Ham Radio Fuses and Fire?

[chrismc]

Point is the negative fuse is not there as a mate to the positive side of the radio, but to protect the radio from being a return path for another circuit. IOW, the positive will open (maybe the negative, maybe not) if the radio circuit overloads, the negative fuse will open (positive probably not) if some other circuit shorts to frame or body ground. This is why you don't need it if you ground the radio to the frame, since there will be no ground loop created through the radio. But doing that might be counterproductive from a radio noise standpoint in some cases, particularly with our HF rigs that would be much more susceptible to it than an FM VHF rig.

Ok, in that situation the ground fuse does make sense. There is still an issue of the radio finding an alternate ground in the case that the ground fuse breaks (not always due to an overload condition). If the radio has juice on the positive side, but the ground wire has a broken fuse, then the radio will still be energized if it can find ANY ground. There's a good chance that it will find that ground via mounting hardware or the coax shield from the body-grounded antenna mount. If you have a 100W HF rig, then the last thing you want is all the power behind that rig surging through your coax braid when you key the mic. That coax will get smoked VERY fast.

I think I understand the recommendation for grounding to the body RIGHT NEXT TO the negative battery cable's body mount (with no negative fuse). The battery ground cable is typically near the battery, so your radio's positive and negative cables could easily be the same length. The amount of noise should be minimal if you are just a few inches from the battery ground cable. This would eliminate the possibility of backfeeding the radio's ground cable in the event of a battery ground cable that breaks loose, as well as the possibility of the radio finding a dangerous alternate ground in the event of an open ground fuse. After this discussion, this is how I will be re-wiring my rig.