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Road resurfacing

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Re: Road resurfacing

I've always thought that DC holds you and AC throws you off.
Can't say as I've held onto anything at around mains voltage long enough to test the theory Huh

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Infinity
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Re: Road resurfacing

BBC Motorised Cranes were powered by either 240v AC, or 110v DC
One of my early jobs in Training, and soon after, was driving a variety of these cranes
Once, despite cable guards, I drove over a DC cable, the guard cut the cable.
There was an almighty bang....
I thought... Oh  s***
It turns out it was a regular occurrence !
H&S meant we all jumped off the Crane, and kept a safe distance until the DC power could be turned off.
Examples
http://tech-ops.co.uk/next/vinten-cranes-motorised-heron-and-peregrine/
http://tech-ops.co.uk/next/mole-cranes/

The Heron was fun to drive, it could crab sideways !!
pwatson
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Re: Road resurfacing

And then you got your wrists slapped by the studio sparks as you hadn't set the cable guard correctly in the first place Wink
Kremmen
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Re: Road resurfacing

If I can be boring and go back to road resurfacing ..
Hands up all those in favour of loose chippings  Undecided
Let's be careful out there !
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Re: Road resurfacing

Where is the "hands up" emoticon when you need it  ? ?    Cheesy
Infinity
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Re: Road resurfacing

Quote from: pwatson
And then you got your wrists slapped by the studio sparks as you hadn't set the cable guard correctly in the first place Wink

Latterly, the technique was to wrap a long thick rope around the power cable at the camera end, as on Camera cables on Pedestal mounted cameras.
When I progressed to being the Cameraman on the front of the Heron, I never did quite get the hang of which Pedal controlled the up/down movement of the motorised arm, and which controlled the  left/right rotation of the Camera  & Seat mount !
Heron pictured
"Exterminate"........

Back to Road Resurfacing...
Don't you just love the smell, sight & sounds of the Tar laying machine !!
pwatson
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Re: Road resurfacing

Both picture are of a Heron - The Peregrine was an all together different beast
http://www.tech-ops.co.uk/page147.html
Back on topic, none of the camera cranes would work well on a loose chipping surface Smiley
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Re: Road resurfacing

Quote from: Kremmen
Hands up all those in favour of loose chippings  Undecided

Both my hands are totally down!
Fortunately I believe the contractors doing Sheffield lay Micro-asphalt.

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Infinity
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Re: Road resurfacing

Quote from: pwatson
Both picture are of a Heron - The Peregrine was an all together different beast
http://www.tech-ops.co.uk/page147.html
Back on topic, none of the camera cranes would work well on a loose chipping surface Smiley

Thanks, I did a Google search for BBC Heron, and one option was this...
http://www.google.co.uk/imgres?imgurl=http://www.vitecgroup.com/Portals/3/Images/AboutUs/history-05-...
http://www.vitecgroup.com/Aboutus/Historytimeline.aspx
1967. They obviously got it wrong !
I thought it may have been another version of the Heron, one which I had not come across !

Peregrine reference & picture removed.
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Re: Road resurfacing

Quote from: PlusComUK
When someone touches or holds a live cable / terminal in their hand, the natural response is for muscles to contract, meaning you cannot let go of the Mains feed.

But only if you complete a circuit, you can touch a live wire all day long so long as you're insulated from Neutral or Earth, might feel a slight 50Hz (or 60Hz for the merkins) buzz, but nothing more... Cool
https://youtu.be/wMKe2PMenvk?t=3m35s
And if you do complete a circuit, your muscles contract and release with each pulse of the mains waveform so you can actually let go, it's constant DC current ( over a certain voltage of course) that's the killer as your muscles lock up completely and you basically cook from the inside... Shocked
nanotm
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Re: Road resurfacing

iirc its a tiny amount of current required regardless of voltage on dc that does the damage something like 0.06amps
https://www.physics.ohio-state.edu/~p616/safety/fatal_current.html found a link about it.
@op
the canopy on the paver they used on our road a couple of years back stood at 20feet, it was a weird all in one machine it ripped up the road on the first pass sucking all the old stuff through a recycling system then on the second pass laid the base layer of the road and on the third pass provided the top layer, it took them 2 days to perform this display though despite the road only being 2 miles long, strangely the old way would of taken them 5 days but lasted 5>10 years, the current method looked great for a few months before it started showing signed of use both methods would have employed the same 50>60 workers though so the only real difference is the new fangled machine contraption that clearly doesn't do the job as well as it should .....
just because your paranoid doesn't mean they aren't out to get you
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Re: Road resurfacing

Quote from: nanotm
iirc its a tiny amount of current required regardless of voltage on dc that does the damage something like 0.06amps

That is true and applies to AC aswell, but that's in stopping the heart (basically causing fibrillation), but there is a point where if the voltage is low enough, it can't break the resistance of the skin so the circuit can't complete (hence why a 12v car battery cannot shock you, and claims of them doing so are usually cause by the "shockee" shorting them out with metal tools!!), if you were to be shocked by say 120v DC, via grabbing of something (grounded electrical cabinet and an inappropriate tool for the job in hand), then the current running through you heats you up as it travels through your body and cooks you alive, which isn't a pleasant prospect... Shocked
Basically along the lines of this (except they're using 110vAC):
https://www.youtube.com/watch?v=Sol6uJo9pMM
pwatson
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Re: Road resurfacing

"It's the volts that jolt but the mils that kill"
I think you're over playing the heating effects, 100V at 100mA is only 10W - Not really enough to warm significantly
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Re: Road resurfacing

Quote from: pwatson
I think you're over playing the heating effects, 100V at 100mA is only 10W - Not really enough to warm significantly

And if you're hands are clamped to something (like a bus-bar) that's got, say, 30 Amps running through it (and through you)? Grin
pwatson
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Re: Road resurfacing

The you're dead well before the heating effect is causing problem Wink