I don't know if this has been covered in detail, but a healey
lister was asking about fuse sizes. The answer I gave got way
longer than expected. But it could be important in preventing
fires!
----- Original Message -----
From Michael Lupynec <mlupynec at globalserve.net>
To: <Editorgary@aol.com>
Cc: healeys <healeys@autox.team.net>
Sent: March 6, 2000 1:42 PM
Subject: Re: Improving Safety and Reliability
> The simple purpose of a fuse is to prevent an amp overload in
the
> wiring.
>
> First - the fuse rating in amps should never be higher than the
> amp rating of the smallest gauge wire in the main loop parallel
> circuit being protected. Otherwise you are doing nothing
different
> than the house owner/tenant who sticks in a 20 amp fuse into a
14
> gauge (15 amp) circuit. When there's an overload or short the
> wires or may start to overheat before the fuse blows.
>
> Second - the amp load of the devices (eg auto lamp bulbs),
usually
> being much less than the wire rating, you can choose to put in a
> fuse rated just above the load amps and therefore well below the
> wire rating to make your circuit even 'better' protected. There
> are potential short or poor connection situations that don't
draw
> huge amps but can create a sparking or localized heat source
that
> may ignite a near by flammable material. Probably what happens
in
> most winter storage garage fires or trunk explosions, (usually
on the heavy wire
> starter circuit).
>
> To determine your amp load you don't just add up the amp draw of
> each device. There is a special formula for equivalent
resistance
> of devices in parallel, 1/Requiv=1/R1+1/R2+1/R3+....+1/Rn and
then
> amps=voltage/Requiv. Practically you might start with the wire
> rating fuse size and work your way down a little.
>
> There's a lot more detail technical stuff like excessive length
> of wire run, service rating and even wire ratings are
determined in a specific
> environment ie buried vs open air, ambient temperature etc. -
all
> that in normal automotive applications is normally not too
> relevant. Maybe british car circuits should have GFI's (ground
> fault interrupters) - built by LUCAS of course..
>
> Mike L.
> AN5 10426 etc
> NOT AN ELECTRICIAN - critiques welcomed
>
> ----- Original Message -----
> From: <Editorgary@aol.com>
> To: <rtrummel@san.osd.mil>
> Cc: <healeys@autox.team.net>
> Sent: March 6, 2000 11:59 AM
> Subject: Re: Improving Safety and Reliability
>
>
> >
> >
> > In a message dated 3/5/00 7:09:49 PM, fhunter@kcnet.com
writes:
> >
> > << >
> > >
> > > So what are your suggestions? Improving the safety and
> reliability of our
> > > cars is obviously important, >>
> >
> > Doug Scranton and I made one change to my Healey last night
that
> took fifteen
> > minutes and gives me much peace of mind.
> >
> > We took an inline fuse bought from the auto store and soldered
> bullet
> > connectors to both wire ends. Then we unplugged the red wire
> that comes up
> > from the chassis harness under the fuse block from its double
> connector and
> > plugged in one connector of the inline fuse. With an extra
> single female
> > connector, we hooked the other end of the inline fuse to the
red
> wire going
> > to the chassis harness. Presto, we have fused the rear light
> power circuit
> > (which, you may remember, also includes the nefarious license
> plate light
> > with its potential for shorting out the entire harness).
> >
> > Though some people recommend inserting an inline fuse between
> the light
> > switch and red wire at the dash, that seemed a bit more
> difficult and would
> > also have the effect of shutting down the headlights should
> there be a short
> > in the rear lights. If I had a second inline fuse, I think I
> could insert it
> > in the other red wire circuit, that goes back into the main
> harness, which
> > should provide separate fuse protection to the front circuits.
> >
> > Now the question for the electrical experts -- what strength
> fuse do you
> > recommend for a circuit that includes both tail lights, both
> brake/signal
> > lights, and a dual-bulb license plate light?
> >
> > Cheers
> > Gary Anderson
> >
>
>
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