Message text written by "bschwart@postoffice.pacbell.net"
>I am setting up a fuse box with more than the three on a typical Spitfire
(but this would still apply) and was wondering what the overrating should
be for a given circuit. My thought was to run the selected circuit at full
capacity, measure the current draw, then add a certain amount over that for
margin. For example if the circuit in question was drawing 4 amps, I would
add ten percent and use the next highest fuse which would work out to a 5
amp fuse does this sound good, do I need to add more over for spikes etc.
or is there a better way?
Open for any suggestions
<
I believe that Dan pointed out that you don't fuse a circuit based on the
load, you fuse it for the size of the wire. The puepose of the fuse is to
prevent fires caused by overloaded wires.
That said, you size the wire based on the loads that it feeds. This may be
interpreted to mean you select your fuse based on load but there are other
factors that get interjected here. One is wire size standardization. If
you have a circuit with a 5 Amp load and another one with a 9 Amp load, it
still makes sense to us 16 AWG wire (or the British eq) in both cases and
use a 10 Amp fuse.
So my suggestion is to measure each branch circuit, and run either 16 AWG
(and use a 10 Amp fuse) or 14 AWG (and use a 15 Amp fuse) or 12 AWG (and
use a 20 Amp fuse) or 10 AWG (and use a 30 Amp fuse). (Note: the fuse
ratings are SAE ratings and if you use Lucas fuses, you need to convert the
ratings.)
This assumes you are running new lines. If you are using the existing
wires fuse according to wire size.
If you don't already have Dan's book, I recommend you get one. Although it
is TR6 oriented, most of it is quite generic and any car owner would
benifit from it.
Cheers
Dave Massey
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