Burned ground wire

[gon2srf]

My Cobra WX 75XT CB has not been working well as of late so I took some time yesterday to check the antennae and wiring. What I found was quite disturbing. The ground wire from the power supply was burned to bare wire for about a foot towards a West Marine fuse box which provides a ground and fused power. The Cobra WX 75XT comes with a 5 amp inline fuse on the hot wire which is connected to the West Marine Fuse box where there is another 5 amp fuse.

The CB was still receiving power after the meltdown with a now bare ground wire completeing the circuit?! All my connections are soldered and crimped with the wires all protected with flexible conduit.

As I understand it ground wires melt due to heat caused from resistance. Could this resistance have come within the power supply or is my wiring/ground to blame.

All of my aux. lights, CB, HAM, aux power outlets all run through the same West Marine fused box. The fuse box is grounded direct to the battery with 4/0. Everything has functioned faithfully for 3 years until now.

The CB has been removed. I am going to open the power supply and check resistance. Does anyone care to have a shot at diagnosing the problem or have any advice?

[OLLIE]

I'm baffled on this one. One change I recommend is to run all your radios directly off the battery. It will give you better radio performance as well as allow the current to flow evenly from ground to positive. Are your wires the same size on the ground as on the positive wire?

[gon2srf]

I'm baffled on this one. One change I recommend is to run all your radios directly off the battery. It will give you better radio performance as well as allow the current to flow evenly from ground to positive. Are your wires the same size on the ground as on the positive wire?

Hi Ollie. Yes I beleive 16ga is the OEM wire size for power and ground and I matched it for the continuation. Correction on the fuses, I am pretty sure they are 15amp not 5amp. I would have gone directly to the battery but I was hoping to minimize the engine compartment connections. When I reinstall I'll go direct as you recommend and fuse the negative side as well.

[gon2srf]

I went out to the car at lunch and found the culprit. I replaced my Optima Yellowtop last month and the ground cable bolt had backed off was left barely attached.

My bad!

[cruiserlarry]

Yeeh, that'll do it alright... ground wires will heat up friom too much resistance - but when they touch metal they still ground. The bigger issue is when the same happens to the hot side - direct short.

Ollie's advice is correct - radio equipment works best when isolated from the rest of the vehicle's electronics, and vice versa - better to wire direct to the battery. CB radio, however, will do fine the way you have it because it is such a low power draw. With 4 watts output, it's drawing less than 1 amp in normal operation - not enough to interfere with anything else. I would suggest you put a much lower rated fuse (5 amp max)m on BOTH hot and ground side of the radio power wires - that would protect against surge damage, and possibly the resistance current that melted the wire cover....

[gon2srf]

Yeeh, that'll do it alright... ground wires will heat up friom too much resistance - but when they touch metal they still ground. The bigger issue is when the same happens to the hot side - direct short.

Ollie's advice is correct - radio equipment works best when isolated from the rest of the vehicle's electronics, and vice versa - better to wire direct to the battery. CB radio, however, will do fine the way you have it because it is such a low power draw. With 4 watts output, it's drawing less than 1 amp in normal operation - not enough to interfere with anything else. I would suggest you put a much lower rated fuse (5 amp max)m on BOTH hot and ground side of the radio power wires - that would protect against surge damage, and possibly the resistance current that melted the wire cover....

Thanks Larry. I have never fused the ground side of circuits but I will be doing so for my radio equipment from now on. I am not sure what size the OEM fuse was for the Cobra but I imagine it was 5 not 15 as I stated.

I'll be sure to reinstall 5 amp fuses on both sides this time around and run the ground directly to the battery.

BTW do you know what is considered a good OHM reading for my CB antennae cable?

[cruiserlarry]

Yeeh, that'll do it alright... ground wires will heat up friom too much resistance - but when they touch metal they still ground. The bigger issue is when the same happens to the hot side - direct short.

Ollie's advice is correct - radio equipment works best when isolated from the rest of the vehicle's electronics, and vice versa - better to wire direct to the battery. CB radio, however, will do fine the way you have it because it is such a low power draw. With 4 watts output, it's drawing less than 1 amp in normal operation - not enough to interfere with anything else. I would suggest you put a much lower rated fuse (5 amp max)m on BOTH hot and ground side of the radio power wires - that would protect against surge damage, and possibly the resistance current that melted the wire cover....

Thanks Larry. I have never fused the ground side of circuits but I will be doing so for my radio equipment from now on. I am not sure what size the OEM fuse was for the Cobra but I imagine it was 5 not 15 as I stated.

I'll be sure to reinstall as 5 amp fuses on both sides this time around and run ground directly to the battery.

BTW do you know what is considered a good OHM reading for my CB antennae cable?

The coax used for the CB is rated at 50 ohms...so, using a multimeter set to measure resistance, and the scale set to 100 ohms, place one probe to the center pin of the coax connector on each side. You should get a reading near 50 ohms; much higher, and you probably have a frayed conductor wire - much lower (likely near 0), and you might have a short to the ground shield. Either way, if it's not close to 50 ohms, replace the cable....

[gon2srf]

Yeeh, that'll do it alright... ground wires will heat up friom too much resistance - but when they touch metal they still ground. The bigger issue is when the same happens to the hot side - direct short.

Ollie's advice is correct - radio equipment works best when isolated from the rest of the vehicle's electronics, and vice versa - better to wire direct to the battery. CB radio, however, will do fine the way you have it because it is such a low power draw. With 4 watts output, it's drawing less than 1 amp in normal operation - not enough to interfere with anything else. I would suggest you put a much lower rated fuse (5 amp max)m on BOTH hot and ground side of the radio power wires - that would protect against surge damage, and possibly the resistance current that melted the wire cover....

Thanks Larry. I have never fused the ground side of circuits but I will be doing so for my radio equipment from now on. I am not sure what size the OEM fuse was for the Cobra but I imagine it was 5 not 15 as I stated.

I'll be sure to reinstall as 5 amp fuses on both sides this time around and run ground directly to the battery.

BTW do you know what is considered a good OHM reading for my CB antennae cable?

The coax used for the CB is rated at 50 ohms...so, using a multimeter set to measure resistance, and the scale set to 100 ohms, place one probe to the center pin of the coax connector on each side. You should get a reading near 50 ohms; much higher, and you probably have a frayed conductor wire - much lower (likely near 0), and you might have a short to the ground shield. Either way, if it's not close to 50 ohms, replace the cable....

Perfect, that is exactly what I needed to know. Thank you.