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Thread: Fuse sizing

  1. #1
    shagmebaby
    So....... My boat is old and the wiring was add on on top of add on and no fuses in the whole deal. So I ripped it all out and started over from scratch. oversized all the wiring ,double jacket cable etc.
    My question is on the fuse size to use on stuff, like Ignition , stereo , gauges , power point etc. Anybody got teh scoop ??

  2. #2
    DMOORE
    IMHO, I would go with a breaker panel. Just about every size and shape is available from marine parts suppliers. My SportCat is set up with a 8 or 10 circut system and is very compact.
    Darrell.

  3. #3
    shagmebabe
    Thanks for the imput. I have purchased a marine fuse box, but I just dont know how big or small of fuse to use on the things previously listed.

  4. #4
    DMOORE
    Main power= 30 amp. Stereo and amplifier= 30 amp. Pretty much everything else 15 amp.
    Darrell.

  5. #5
    ck7684
    ...somewhere I have a great wiring book. It is geared toward hot rods but should be equally handy for boat wiring. I cant recall the title but I will look for it...

  6. #6
    SmokinLowriderSS
    Get a decent multimeter, and it does NOT have to be a $200 Fluke either. $10 to $25 can serve you forever, digital OR analog.
    Use DC AMPERAGE setting and test each circuit for actual draw, then fuze about 10-20% higher. Once all the small circuits are done, fuze the main about 10-20% above the max load (yes, this entails a little bit of reccord-keeping).
    A boat's lighting circuit may be as low as 5 or 6 amps usage, fuze at 10.
    If the steereo has a reccomendation, use it.
    Instrument cluster power may only be 3 or 4 amps, why fuze 15, go 7.5.
    The C/B idea is fine, but the same sizing needs apply.
    I run 2 fuze blocks, a switched one up front (gauge power, Nitrous, stereo, power outlet), a battery-hot under my hood (horn, lights, bilge fan & pump, elec diverter, AND the ign switch circuit main).

  7. #7
    widowmaker
    use as small of fuse as possible on every circuit. Most items will tell you what size fuse to run, i.e. fuel pumps, bildge pumps, blower motors.
    20 amp fuse for hydraulic place diverter
    5 amp fuse for gauges and gauge lights
    7 -10 amp fuse for most fuel pumps
    I also run a circuit breaker on the entire system that cuts power to everyting except the power to the starter,( not the solenoid ) the motor, that is hard wired. typically a circuit breaker about the same as the alternator around 65 -90 amps is a good starting point. Some of the old style ciruit breakers were only 30 amp and if you try to wire a big stereo to one of those it will pop.
    Most stereo head units use only about 5 amps.
    Amplifiers, well that is another story, I guess it depends how big they are.
    In most applications, 14 - 16 gauge wire is good for everything, except the starter solenoid which I would use 8 -10 gauge. If you have very large bilge pumps use 10 - 12 gauge. The Starter motor and ground to the block should be 2 - 4 gauge.
    Hope this helps.

  8. #8
    rrrr
    Wanna do it correctly? Circuits should be sized at 125% of load, absent manufacturer's specs. Correct wire ampacity is important, as is voltage drop consideration. Voltage drop is a function of current and circuit length (positive and negative footage combined). I size for 3% drop, but 10% is more common.
    Excessive voltage drop will overheat stuff and make it fail. Also, using marine grade wire is a good idea. It has smaller strands for more flexibility and is tinned to resist corrosion. I use crimp on terminals with heat shrink insulation barrels, and the barrel is coated with an adhesive that melts when heated. All expensive stuff, but once it's done it will never fail. West Marine sells the wire and terminals, Ancor brand.
    My v-drive wiring harness is going on its sixth season and I haven't had to touch it yet.
    If you follow http://www.boatus.com/boattech/CircuitProtect.htm this chart you will find the answers.

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