The original advice in the MPT1362 UK Code of Practice was that the negative fuse to the battery terminal should be 3 times the rating of the positive to minimise the odds of a negative blow and full rig load to chassis via the coax outer.
As stated, CoP advice now (FCS1362) is direct to chassis, no fuse.
That does insert a small common impedance which will increase vehicle electrical noise into the Rx and increase risk of Tx RF into vehicle electrics. However that risk is regarded as lower than the fire risk of the MPT version.
Both versions are available on the web with a google or similar search.
Regards 73 Alan G0HiQ
--- On Wed, 17/3/10,
[hidden email] <
[hidden email]> wrote:
Date: Wed, 17 Mar 2010 11:49:14 -0400
From: "Paul Christensen" <
[hidden email]>
Subject: Re: [Elecraft] Connecting Transceivers in Vehicles - Change
ofRecommended Practice -
> This becomes a problem ONLY when the radio is connected to the negative
> terminal of the
> battery. In that case, you should use the negative fuse...
But consider that case where a rig is powered through a pair of fuses
home-run to the battery posts. If the negative fuse blows and the positive
fuse remains closed -- and *if* the radio chassis is common to negative
power with grounded connectors (e.g., SO-239) via a ground return through
the vehicle chassis, then the coax braid and other supplemental grounded
leads on the radio chassis will carry the full rig current.
Seems like in all cases where the rig chassis is common to the negative
power lead, the negative lead wiring should go un-fused at or very close to the negative battery post.
Paul, W9AC
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