 50122.

Reading some of the comments above it seems it would be a good idea for people to read it!

 

[QueensCurve]

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.

There is not, at the time that image was taken, an immediate risk of arcing affecting the person on the ladder.

The picture appears to put the person's head almost in line with the lnsulator on the lower cantilever arm of the OHLE. Bear in mind in a fall it may be instinctive to grab something for safety. He could have grabbed the live arm.

While the higher risk may involve being hit by the moving train, it is possible, in the event of falling, that someone might have come into contact with the live footprint of the OHLE.

As such, the situation appears electrically unsafe as well as mechanically.

See graphic consequences of grabbing the live 25kV OHLE.

 

[Deepgreen]

Here's a scenario. A platform end crowded with photographers/viewers and someone arriving with a, say, 5'6" foot high metal ladder (including top handrails). That person is 6' 8" (not that rare). Owing to the crowding, the ladder-bearer lifts it over his head to avoid knocking other people, into his selected spot. His arms add 2'6" to the height, and we have 5'6"+6'8"+2'6" = 14'10". Even allowing for the horizontal distance to the wires, I would guess that that is not far from being capable of inducing arcing.

 

[Phil.]

Ah, I wonder how long it would take before the thread wandered from the actuality to the "what if".

 

[KTHV]

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.

Top Gear did a very good feature on cars and electrical charges a while ago

https://www.youtube.com/watch?v=ve6XGKZxYxA

 

[cjmillsnun]

Safe working practices around High Voltage lines and equipment is defined in BS EN 50122.

Reading some of the comments above it seems it would be a good idea for people to read it!

Where is the like button. Someone who is actually referring to laid down safety standards.

 

[najaB]

Ah, I wonder how long it would take before the thread wandered from the actuality to the "what if".

The only difference between the 'actual' and the 'possible' is probability. At the exact instant that the photo was taken he wasn't in any real danger of being electrocuted - I think we're all agreed on that. Before and after, well that's another story.

 

[GB]

As far as the electrickery is concerned he is perfectly safe. With a distance of some eight feet between himself and the nearest wire there is no chance of any arcing that far. The danger that he's in is falling off the ladder either by overbalancing or getting whacked off by the draught from a passing train.
--- old post above --- --- new post below ---


Yes.
..........
--- old post above --- --- new post below ---


Please read the posts. No-one is justifying using a ladder. Mounting a ladder like that on the edge of a platform is irresponsibly bonkers. The question was whether that if he was safe from an electrical arcing point of view and the answer is yes. At the height he's got himself to he's still way outside any arcing possibilities. His danger is falling off the ladder or being knocked off by a train's slipstream.
Just to get the height in perspective....The normal height of overheads through a station is 16'. A platform is 3' 6". Put a six foot person two feet in the air on a ladder and that person's head is still lower than the roof of a passenger train. Just remember also that he's not directly underneath the contact wire so he's actually further away than the distance that I've calculated. He's probably more like seven feet away from the contact wire.

Thats great. But the safe distance from live OLE is 9 feet.

The issue is also one of behavioral traits. He clearly has no common sense so whats to stop him climbing another couple of rungs to get that perfect shot?
--- old post above --- --- new post below ---

Ah, I wonder how long it would take before the thread wandered from the actuality to the "what if".

....and how do you think the rules of today came about? Or is something only dangerous if it does actually result in injury/death?

 

[tony_mac]

Ah, I wonder how long it would take before the thread wandered from the actuality to the "what if".

The whole thread is based around "what if" - we know that he wasn't actually electrocuted.
The original question was implying that he would have been perfectly safe, no matter what he did with his ladder; I think it is worth challenging that implication.

 

[Phil.]

The whole thread is based around "what if" - we know that he wasn't actually electrocuted.
The original question was implying that he would have been perfectly safe, no matter what he did with his ladder; I think it is worth challenging that implication.

The original question - I've just re-read it - is implying that from an electrical point was he safe? The answer - from an electrical point - is yes, he is perfectly safe.
It was "Deepgreen" that introduced the "what if" scenario of a 6' 8" bloke carrying and lifting a 5' 6" ladder. No-one was talking about such a situation, the discussion was about the fool with the ladder at Newton-le-Willows.

 

[Deepgreen]

The original question - I've just re-read it - is implying that from an electrical point was he safe? The answer - from an electrical point - is yes, he is perfectly safe.
It was "Deepgreen" that introduced the "what if" scenario of a 6' 8" bloke carrying and lifting a 5' 6" ladder. No-one was talking about such a situation, the discussion was about the fool with the ladder at Newton-le-Willows.

Indeed, fair enough, but I think the original question naturally leads onto plausible 'what-if' scenarios, as the electrical safety of the person at NLW can only be judged from the moment caught in the photo. I don't it's too much of a deviation to consider the implications of similar, but 'enhanced' scenarios.

