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BigClive
06-16-2006, 12:31 AM
Stuning video of a lorry that's made contact with a line.

http://www.break.com/index/boompower.html

graybeard
06-16-2006, 05:32 PM
I hope no was hurt, but that was aqn awsome vid. I'm going to use it at a the next safety mtg.

riverhog14
06-16-2006, 07:48 PM
someone else posted that a few months back, still fun to watch!

BigClive
06-17-2006, 10:45 PM
Did the lorry driver get out. I shouldn;t think he'd be too comfortable sitting in the cab as the flames licked round it. Likewise any attempt to escape would have been dodgy given the amount of current passing to ground.

Trampbag
06-18-2006, 11:52 AM
Now, can anyone tell me what possible difference grounding this unit would have made, except to add one more point to burn and widening the step gradient. How much greater would the problem would have been if all equipment had been bonded?

Someone should show this to the safety engineer who thinks grounding and bonding all equipment together is a good idea. Better still, the safety engineer should be put in the middle of the mess.

BigClive
06-18-2006, 06:22 PM
Now, can anyone tell me what possible difference grounding this unit would have made, except to add one more point to burn and widening the step gradient. How much greater would the problem would have been if all equipment had been bonded?

I don't think it was associated with lineworks or even expecting that line to be there.

Bonding might have allowed enough current to flow to trip the circuit. Particularly if the vehicle was connected to a good earth point. I wonder what sort of potential difference was across the ground where the person filming was standing.

Amazing that it managed to blow the stabiliser in half and yet the crane rope itself remained intact.

Trampbag
06-18-2006, 08:20 PM
Equipment making contact with high voltage systems will act exactly like what is seen on this video clip. Just because it is not a line truck doesn’t make the properties any different. If the equipment around the vehicle making contact were bonded together with several driven groundrods it would just make it a bigger, larger area energised and burning, and more dangerous to anyone working in the area. Bonding and grounding equipment is not a safety factor and will not save lives or serious injury.

I would like someone to explain, in technical jargon not a rhetorical sentimental explanative, why I’m wrong. I maintain that this relatively new technique, I never heard of it 20 years ago, of grounding and bonding equipment is dangerous and misleading to linecrews, and is just one more “safety technique” initiated by non-trades people, without consultation with tradesmen.

Simply put, I believe a lot of accidents are caused by just this type of misinformation interfering with the sound judgement of experienced personnel in this trade.

riverhog14
06-18-2006, 09:43 PM
I think it was setting trusses on the house beside it, just a guess :). But if the vehicle was not grounded, and the driver goes to step off with one foot on the crane and another on the ground, hes just another path to ground. If the vehicle was grounded, the circuit might have tripped. Also, when that driver goes to step off, he wont get as much current going through him. Maybe enough to save his life. Correct me if Im wrong, but electricity takes all paths ground, but travels most on the path of least resistance (the vehicle ground instead of the driver).

Trampbag
06-18-2006, 11:35 PM
Let’s say for argument sake the live is138Kv. Within the first 8 seconds the pad was blown free of the rear right rigger thus making full metal contact with the ground. Several seconds later the front of the truck caught fire and started to arc, making a fine ground. All riggers were making great contact by this time, notice no tires were blowing nor even smoking meaning there are good paths to ground, better than the tires which usually blow quickly if unit is not well grounded.

Yes, electricity takes all paths to ground, and will travel most on one of least resistance more so, but at 138Kv humans don’t require a lot of amperage to severely mess them up.

I’ve seen a lot of these type videos and the aftermaths of accidents of this nature. Thank goodness I have never witnessed one first hand. In almost every instance if the operator had the balls to stay on the machine he survived, if not ultra serious injuries including death. Also the line did not trip until the power company operator or lineman tripped the line. I have seen sand turned to glass and ground rods or connections burn off while the equipment continued to burn.

Is there anyone out there who can explain, in technical terms, how a driven ground rod would have set up any more resistance thus changing the outcome of this situation?

BigClive
06-19-2006, 06:51 AM
Is there anyone out there who can explain, in technical terms, how a driven ground rod would have set up any more resistance thus changing the outcome of this situation?

A better ground could have increased the current flow significantly enough to trip the protection. Although the stabilisers seemed to be providing some form of path to ground, the arcing at every joint and around the base would suggest that there was still a significant resistance there. I'd guess that the pads were preventing a good enough connection for significant current flow. Dry ground wouldn't have helped either.

Looking up and then keeping away from the lines would have worked even better. If the driver was OK then I bet he has a good look next time.

thrasher
06-19-2006, 09:51 AM
Tramp:
I don't know where you have worked for your career that you have only seen grounding trucks recently. I started at a Co-op in 1978 and grounding trucks was old long established work practice then. I have seen the metal boom of grounded diggers get into the line twice and both times the upline device opened within a second. I have also seen a half a dozen ungrounded cranes get into 12.5, 69, and 115kv and only two (both on 69kv) opened the line the others sat and burned until we opened the line. I agree grounding does nothing to improve your odds on the initial contact, but it DOES shorten the exposure time and divert the majority of the current to and thru components built to handle fault current. One other point, for all three Co-ops I have worked at and, several others I know the rules at, there is a hierachy of grounding. 1st choice is the system neutral, 2nd choice is the pole ground, 3rd choice is an anchor rod, last choice is a driven temporary ground. Before you say so I do know of an accident at another Coop years ago with a temp ground that when the truck got into the line the ground rod was launched and the truck continued to burn. So grounding the truck just improves your odds and minimizes the damage.

