Re[2]: Which battery lead to disconnect first

[Richard Welty <rwelty@domain.elided>]

On Mon, 13 Jan 2003 20:11:44 +0200 John Fielding <johnf@domain.elided> wrote:
>  Both stated that the negative lead should be
> disconnected
> first.  One even went so far as to say "disconnect the negative lead
> first as this will
> not produce a spark if current is flowing, whereas the positive lead can
> produce a spark
> which can ignite the battery gassing products".

the principal concern is that if you are using a metal wrench, and you
disconnect the hot lead (positive in a negative ground vehicle, of course)
first, you may make contact with something grounded which is where the
spark would come from (and if it's something for which a lot of current can
move, you could have a fairly spectacular spark at that.)

as far as battery isolation in race cars goes, i don't know FIA rules, but
i know SCCA rules, and our principal goal is that when the cutoff switch
gets hit, the engine halts immediately, all fuel pumps shut off, and there
is no chance of a spark which might ignite any fuel that is present. given
this, i really don't care which lead gets cut, so long as these conditions
are met. it's generally easier to do this in the hot lead, so that's what
gets done, although just cutting the hot battery lead won't shut down an
alternator equipped car -- at least not immediately.

cheers,
  richard
--
Richard Welty                                         rwelty@domain.elided
Averill Park Networking                                         518-573-7592
              Unix, Linux, IP Network Engineering, Security
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