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

[Samuel Strongin]

Who's on first     Sam kf4yox

Sent from my iPhone

On Apr 2, 2011, at 10:19 AM, Don Wilhelm <w3fpr at embarqmail.com> wrote:

>  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
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