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

Posted by Don Wilhelm-4 on Apr 02, 2011; 2:19pm
URL: http://elecraft.85.s1.nabble.com/K3-Why-fuse-the-negative-lead-from-a-battery-tp6233377p6233879.html

  Where will the current will flow if there is a fault?  That is the
question.

There are two things involved here - wiring the radio negative directly
to the battery or wiring it to the vehicle chassis.  It does make a
difference because of the way most vehicle batteries are tied on the
negative terminal.

If one wires both positive and negative directly to the battery, the
negative should be fused to protect the RADIO in case of a fault between
the battery and the engine block.  It is not a safety issue.

Note carefully that the battery negative is wired both to the engine
block and to the chassis by direct wires from the battery negative.  If
the battery were tied only to the engine block and then the chassis were
also tied to the engine block (as was pointed out in the case of the
boat), the failure mode would not exist.
And it is all because the radio is grounded to the chassis through the
antenna connection in addition to the negative lead.  If both these
grounds go to the chassis instead of the battery negative, the problem
solved by the fuse in the negative lead would not exist.

If the radio negative is connected to the vehicle chassis, the problem
does not exist and the negative lead should NOT be fused.

73,
Don W3FPR

On 4/2/2011 9:40 AM, David Ferrington, M0XDF wrote:
> I'm not positive (forgive the pun), but I think ideas have changed on that in the UK and you again don't fuse the -ve lead, but I'll need to check.
> 73 de M0XDF, K3 #174, P3 #108
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html