Lightning.

[EdwardCurrent]

Hello All,
I was wondering how, and if scaffolders have some sort of lightning protection to fix to their scaffolds ? And when a building is 'going up' with steelwork exposed at the highest point ?

Even if there is no 'earth path' , are measures in place to ensure workers safety ???

Thanks for any help,

Ed.
High voltage doing what is does !
http://www.koreus.com/video/arc_electrique.html

 

[breezer]

they do, its called chance.

 

[EdwardCurrent]

Breezer,

I am not trying to be picky but if the building was earthed by the electrical contractors wouldn't there be a possibility of harm if working on the scaffold ???

I am a bit confused here, sorry.

Thanks
Ed.

ps And as for tower crane operators, they would have thier own lightning conductor fitted ????

 

[breezer]

i am not saying you are being picky.

the building wont be earthed by the electrical contractors, becuse it is still being built, and they only bond the steel work if required, anyway

is your house earthed? no.

as for crane operators what do you suppse the crane is, if its not a giant ligtning conductor?

a lightning conductor is a copper strip that goes along the highest points and at intervals has "spikes"

I have been on tall buildings and when i first saw it was midly surprused, but the ligning conductor runs everywhere along the perimiter (preumably becuse no one knows where / if it will strike

the other end is connected to a giant earth rod.

 

[Steve]

I school i went to had lightening strips around all the perimeters and a rod at each corner Most of it was only single storey too.

 

[EdwardCurrent]

Hello Again,

Sorry for the delay but still puzzled here. I understand that it is not exactly DIY stuff but would like some help please.

How do you manage to keep the scaffold, steelwork and crane at the same potential ??


http://i171.photobucket.com/albums/u315/exwomble/DSC00182.jpg


Or have I got it wrong somewhere ?

Thanks for any help.

Ed.

 

[TicklyT]

If you are on scaffolding during a lightning strike, you are probably in about the same position as a bird perched on a HT cable. (Lots of volts in the cable, but no circuit, so nowhere for it to go)

However, if you complete a circuit (touching, say, scaffold and steelwork at the same time as the lightning strike), THEN there will be lots of Amps!

Can the scaffolding (or crane driver's cab) be considered as a faraday cage?

 

[bernardgreen]

Can the scaffolding (or crane driver's cab) be considered as a faraday cage?

Some are designed to be a Faraday cage. But then the chances are the crane will collapse as a result of the strike.

There are different opinions about lightning conductors.

One is the pointed ends spray electrons ( basic physics ) into the atmosphere to neutralise the build up of positive charge thus reducing the chance of a strike. ( but would not work if a negative charge on the cloud )

Another is the conductor vapourises and provides a plasma path for the main body of the strike. What gauge of copper in needed for safely carrying 30 thousand amps ?

 

[NamelessRob]

However, if you complete a circuit (touching, say, scaffold and steelwork at the same time as the lightning strike), THEN there will be lots of Amps

If the resistance to ground is lower straight through the scaffold than it is through a human body and a steel building, in theory you should be ok. (Though I'm not volunteering to test it)

If you are on scaffolding during a lightning strike, you are

...just asking for trouble?

 

[bernardgreen]

Problem with the current in a lightning strike is it has a very fast rise time and as such doesn't like conductors with bends in them. ( they have inductance which for changing currents is similar in effect to resistance ). So it will arc of a bend if there is another route to earth near by.

 

[Steve]

Another is the conductor vapourises and provides a plasma path for the main body of the strike. What gauge of copper in needed for safely carrying 30 thousand amps ?

2500mm²

 

[Taylortwocities]

What installation method would that be then? And what about if its run in thermal insulation?

 

[tim west]

Another is the conductor vapourises and provides a plasma path for the main body of the strike. What gauge of copper in needed for safely carrying 30 thousand amps ?

2500mm²

without insulation and clipped direct? Thats like a busbar that size is much bigger than necessary

 

[viewer]

Some years ago I was leaning on a wire fence watching the lightning / storm which appeared some distance away. Suddenly I was on my back several feet from the fence. Obviously I'd not been struck, but wasn't sure what had happened. At the time an electrical engineer friend suggested a current had been induced in the fence. What is pertinent to the above is that the fence was of the wires between metal uprights type. Every upright should have provided an earth, but they didn't. There are also well reported cases of aircraft / gliders being destroyed (definately not earthed!). Chances of being hit by lightning are greater than winning the big prize on the national lottery.
All in all, I'd keep off scaffolding during an electrical storm.

 

[Spark123]

I think the engineer is probably right, have you seen the experiment where they put a load of fluorescent tubes into the ground under pylons?As a fence will be acting like long pickup in parallel to the ground 'd have though it is quite possible that it can have a higher potential than that of the ground.
The other option is that the fence is infact in contact with the ground and a lightening strike nearby caused a pool of potential which had been picked up by the fence, you stood further downline at a different potential. That could hurt!!
They reckon the safest place to be in a lightening strike is in your car, knowing my luck if it got struck I'd crash .
Seriously though, if you are inside any metal cage (faraday cage) or surrounded by metal then you will be pretty well protected from potentials outside.