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Old 04-19-2006, 07:25 PM
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fuse size for 8 gauge- main feed

I'm wiring my current project with the battery and a Ford starter solenoid mounted in the trunk. I'm using an 8 gauge wire (about 10' length) between the solenoid and my fuse panel under the dash, which will serve as the main power feed between the battery and the fuse panel (and also carry charging current between the alternator and the battery). My alternator capacity is relatively small, 63 amps.

As stated in previous threads on this forum, I know that I need either a fusible link or a fuse at the battery side of the solenoid to protect this 8 ga wire. Two questions-

1. What amperage rating of fuse or fusible link protection would be recommended for use on an 8 gauge wire?

2. I've read that fusible links should not be mounted in the passenger compartment due to the excessive heat (or small fire) that is generated if they open. I'm hesitant to mount one inside my trunk as well, particularly since my solenoid is located farly close to my battery, and my plastic fuel cell is even somewhat close. However, I've seen some plastic encased fusible links at the local auto parts store (made by Buss in various amp capacities between 50 and 80 amps) that visually look more like a fuse. Does anyone know if these type of fusible links have the same degree of fire hazard if they open as the more conventional type of fusible links?

Any comments or recommendations would be appreciated.
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Old 04-19-2006, 07:38 PM
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An 80 amp MAXI fuse will do it. Located within (1) foot of the battery.

The problem with fusible links is they are a factory engineered item for a specific application. (They are used only because they are cheaper than fuses).

I'm not familiar with fusible links from BUSS but if they are rated like fuses they are fuses.

vicrod
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Old 04-20-2006, 05:16 AM
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#8 AWG copper is rated at 50 amps. I know the wire will safely carry more, but that is just a general guideline. I would start with a 50 amp Maxi fuse as close as possible to the battery and see what happens.

I prefer fuses over fusable links, as they are easily replaced when need be.

Vince
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Old 04-20-2006, 07:25 AM
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disagree.
you want the smallest (30amp?) that won't blow when all on/all normal, you "want" the fuse to blow if "any" problem not a "major" problem...sounds like you are wired direct and only to the fuse box, many cars are not!

suggestion: use a 30amp blade fuse, very handy to pull and kill power into the car when testing,
"free" anti-theft protection, pull the fuse when parked, motor ain't gona' run

2nd suggestion....short #4 or so cable from the starter or the bell housing close to the starter to the chassis, you want the starter to use everything it can as a ground source to help the long cable loss

(more forgiving?) with the solonoid on the firewall, short cable to the starter, shorter solonoid feed wire into the car is my experience...try it if your having trouble....be sure the solonoid mt is a good ground connect

Last edited by red65mustang; 04-20-2006 at 07:42 AM.
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Old 04-20-2006, 09:41 AM
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Quote:
Originally Posted by red65mustang
suggestion: use a 30amp blade fuse, very handy to pull and kill power into the car when testing,
"free" anti-theft protection, pull the fuse when parked, motor ain't gona' run
Maxi Fuse is a blade fuse. To use as anti theft you need a small wire from battery + to maintain radio or ECU memory. Fuse that small wire with a 3 amp fuse and if it is blown when you get into your car you know someone tried to steal it.

Quote:
Originally Posted by red65mustang
2nd suggestion....short #4 or so cable from the starter or the bell housing close to the starter to the chassis, you want the starter to use everything it can as a ground source to help the long cable loss
Redundant, if you already have ground straps from engine to frame and frame to body. On a glass car run the - heavy battery cable from the trunk mounted battery to the bellhousing.

Quote:
Originally Posted by red65mustang
(more forgiving?) with the solonoid on the firewall, short cable to the starter, shorter solonoid feed wire into the car is my experience...try it if your having trouble....be sure the solonoid mt is a good ground connect
Bad design IMO, that means the long + cable from the trunk is hot at all times. With the solenoid in the trunk that heavy + cable is hot only while cranking.

Last edited by 302/Z28; 04-20-2006 at 09:49 AM.
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Old 04-20-2006, 10:41 AM
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good point 302/z28

"if" you have to use the solonoid on the firewall......even if the cable is routed inside the car.....insulate the XXXX out of it!

thanks...didn't recommend it...it was a "if" option.....

short ground cable = shortest best (copper) path to excellent ground source for the starter extreme amps draw, helps as the batt and starter get older (and the solonoid contacts arc decay) when starting a "soak" hot motor with lots of base timing....not redundant, more and better with a long cable to the starter

example from a recent thread, 32' with a pain to get to remote batt slow cranking..(is it the new batt or starter)...had him just hook his jumpers frame to starter motor for more ground...cranks great...
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Old 04-20-2006, 04:44 PM
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Doc here,

My wire Gauge Chart For stranded Copper wire, 7 to 10 feet Will carry 35 to 50 amps..So You want to fuse that at 50 amps to protect the wiring.

