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Author Topic: Mobile grounding safety questions  (Read 492 times)
KC0LGG
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Posts: 2




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« on: September 07, 2001, 07:08:54 PM »

I am about to begin a mobile HF installation in two vehicles, a 96 Toyota Camry and an 89 Jeep Comanche, pickup. I have been reading about grounding techniques and have some questions of about safe installation.

My main concern is the possibility of a fire or explosion from gasoline fumes.

1. Is it safe to use a drill under the vehicle frame and in the engine compartment where there may be faint traces of gasoline fumes? Can a spark from the drill motor ignite the fumes?

2. What about using a 100 watt soldering iron under the frame and in the engine compartment? Does the soldering iron present a safety hazard?

3. Since I will be working outside, it is likely that the only way that I can get high enough heat to effectively solder to the frame is to use a butane torch. This seems to be the most hazardous option of all. What is your advice/opinion about using a torch?

4. When doing work that involves any electrical wiring, I am aware that I must not offer an electrical path to ground through my own body. For instance I have been warned never to work on a car in bare feet, standing on a concrete floor (not a likely scenerio in any case, but I am glad I heard this advice). Likewise if working under the vehicle, I would place some wooden panels between my back and the ground under me or use a creeper. Any other safety tips that I should be aware of regarding working with the battery, wiring the power cords of the radio to the battery, etc?

5. Are there any other safety issues I should be aware of in addition to electrical and fire hazards?

Thanks in advance for you help.

Best regards,

Bob Stone, KC0LGG

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WB2WIK
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Posts: 20547




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« Reply #1 on: September 10, 2001, 04:39:46 PM »

Unless the engine is running while you're working on it, there is no high voltage present anywhere in your vehicle that can present an electric shock hazard.  The only voltage present is 12V from your battery, and 12V cannot create an electrical shock, if you grab it very tightly and are standing on the ground with bare feet -- you won't feel it.  This is one of the reasons that automotive electrical systems store power at such a low voltage, specifically to prevent electric shocks.  

Also, unless you have a gasoline leak, there should be no ignitable gasoline vapor in or near your vehicle when the engine isn't running.  With the engine off, the fuel pump is inoperative.  The only real probability for fuel vapor exists right at the filler tube to the gas tank...a place you really shouldn't be lighting any matches or making any sparks.

Drilling into and the chassis or frame is a common occurrance, provided care is taken to not drill through the gas tank or lines...and of course, be sure that you know what's on "the other side" of whatever you're drilling through.  I have no idea why you'd be using a soldering iron in the engine compartment or under the frame.  Most automotive power connections are crimp-type that require no soldering, right up to and including connections carrying a great deal of current.  

I would not use a torch to solder to the frame.  What's the purpose of this?  Normally, low-resistance contact to the vehicle chassis, frame, or wiring is done with nut-and-bolt connections and use of anti-oxide compounds.  

If you're unsure and shaky when working around 12V wiring in your vehicle, I'd recommend you take the vehicle and equipment to be installed to a reputable installer of 2-way radio equipment and/or automotive sound systems and have them do it.  Being shaky while working is a nearly sure way to make a mistake.

FYI, the most common "accident" that occurs when working with or around 12V automotive electrical systems is burns created by jewelry worn shorting out the + and - 12V connections!  And that's serious.  If you have a ring, bracelet, necklace or whatever and that metallic jewelry shorts out the 12V bus, the jewelry can become very hot, very fast and cause nasty burns.  It's a good idea to remove all jewelry (at least, anything metallic) prior to working around automobiles.

73 de Steve WB2WIK/6
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INITZERO
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Posts: 102


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« Reply #2 on: September 28, 2001, 04:31:44 PM »

> My main concern is the possibility of a fire or explosion from
> gasoline fumes.

    A few years ago when my brother first got his driver's license, he
decided that his car needed a awesome stereo system. Since the
car only cost a couple grand, I'm pretty sure the stereo eventually
cost more than the rest of the car. (Unlike my ham gear. {sheepish grin})

    Anyway, in our driveway, he was drilling holes in the floor of the
trunk so he could screw the amp down. He didn't have the right size
screws so he didn't get around to finishing the project that Sunday.
Monday morning, he drove to school and noticed that his car smelled
like gas. He didn't think too much of it at the time. The smell was still
there when he got home.

    It turns out, he drilled four 1/4-inch holes in his gas tank. We think
he didn't explode because he was using a sharp drill bit (not as much
heat generated as a dull bit) and the tank was full (more liquid -- not
as explosive -- than fumes).

    The moral of the story is use a sharp drill bit, keep your tank full
and know exactly where you're drilling before you drill.


> 1. Is it safe to use a drill under the vehicle frame and in the engine
> compartment where there may be faint traces of gasoline fumes?
> Can a spark from the drill motor ignite the fumes?

    Yes, it's possible. However, unless you have a gas leak and are
doing the drilling in a closed garage with no ventilation, you need
not worry. As my brother's story demonstrates, gasoline isn't quite
as explosive as most folks thing it is. If you ensure good ventilation,
you will not have any problems.


> What about using a 100 watt soldering iron under the frame and...
> ...high enough heat to effectively solder to the frame...

    I've installed a lot of stuff in my car and have never had to solder
anything to the frame. If you're trying to find a good ground, just find
a bolt near the radio that's already screwed into the car. Take that
bolt out and put your wire under it using a eye connecter on the
end of the wire. That should be all you need.


> I am aware that I must not offer an electrical path to ground through
> my own body.

    While that is certainly true, it is not as great a concern when
dealing with your car's electrical system as with your home's.


> I would place some wooden panels between my back and the
> ground under me or use a creeper.

    That really isn't necessary. Though I wouldn't be the first to try it,
you can touch both sides of your car's battery and not feel a thing.
Not even a tingle. While there are plenty enough AMPs there to do
some damage (car batteries often have 600-1000 amps while your
lucky if your house has 200), you're not a very good conductor at
the car's voltage (12v).

    As another noted, just make sure the car is off and you're fine.


> Are there any other safety issues I should be aware of in addition
> to electrical and fire hazards?

    While I certainly admire your caution, you panties are in a wad
for no good reason. Automotive electrical work is fairly straight
forward and safe. Use common sense (don't lick any wires) and
you should do just fine.

    If you aren't sure of yourself or just want a job that really looks
professional, visit your local stereo shop. Those guys tear open
cars eight hours a day and know how to put them back, too. It
shouldn't take them more than a couple hours (if that long) to run
your coax and electrical connections. At $45 an hour or less for
labor, it's often best to let the professionals do the work.

   Matt (k4mls)
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