[OZAPRS] set up ford territory

[Michael Carey]

Hi Pete,

If you have a fuse on the negative wire then you will be "fairly" safe.  
You have to make sure that there is no possibility that your radio power 
cable, radio and antenna coax can ever take the full "earth" current of 
the vehicle.

If for any reason the negative battery strap became disconnected from 
the body/chassis/engine block then there is a possibility that your 
radio will provide the necessary path... and I'm sure it wouldn't 
survive the demands of a modern vehicle.  For instance on the new Ford 
utes there is only ONE wire going from the negative terminal to the body 
of the vehicle.

I had a situation with a SES rescue 4WD where the battery was isolated 
(when the 4WD wasn't being used) with a HUGE disconnecting switch and 
HUGE cable.  This was done on the negative side of the battery... it's 
perfectly fine to do this.

BUT, the Codan HF radio negative had been wired directly wired to the 
battery WITHOUT a fuse... thus bypassing the isolating switch!

The HF radio was not earthed at this stage as the HF antenna was 
incorrectly installed (the reason I was looking at the vehicle), the 
rubber mounted Codan antenna wasn't connected to the chassis, only the 
mounting bracket was... the factory fitted copper braid wasn't present.  
When I connected the earth properly to the Codan antenna, the WHOLE 
vehicle came to life, I had completed a circuit by connecting the earth 
to the chassis. A very big spark ensued and I quickly disconnected the 
earth to see what was going on... this was when I discovered the HF 
radio negative wire had been connected directly to the battery...

So if the earth on the HF antenna had been properly connected AND 
someone disconnected the battery using the isolating switch while the 
4WD was being used (on the chassis rail, easy to get to), the ENTIRE 
current load of the vehicle would have been going through the HF radio 
power cable negative conductor, then the RG58 coax and control cable to 
the HF antenna to the chassis...   The control cables and coax were 
buried under the flooring and I can imagine that a fire would have been 
quite possible.

I pointed it out to the SES guy who's eyes opened very wide... and I 
moved the negative wire of the HF radio power cable to the body of the car.

I always play safe with my radio installs and never NEVER connect the 
negative directly to the battery.

Michael.
VK5ZEA






On 27/05/2012 16:07, Peter Bye wrote:
> Re the below, why not??  I have done several mobile installs, most my 
> own, but also for others.  I always connect both +ve and -ve direct to 
> the battery, with a fuse on both.
> I also use rig runners for power distribution.
>
> Cheers
> de
> Pete VK2MPJ
>
> On 27/05/12 14:32, Michael Carey wrote:
>> ...
>>
>> Make sure you don't connect the negative wire to the battery... 
>> always connect to an earth point on the body, close to where the 
>> negative battery wire is connected...
>>
>> ...
>>
>> Michael.
>> VK5ZEA
>>
>>
>
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