[aprssig] Negative Fuses

Dale Blanchard wa7ixk at earthlink.net
Tue Jan 24 20:37:21 EST 2006

Ron wrote:
> While I would not want to burn up my D700 or car,  I can't help but 
> wonder why for many many years Motorola or GE  never put a fuse in the 
> ground of their commercial radios(tubes and transistors).  I don't 
> remember a single case of a destroyed radio or fire in a vehicle.  
> Kenwood about 15 years ago included a fuse in the negative lead, but 
> before that no one seemed to worry about the "Floating Ground".  Has the 
> automotive industry just gotten sloppy or what is the difference?  Today 
> many cars and trucks have a heavy ground to the engine block and a light 
> wire to the body.  Radio shops always got + directly from the battery 
> and negative from the metal case and a lead to the car frame (no fuse).  
> Today, most radio shops go to the fuse block and any convent metal dash 
> support.
> Ron
A fuse in the neg line is not  normally needed in a neg ground system.
There are still some Pos ground stuff out there were it helps.
Some radios are isolated and the radio itself is positive.
Yeasu is noted for that for that in the past.
If you measure between the neg lead and the chassis on some radios , 
there is no connection.
My GE commercial and Yeasu 857 comes with fuses in both leads and are to 
be hooked direct to the battery. Some commercial radios can be hooked up 
to a pos ground system that way.
All depends on the thinking of the engineer.
A fuse in the neg lead is only to prevent problems if the main ground to 
the battery and frame fails. Which is not very often.
Most vehicles have a ground to the frame and the engine.
Then the current can go thru the speedo cable and burn up the 
speedometer needle coil on the old type speedos.
Or it can take some other paths.
Some lap tops are pos gnd and can cause problems when hooking up to neg 
ground equipment.

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