The Amateur Amateur: Mobile Flambée
By Gary Hoffman, KB0H
This time, we
highlight the hazard potential of mobile installation power wiring. A
proper mobile installation should include adequate fusing.
Before installing mobile power wiring, you should first make sure the
wire will handle the required current. A check in the Component Data
October 15, 2001
The ARRL Handbook for Radio Amateurs should provide
a good guide. Adequate and well-placed fuses are necessary to prevent
fire hazards. For maximum safety, fuse both the
hot (positive) and ground (negative) wires near the
battery. Automobile fires can be both dangerous and
My wife Nancy and
I have been married for 30 years. I love her very much. I know she
must love me as well because she didn't yell at me when I set our car
We decided to
take a trip to England to celebrate our 30th anniversary. We were
leaving on the evening of Labor Day. Prior to leaving, we needed to
take our Labrador retriever, Thor, to the kennel. We all piled into
my car. Almost as soon as I had turned on the ignition Nancy said,
"What's that terrible smell?" Suddenly dense smoke poured
from under the hood.
Nancy, the dog,
and I bailed out of the car, our eyes streaming and our throats raw
from the acrid smoke. "I'll take Thor to the kennel," Nancy
managed to gasp. The implication was that I would stay home, figure
out what had happened, and prevent the house from catching fire.
Nancy and the dog made a fast transfer to her car and burned rubber
out of the garage before they asphyxiated.
I hustled down to
the basement to get some fans. I grabbed two and was struggling up
the stairs when a very loud siren began to wail. Cold fear gripped my
heart. Oh no, the garage is on fire! I thought. Fortunately that
wasn't the case. It was the first Monday of the month and St. Louis
County was just performing its monthly test of the tornado warning
I set up the fans
to blow the smoke out of the garage. I opened the hood of my car and
saw that there were no flames, so whatever had happened was probably
over. The smoke was still too dense for me to stay in the garage so I
retreated into the house and let the fans do their work.
When I was able
to re-enter the garage, I peered into the engine compartment of my
car. Everything seemed in order at first, but I finally spotted the
culprit. Some of the electrical wires I'd recently installed to power
my ham radio were fried to a crisp. One set of wires seemed intact
but the second set had been completely destroyed, the insulation
having literally burned off of them.
immediately what had happened. When I'd had a mechanic install the
wires, I'd asked him to run a set to the trunk to power my ham radio.
I'd also had him run a second set into the passenger compartment,
since I eventually planned to install a different radio in there. The
wires in the passenger compartment had been coiled up and put under
the floor mat of the driver's foot well. I had completely forgotten
One end of the
unused set of wires was connected to the battery. The other end,
lying under the driver's mat, had simply been snipped with a pair of
cutters. They weren't connected to anything. Foolishly, I hadn't
thought to cap or insulate them. Nothing had happened until that day,
when we were about to depart for England. Then fate decided that it
was finally time for the bare end of the positive wire to touch the
bare end of the negative wire. They formed a short circuit and
electricity flowed freely. The wires got hotter and hotter and
quickly melted their insulation, causing the acrid smoke.
My car with its doors and hood open--starting over again.
But luck was
with me. The car was undamaged, there was no fire and Nancy did not
strangle me with the dog's leash.
I used a pair of
cutters to disconnect the burned wires from the car's battery. With
great regret, I also cut the wires leading to the trunk and powering
my ham radio. They had been partially melted where they had come into
contact with the other set of wires, and by this time I was extremely
safety conscious. Thus satisfied that the car wasn't likely to burn
up, we went on our vacation.
Upon our return
from England, I bought some new wire. I was very gun shy at this
point, but I just couldn't
live without my mobile transceiver.
I also couldn't face the prospect of my hygienically challenged
mechanic looking under the hood, then turning his gaze to me and
slowly shaking his head, unable to believe that any creature on Earth
had done something so stupid. So, I decided to install the new wires
With my car's rocker panel exposed, I was able to follow the route of the
It wasn't so
terrible. I'd originally had the mechanic run the wires because I
didn't know where to put them, how to get through the firewall, and
things like that. This time I just followed the existing wires (or in
some cases, the trail of scorch marks). The wires leading to the
trunk were largely undamaged, but I replaced them anyway. The wires
to the passenger compartment were fried to a crisp in some places and
melted into a puddle of slag in other places. I scraped up the ashes
and peeled up the melted plastic and ran new wiring.
I did everything
the mechanic had done, with one notable exception. He had tied the
two sets of wires together and clamped them into the same lugs at the
battery. I installed completely separate lugs on the two sets of
wires and did not
connect the spare set to the battery. In
fact, I wrapped the spare wire lugs in so much electrical tape that
it will take a chain saw to free them. I also heavily insulated the
ends terminating inside the car, something I should have done the
first time. (Editor's note: Fuses also should have
been installed near the battery end of both sets of wires as well.)
Some melted remnants of the old wiring.
hypersensitive about safety this time, I double, triple, and
quadruple-checked everything. Every time that I touched a wire I put
a meter on it to make sure that it was the right one. I cleaned up
everything and spent a nervous ten minutes looking for a missing tool
(it had slipped into the crevice of the back seat). When I was
absolutely sure that I had done everything properly, I pressed the
power button on the mobile radio. Nothing happened.
I decided to
check the trunk first. Fortunately, the problem was simple and
obvious. I'd forgotten to plug in the radio. I quickly remedied the
situation, jumped back into the car, and tried the power button
again. The radio came to life! It hadn't been damaged. It hadn't lost
its programming. It worked just fine. I was ready for my next radio
adventure--as long as it didn't involve smoke.
note: ARRL member Gary Hoffman, KB0H, lives in Florissant,
Missouri. He's been a ham since 1995. Hoffman says his column's
name-- "The Amateur Amateur"--suggests the explorations of
a rank amateur, not those of an experienced or knowledgeable ham. His
wife, Nancy, is N0NJ. Hoffman has a ham-related Web page. Readers may contact
the author via e-mail,[email protected]
© 2001 American Radio Relay League