Where to hook ground?

Hello everybody,     I am having some issues with trying to figure out where to connect a ground. Basically, I have a 12V light inside a metal structure, and
want to ground out the structure just in case the power wires of the light were to touch it. I just want a safety so there is no way I can get shocked since the system draws almost 7 amps. The rest of the system is very sensitive to EMI so it is crucial that this "safety ground" introduce no or as little as possible noise into the system. Also, is there some component I can put on this wire so that noise will not be able to enter the system through that wire, but will still allow it to ground out over 7 amps? Thanks a lot for everyone's time.
    -Jeffrey Smith
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I think you need to read up about basic electrical safety. Contact with 12 volts won't kill or even hurt anyone. Not even slightly. The light may draw 7 amps from a 12 volt supply, but a human body won't draw enough current to even be felt. Most automobiles are "metal structures" and nobody has -- ever -- been electrocuted or hurt by the 12 volt supply. Burns and fire risk, now that's another matter. I hope you won't be keeping gasoline in there. A short could generate a fair bit of heat. Adequate fusing of the 12v supply will see to that. Where does the 12 volts come from? A automobile battery?
It's not current, but voltage that causes "shocks". To get a shock, the voltage has to be high enough to drive a certain level of current through the body. The threshold of hazardous voltages has been put at 50 volts in some jurisdictions, but even then it would be very unusual to hear of harm from accidental contact. Start worrying around 100 volts.
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Sorry I mean "an" automobile battery. I am a bit puzzled. You appear to know enough about electricity to be aware of terms like EMI, and you have even heard of attaching things to wires to minimize this, -- but -- you think you can get a shock from 12 volts. This doesn't add up. How come?
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|> I think you need to read up about basic electrical safety. Contact |> with 12 volts won't kill or even hurt anyone. Not even slightly. The |> light may draw 7 amps from a 12 volt supply, but a human body won't |> draw enough current to even be felt. Most automobiles are "metal |> structures" and nobody has -- ever -- been electrocuted or hurt by the |> 12 volt supply. Burns and fire risk, now that's another matter. I hope |> you won't be keeping gasoline in there. A short could generate a fair |> bit of heat. Adequate fusing of the 12v supply will see to that. Where |> does the 12 volts come from? A automobile battery? |> |> It's not current, but voltage that causes "shocks". To get a shock, |> the voltage has to be high enough to drive a certain level of current |> through the body. The threshold of hazardous voltages has been put at |> 50 volts in some jurisdictions, but even then it would be very unusual |> to hear of harm from accidental contact. Start worrying around 100 |> volts. | | Sorry I mean "an" automobile battery. I am a bit puzzled. You appear | to know enough about electricity to be aware of terms like EMI, and | you have even heard of attaching things to wires to minimize this, -- | but -- you think you can get a shock from 12 volts. This doesn't add | up. How come?
I have felt the shock from 12 volts AC. I didn't die. But I didn't like the touch of it, either. That 277 volt shock at another time, though, was very painful. A couple 120 volts shocks felt in between.
When I was in junior high school, I had a friend who would touch electrical wires all the time and he said it didn't hurt at all. He'd willingly just hold wires at 120 volts and it had no effect on him. Then he'd prove they were live by touching them together with a big arc that tripped the breaker. When he touched the high voltage anode in an old CRT tube TV set, then he said those would hurt, but even then he had no qualms about working inside a running TV (his hobby was collecting old junkers from TV repair shops and mixing parts to get working TVs out of them). I asked him about color TVs and he said those did hurt a lot. Either this guy had very high impedance or very high pain threshhold. Many years later he died by suicide while on drugs. Sometimes I wonder if ... if he became an electrician ... would he do his electrical work hot?
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|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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snipped-for-privacy@cox.net wrote:

Risk of shock from 12V is essentially nil.

Is this "metal structure" located indoors or outdoors? If indoors, ground to the house electrical ground. Assuming the building's wiring is up to modern code that will ground to the Earth with a ground rod at the service entrance.
If outdoors either ground to a nearby building's service entrance ground rod, or get a ground rod of your own to drive into the ground.

If the "metal structure" is a complete enclosure, then grounding it is exactly what you want to do to keep EMI out. See: Faraday cage
Bill Ranck Blacksburg, Va.
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