Use the Maxi Fuse in this application as Vicrod outlined and 302/z28..

Place it away from the battery and fuel cell as far as possible/Practical.

You Do not want to use the main buss power feed as an "Anti Theft device" at all..just too much to go wrong there..loss of memory presets, and in some Vehicles, you have to go through Computer "Learn" cycles again, and can leave you stranded in an intersection..when you least expect it.

I advocate the use of long ground Cable from the battery For one reason Only..All I ever deal with is Glass Cars..and ground there is at a premimun..If you have the extra..It won't hurt to use it. If not and have a solid body/frame..go that route..

Find out the total draw on your system, under Worst case conditions..Everything on..include brake lamps, backup lamps, heater blowers, A/C anything that uses power..use that figure to compare against your maxi fuse, and wire gauge..(If it actually can draw more than 50 amps..go higher on the wire/fuse)

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Old 04-20-2006, 05:07 PM
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Kinda ironic.....

I just replaced mine yesterday, it blew out... (mis routed starter wires touched the headers and burnt the insulation causing another short...blew my fuse..

I just used the same as what was in it before...a 50 amp large blade type 2.99 at kragen...I got it mounted on its block on the firewall behind the distributor..it'll save ya a fire
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Old 04-20-2006, 06:52 PM
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Thanks, everyone!
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Old 04-21-2006, 05:20 AM
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Quote:
Originally Posted by powderbill
Thanks, everyone!
Your quite welcome

Vince
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Old 04-21-2006, 06:52 AM
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your welcome

and thanks, Vince and Doc

no more "suggestions", only "food for thought".....

(LOL....Doc, your radio doesn't have "push buttons" for stations...."closest" thing to a computer in my car is a pertronix")

but that points out why no more suggestions, I was thinkin' old cars, old harnesses, doc is thinkin' newer "dang hi-tech stuff"

"an once of prevention is worth a pound of cure"
I'd still rather have a pretty "warm" 30amp fuse (breaker) than possibly 10' of constantly "hot" 8ga wire with a 50......in a old car with old harnesses and if for no other reason than posted above....cable shorted, (max load into the car harness was 30amps)
but newer cars do need about a 50 to be happy

Last edited by red65mustang; 04-21-2006 at 06:58 AM.
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Old 04-21-2006, 05:06 PM
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Doc here,

I doubt a 30 amp MAXI FUSE would support the system at all..

When you throw in combinations of Heater motors, and brake lamps, or Cooling fans and Tail/Turnsignal lamps .. You would far exceed the 30 amp MAXI FUSE..and If you were at a long Stop light..It could heat up enough to open..

50 amps is pushing the lower limit..IF the wire heats up, you need to re~evaluate the wire Size Vs Ampacity Vs link for the system..You may need 6 gauge wire..

The Alternator is Capable of 63 amps under adverse conditions..and If you have the lighting, Ignition coil, and other loads online at the same time, you may tax the system..Wire, and the Link ..

For instance, Heater on, (30 Amps for the blower/Defroster), and wipers (30 amps for wipers) And Brake lamps (15 to 25 amps) and any other systems, you can see the peak (Start up load) will exceed both the wire gauge and fuse size..the peak will drop after a short run time to a lower figure and Since a MAXI Fuse heats and opens over time, Peaks won't effect it that much, but over extended time it could open up if the load was constantly high enough , and long enough...(Like a road trip..) Or had a devastating load (opens right away)

This is why it is Important to evaluate the TOTAL draw of the system under worst case scenerio..(Full load on the system, everything Electrical ON) and match or slightly exceed the wire size and fusible link to that draw.

Red: Wish I had a Few "Pushbutton radios"..(even the floor selector type), I 'd restore them and re~Silk screen the dial Indicators, and Install some new Electrolytic caps for the old paper types, Align The RF/IF stages and install them (If for nothing more than that "Retro~Look") OR / And make a "Killing" on EBAY

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Old 04-21-2006, 07:08 PM
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"ouch" I totally missed it in powderbill's first post, he did say 63amp alt!!

powderbill, fuse needs to be approx/atleast 3/4 of max amp output =47amp=50amp fuse

doc, can that answer end the discussion? cause again your referencing new car loads (your vette? wow those are high) and I'm referencing old car with loads (and alt) to match.....see attached,
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Last edited by red65mustang; 04-21-2006 at 07:53 PM.
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