Trampbag
06-19-2006, 07:00 PM
I guess recently was 20 years ago being the first time I experienced grounding units we were working with. I went to work in Southern Ontario and did not think much of it then. They did, however put stringing equipment on grounded steel mats which I thought was a good idea.

The UK did very little high voltage hot work when I was there and most Brits thought I was suicidal when I was gloving a 4Kv system in North Africa. Dead and grounded was their way.

I have experienced half hearted attempts to ground equipment since in Western USA and Canada. The East seems to demand it. But then the “North East” is ground to ground, lock to lock rubber gloves as well, which I don’t like or agree with. It all depends on what one grew up with and what one feels comfortable with. Also it depends upon what one experiences during a lifetime.

Many places do not have usable primary neutrals for example where delta exists, where the primary neutral is on the x-arm with the primary (California is one area that comes to mind), where the primary neutral is above the primary (Texas for one), and where the primary neutral is part of the secondary bus where triplex is used or is “spun” and there is little room for a connector. How about where Hendrix systems are use, does anyone really want a ground wrapped around that when energised at 14.4Kv? I don’t. Some utilities don’t want the system neutral used in case of contact and burn off.

The only way a driven ground rod can be reliable as a ground is when it is driven deep enough and megered to show enough resistance as to be a dependable ground or earth. As far as using the pole ground, come on. Many times it is # 6 solid, # 4 at best which would last about 3 cycles under heavy fault. Pole grounds are often enclosed in ground guards, sometimes in duct the full length of the pole leaving no access.

By all means, ground the trucks if that is what is required by your employer. I have no problem with that. I will never buy it as my protection, though, and anyone who does is living in a misinformed world. Grounding will never protect from electrocution should there be an accidental energising of the system or the equipment.

I want an equi-potential zone in my work space when that happens. I want a pole band below my feet when working on a wooden structure, I want the ground attached below my feet on a steel structure, and I want to be standing on a bonded mat if operating equipment while standing on the ground because there is no operating platform on the equipment.

I’m nervous as hell when all equipment is bonded together and I have to work in the middle of it. What a place to be when several units are on fire!

Yeee-Haaaaa!

thrasher
06-21-2006, 09:22 AM
Tramp:
I agree that you need your work zone protection and never tried to imply otherwise. It's just that I think truck grounding has it's place in the safety scheme as well. As to your comment about some places with small system neutrals. We have a lot of those on our system, however those small neutrals are in areas that only have 300-500 amps of fault current. Where we have high fault currents we have large neutrals.
One other point about truck grounding that you haven't mentioned. That is the groundmen. In an area with low fault current it is possible for an ungrounded truck to become energized and produce no visible sign because so little current is flowing thru the truck, however if a groundman touches the truck he will get zapped. So by grounding the truck we reduce the odds of creating a trap for groundmen. Before you say it, if the groundman is already touching the truck when it becomes energized then the ground will not help.
In summary truck grounding is not a primary protection, it is a second step to help the odds.

reppy007
03-07-2012, 05:59 PM
Stuning video of a lorry that's made contact with a line.

http://www.break.com/index/boompower.html

Thanks Big Clive............really a good video................as Poot stated the breaker at the sub might not trip..............great example...................just came across this thread

ratbastard101
03-07-2012, 09:34 PM
Let’s say for argument sake the live is138Kv. Within the first 8 seconds the pad was blown free of the rear right rigger thus making full metal contact with the ground. Several seconds later the front of the truck caught fire and started to arc, making a fine ground. All riggers were making great contact by this time, notice no tires were blowing nor even smoking meaning there are good paths to ground, better than the tires which usually blow quickly if unit is not well grounded.

Yes, electricity takes all paths to ground, and will travel most on one of least resistance more so, but at 138Kv humans don’t require a lot of amperage to severely mess them up.

I’ve seen a lot of these type videos and the aftermaths of accidents of this nature. Thank goodness I have never witnessed one first hand. In almost every instance if the operator had the balls to stay on the machine he survived, if not ultra serious injuries including death. Also the line did not trip until the power company operator or lineman tripped the line. I have seen sand turned to glass and ground rods or connections burn off while the equipment continued to burn.

Is there anyone out there who can explain, in technical terms, how a driven ground rod would have set up any more resistance thus changing the outcome of this situation?

I would say the fact that there were multiple places that were arcing is testament that there was not an effective ground. Yes electricity was going to ground it each point there was an arc but it was a high resistance path to ground. A low resistance path to ground does not arc to do there being no air gap between the to objects (in this case the energized truck chasis and solid ground) Wait a minute you may say that was dirt or parking lot or what ever.....is a hand full of dirt or sand solid? NO? So without a driven ground and solid tight connections there is no effective grounding of the chasis of the truck. The winch cable did not burn in two due to it made and maintained solid contact with the overhead powerline.....hence no air gap.....no arc.

If you have ever seen a set of protective grounds that have been properly installed and accidently closed in on you will see no spots where there was arcing at the connections since properly installed grounds are low resistance paths to ground using tight connections.

Would this have helped in this situation? With a properly driven ground near the truck chasis it could have provided enough current flow to trip the system protection devices (fuse, OCR, etc.). That is hard to say given the unknowns of the system in question. By having a driven ground in close proximity to the truck chasis, the step potential area would not have increased any more than it would be without a ground installed, and it would not have added another point for arcing since low resistance connections with no air gaps do not arc. Also with a good path to ground the other points that were arcing would have had less current available to sustain their arcs so they would have been smaller or non-existant. With all of the above said.....it is hard to say if a driven ground would have helped for certain, however it definately would not have added any hazard to the situation.

Thats what I believe to be true.....Im a lineman, not an engineer, so lets see what everyone else thinks.