 

[LexyBoy]

Safe working practices around High Voltage lines and equipment is defined in BS EN 50122.

Reading some of the comments above it seems it would be a good idea for people to read it!

As discussed above, I think there's different interpretations of the question:
(a) was there a chance of arcing to the bloke as seen in the picture - as per the thread title (answer- no, he's way too far away), or,
(b) was he putting himself at risk of electrocution (answer- yes, by putting himself closer to the wires and carrying a long metal conductor about).

 

[Tio Terry]

As discussed above, I think there's different interpretations of the question:
(a) was there a chance of arcing to the bloke as seen in the picture - as per the thread title (answer- no, he's way too far away), or,
(b) was he putting himself at risk of electrocution (answer- yes, by putting himself closer to the wires and carrying a long metal conductor about).

Too far away? How away from the end of a passing pantograph horn would he be if a train were to pass through the station?

The clearances given in EN 50122 are for a reason, they include a tolerance factor for the variables such a damp weather.

The ORR are now insisting a clearance between an average height person standing behind the yellow line to the closest unprotected live part (usually the end of the pantograph) of 3.5M - as required by EN50122. Less than that and you need to undertake an Explicit Risk Estimation (ERE) which is very likely to show that "obstacles" need to be placed such that the possibility of coming too close to the exposed live parts is minimised. In the ERE you need to consider things like selfie sticks, helium balloons, umbrellas etc., but I doubt anyone would consider a member of the public bringing a ladder to the station and climbing it!

 

[tony_mac]

The original question - I've just re-read it - is implying that from an electrical point was he safe?

There was slightly more to it - it implies that there was a safety cushion of at least 8 feet (as the line is at least 12 feet away, and lorries can pass safely within 4 feet). This would imply that whatever he did with the ladder he would still be perfectly safe.

While not disputing that 2 feet up a ladder isn't a problem, I still think it's worth mentioning that there may not really be such a big margin for error, and that arseing about with a stepladder on a platform could be a cause for concern.

 

[Flying_Turtle]

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.

1 mm or 1cm?

 

[DaleCooper]

1 mm or 1cm?

Wikipedia gives the dielectric strength of air as 3MV/m (or 3kV/mm) but under real life conditions that is reduced by water vapour in the air, shape of the electrodes and other factors so 1kV/mm is probably a good guide figure.

 

[najaB]

Wikipedia gives the dielectric strength of air as 3MV/m (or 3kV/mm) but under real life conditions that is reduced by water vapour in the air, shape of the electrodes and other factors so 1kV/mm is probably a good guide figure.

The thing to remember though is that the breakdown voltage is affected by a *lot* of factors. 1kV/mm is a fair approximation for parallel flat surfaces, throw something pointy in there and the safe distance might be significantly greater.

 

[thenorthern]

Its not clear from the picture but did the man have a tripod?

 

[PermitToTravel]

There was slightly more to it - it implies that there was a safety cushion of at least 8 feet (as the line is at least 12 feet away, and lorries can pass safely within 4 feet). This would imply that whatever he did with the ladder he would still be perfectly safe.

I wouldn't go that far - do we reckon he carried it onto the platform safely, or will he have been waving it about? He hasn't demonstrated much common sense :P

Wikipedia gives the dielectric strength of air as 3MV/m (or 3kV/mm) but under real life conditions that is reduced by water vapour in the air, shape of the electrodes and other factors so 1kV/mm is probably a good guide figure.

Dielectric strength is the inverse quantity, so by that figure electricity should be able to travel a third of a millimetre per kilovolt. In practice 1mm/kV is definitely possible - the difference is probably made up by the parallel conductances of different routes through the air.

 

[edwin_m]

Is there also an issue with induced current from the fields around the 25kV affecting the human body, for example problems with muscle control or pacemakers? This might explain why the minimum separation for people is so much more than the minimum separation for inanimate objects.

 

[LexyBoy]

Too far away? How away from the end of a passing pantograph horn would he be if a train were to pass through the station?

Certainly no closer than the top of the train the pantograph's attached to! And most likely rapidly moving in an earthwards direction, given how close to the platform edge he is.

 

[LesS]

The real issue here is the guy on the ladder placed next to the platform edge. Any loss of balance would see him on the tracks. The photographers have their backs to oncoming trains. A fast train would be on top of them before they knew it was there. I have had this experience even when I knew a train was due and was well within the yellow line.

There is no danger from arcing for all of the reasons given above. Here in Sydney the rooves of our EMU's are only a few inches from the contact wire (1500v DC).

On the issue of general safety, we had a heritage electric tour on some of our suburban lines today and the photographers were out in force. Station staff were alert to keep even tripod legs amongst other things within the yellow line. The remotely controlled security cameras are able to zoom in and out and these were being closely monitored.

 

[Phil.]

We're going around in circles now.