Any tips to prevent hooking CB up backwards

QRN said:

Ken,the idea is that if the ground lead from the battery should fail.That is the point where the common ground on the engine block returns back to the battery.Without that lead there is no return current to the battery.If the radio is mounted such that the radio chassis is grounded to the vehicle body and hence connected to the engine block and the radio neg power lead is going to the battery direct as it should then the only path for the ground is through that neg lead to the common point on the block via the radio's chassis.The common point on the block means nothing unless it has a return path to the battery.Lift the neg lead off your car battery and replace it with a piece of 22 ga and hit the starter and see what happens.

Click to expand...

QRN, I understand what you are saying, but the probability of a scenario occurring as described is almost nill and if it does, very few if any electrical circuits will work correctly anyway - such as the starter solenoid. Then there is the fact that are numerous other paths back to the battery negative via the body, through other OEM ground wires, etc, so the current will find a path back to the battery if it exists anyway. If there are no paths, then there is no current flow, and the ground will need to be fixed anyway.

I do agree that if the battery negative cable is sized too small that it will create starting issues or fail, but again, this won't happen unless it is intentional.

So, while a fuse in the negative lead won't hurt, it really won't do anything to help either.

Chainsawgang said:

Hey DTB, Does the fuse in the ground side of your power cord work very well ?

Click to expand...

If your radio uses isolated grounding (circuit board capacitively isloated from power ground), it's ok. If your unit has the two ground systems connected, its basically useless because the current will flow right through the chassis to the coax ground and on to the main vehicle ground (doesn't do that in a magnetic antenna setup unless you grounded the coax).

I never bother with a fuse in the ground side myself, and I've hooked up my share of radios backwards. I've never seen more than the blown diode and rare blown audio chip or cap.

Chainsawgang said:

Hello TECHS,
I have an easy one for you guys, What is a good way to prevent hooking my CB/ 10 meter up backwards! (Besides just making sure red to red etc.) I slipseat & sometimes I come to work brain-dead on a Monday AM . Not to mention sometimes the leads could be mis- marked any ideas ??

Click to expand...

We have a bunch of non english apeaking dump truck drivers around here who are permanently brain dead.......if they can hook their radios up properly then you can. Don't sell yourself short.

i think he means adding a fuse to the ground lead-
and keeping the positive+ fuse in also.if this is what he means
i dont see were it would hurt your radio cause the rci2970 has this exact type of cord double fuse i call it.as for rating i go with whatever ya was running in the red wire.so if ya have a 5amp fuse then put 2/5amp fuses.as for blowing up radios hooking them up backwards im pretty sure the fuse is suppose to blow NOT the radio

DTB Radio said:

Chainsawgang said:

Hey DTB, Does the fuse in the ground side of your power cord work very well ?

Click to expand...

I never bother with a fuse in the ground side myself.

Click to expand...

Most of the fuses i have seen have a thin sowing needle like wire inside them. Would using one in line defeat the purpose of having a thick ground wire ?

I think by "ground side" he's talking about the negative power lead to the radio equipment. That thin wire in the fuse will carry the current that the fuse is rated for. It would be pointless to connect a 20 amp fuse (for example) in a vehicle's negative battery lead that's going to the chassis. THERE'S a recipe for fun!

Chainsawgang said:

Thanks Hotrod ! You win the prize ! That is exactly what I was talking about. Several of my buds swear by fusing both sides (+ pos and - neg) with the same size fuse will prevent damage to the radio. I just heard that you still need to make sure that the switch is turned off , then if you reverse the power wires : it will blow the fuses but , NOT DAMAGE the CB. :?:

Click to expand...

In almost 100% of the circumstances where the power leads are hooked up backwards, the protection diode will short too, so the fuse has not protected the radio. The fuse is designed/sized to protect the wiring going back to the battery so an electrical fire does not start, not to protect the radio.

If you already had the answer you were looking for, why ask for a technical analysis? Also, if you are so sure this will work, why don't you test it a few times and get back to us...

ground problem

I have worked at several dealerships as a line mechanic. I also have taught in the trade school to fill in for a semester. I have experience with this very problem. It happens more than you think.

The ground from the battery goes to the engine block on most cars. The problem comes when the block ground to firewall ground wire is left loose or left off when valve job or what ever is done and it is just left off. the starter and alt. are fine because the block is grounded. Every point of contact between the engine and chassis has a rubber mount. I have scene all kind of damage when a device or board needs a ground......it will find one and here lies the problem.

With the engine moving millions of times in the life of an auto....sometimes I have just found it to be loose or paint needs scraped off. Some cars at the battery ground the engine and the inner fender....this is better and this is what I always do(or run ground to firewall) especially when I am not barefoot.


hope this helps.....there are some guys here that are really smart.......I rarely have much to say around all these brains......


davis