Grounding Straps?

I notice some people hang a "grounding strap" from the frame of their car. These straps contact the road, and I'm guessing they're intended to
discharge static electricity, or something along that line. Has anyone ever installed one of these? Does it do anything beneficial?
Rob
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already grounded through the tyres. That may sound daft, after all, rubber is an insulator right? Well in the case of car tyres, the synthetic rubber contains carbon (not to mention lots of steel wires in the construction), which is a conductor, hence your vehicle IS always grounded. That is one of the reasons why a car is one of the safest places to be in a thunderstorm, as any lightning strikes to the car will be conducted away to "earth". Similarly, if a tall vehicle strikes an overhead power line, the advice is to remain on board, as you are quite safe until you try to get down. Unless you are able to jump WELL clear of the vehicle, you run the risk of the current arcing through you when your feet touch the ground (and you get electrocuted). Don't believe me? Well watch any Health and Safety video re electrical safety on construction sites or farms.
Having said all that, I do occasionally get a static shock when I am getting out of the car, but it depends on what I am wearing and stems (I believe) from a build up of static in my clothing when I shuffle off the seat to get out. A grounding strap isn't going to help here as it's me that has accumulated the charge, not the car, and so the charge discharges through my hand, into the door and down to ground. I've found that if I grip a metal part of the car when I get out until my feet have touched the floor, the charge doesn't suddenly arc, so I don't notice the shock. Presumably it dissipates more gradually. If you're not convinced, try getting out of the car without going anywhere near the metal work, then go and grab hold of a metal object (eg a railing) that is grounded and see if you get a shock. Note, this will only happen if your shoes have insulating soles. If they don't, then the static will discharge through them as soon as your feet hit the ground, and you won't notice it.
In short then, I'd doubt very much that fitting a grounding strap has any beneficial effect other than as a "placebo". But then again, you see so many cars fitted with them that presumably some people think they do something useful.
Not much help was I!?!
Best of luck,
Tim
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Tim, that's the word I was thinking of "placebo" :-) your post makes sense to me.
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Here's my theory: the car is "safe" (relative term, that is) because it IS NOT totally at ground potential. Kind of like aircraft that get hit by lightening all the time and fly on with no worries. They are not at ground potential, and the lightening just rolls over the skin, or punches in and out and goes on about it's merry business (which is to equalize it's extremely positive potential).
Picture yourself standing in the middle of a golf course, at ground potential when a bolt comes out of the sky. You are just a high piece of ground and are not going to enjoy the experience.
'Course, that doesn't explain why a bird lands on high tension lines and get BBQ'd... the antenna on the spotter car provided a path to ground--not a great one, but good enough for the mega juice on those lines.
I SCUBA dive all the time and I've NEVER, EVER heard of a SCUBA diver getting electrocuted by lightening. And salt water is the perfect ground. OK, maybe divers don't dive during thunderstorms, but you'd think....
Anyway, the best way I've found to avoid the zap getting out of a car in a dry climate, is to elbow/forearm the A or B pillar quickly while getting out.
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Raider Rick
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To bolster Tim's argument I have an example. About 15 years ago a friend of mine was driving a specialty vehicle designed to view incursions on the US-Mexico border. It was a heavy van type vehicle with a telescoping infra-red camera device. Anyhow he was out in the brush helping the local sheriff locate someone who had just robbed a store. It was quite dark that night and he wasn't paying enough attention to his surroundings when he activated the telescoping mechanism. The camera proceded up to its apex which I think was around 25 feet or so. Unfortunately, my friend had parked the van directly under some high voltage wires. They were those real thick ones; these transmitted electricity to a town of 30,000 or so. Well, when the camera contacted the wire there was a tremendous cracking sound and a bright light. My friend recognized what was happening and he leaped head first out the open door, careful to avoid any further contact with the vehicle. Laying on the ground, he saw the same thing occur (bang and light). Apparently, the system tried some kind of recycle or something. Well, after it was over he checkout his vehicle. The telescoping camera (about 1/2 million dollars) was welded together and all burned up. All four tires on the vehicle were melted and it sat there on its wheels. Then he looked around - no lights anywhere. My friend, Dale, had darkened one town completely and another partially. Quite an achievement! (are you somewhere reading this, Dale?) Anhow, the next day when he showed up at work, there on the duty board was a piece of an extension cord with a slice of burnt toast attached - his name prominently displayed above. jor

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These are not needed nowadays because the rubber in the tires are slightly conductive and bleed off any charge. Many years ago the tires were not conductive and the car could build up quite a charge as it moves down the road. In the "old" days, toll booths had discharge wires sticking up to touch the car's body so the toll booth operator and driver didn't get a whopping shock.
When you get a shock when getting out of your vehicle, it is because there is a charge on you relative to the vehicle. J

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So I guess it's safe to say grounding straps are a waste of money. Thanks for the many well stated responses.
BTW, I did install one, but as suggested found no benefits (I know... benefits to what?)
Thanks again.
Rob
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