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On a number of fairly modern rigs I've seen that both power leads are fused:

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Why is this still so?

Does this have something to do with some vehicles having a ground-positive system or is this simply a forgotten relic that needs to disappear as quick as possible?

If the fuse (in the negative lead) needs to go, what would be a safe and proper solution?

Related: How do I power my radio in a vehicle mobile install?

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captcha
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1 Answers1

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According to Alan K0BG's page about wiring, the negative lead is fused because of the possibility of a faulty ground elsewhere in the vehicle, which could cause excessive current to flow in the negative lead to the radio.

Here's a diagram from Alan, showing how to properly wire power to the radio: how to properly wire power to a ham radio in a vehicle

Alan's page about wiring, and the rest of his site, are chock-full of excellent advice about mobile ham radio.

rclocher3
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  • This is especially important given that the radio has another path to ground that's capable of high current -- the antenna cable shield. – Dave Tweed N3AOA Aug 23 '16 at 01:15
  • So is there any merit then in K0DEN's comment of my linked article which suggests that if the fuse in the negative lead is open circuit a potentially large number of amps will run through the antenna's ground connection and is considered bad practice? – captcha Aug 23 '16 at 02:05
  • Interesting! Tom W8JI is a very capable and well-known engineer himself; he designed Ameritron's amplifiers, which are very well-regarded, even if they are made by MFJ. Also he has an first-rate website and is regarded as an expert on grounding. Both sides of this debate make excellent arguments, although after reading what Tom W8JI wrote it seems to me that maybe a fuse in both the negative lead and the coax shield connection would be best. The jury is clearly still out; in the meantime I'd probably side with Alan K0BG, if only because he has such a beautiful website ;) – rclocher3 Aug 23 '16 at 19:52
  • I agree with sticking to K0BG's website. It is considered (one of) the most complete guides to mobile installations. By following his collection of installation guides I have successfully installed in various vehicles, never encountered any serious problems. – Edwin van Mierlo Aug 25 '16 at 06:57