[K3] Why fuse the negative lead from a battery?

Posted by James Maynard-2 on Apr 02, 2011; 7:42am
URL: http://elecraft.85.s1.nabble.com/K3-Why-fuse-the-negative-lead-from-a-battery-tp6233377.html

I'm a new K3 owner, and I chose the K3 in part because of its small
size, because I intend to install it in my boat, which is already
cramped for space.

  I am re-wiring the boat to comply with ABYC (American Boat & Yacht
Council) standard E-11, /AC and DC Electrical Systems on Boats/.  I have
a conventional negative-ground DC system.  The ABYC E-11 standard
requires that in such a system, overcurrent protection (fuse or circuit
breaker) to protect the boat's wiring shall be in the ungrounded
(positive, red) conductor and that the grounded (negative, black or
yellow) conductors in branch circuits (such as the one that one powers
my ham station) shall /not/ have fuse or circuit breakers in them.

The /K3 Owner's Manual/, however, states (under "Specifications", on
page 8) that "[w]hen a battery is used, both sides of the battery cable
should be protected by fast-blow fuses."

I wonder why the manual recommends that the negative lead should be
fused? Can anyone explain this for me?

I intend to wire the K3 power lead with fast-blow fuse in the positive
(red) conductor only, in compliance with the ABYC E-11 standard.  But
,still, I wonder: why does the K3 manual recommend fuses in /both
/conductors: the black (grounded, -12V) as well as the red (ungrounded,
+12V)?

Jim Maynard, K7KK

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