The Jalopy Journal
Discussion in 'The Hokey Ass Message Board' started by JonF, Dec 12, 2014.
OK so what is the difference and why use one over the other?
One is easy to replace. The other takes longer.
A fusible link is just a piece of wire that acts like a typical fuse. Its a bitch if you don't know if your car has one or where to find it. ']
In some cars the power to the fuse block is a fusible link.
A fusable link goes where a "fuse" needs to be but can't.
Like Hilo mentioned, the power into the fuse box is usually on a fusable link as it should be. Generally they go close to the source of power so that in the event of an overload or short the majority of the wiring or cable is separated from the source of power and the potential for a fire is drastically reduced.
They should be on the alternator and at the starter, sorta easy to find and repair.
Get a copy of a Ron Francis Wiring catalog and read up on fusible links. I would never use one in my cars.
Certain cheap makes of cars (GM) used fusible links because they are cheap. Better quality cars like Chrysler products used circuit breakers because they are better even though they cost more money.
Fuses are in between, more costly than fusible links but cheaper than breakers, but easy to replace.
Especially Dodge pickups which had the fuse panel in the glove compartment.
Older cars (pre 80's, more or less) used fusible links. The technology for maxi fuses had not come 'round just yet. New cars all use Maxi-Fuses, easily replaceable. You may choose one or the other, but you MUST protect your circuits. A circuit breaker is not a desirable alternative, as the cycling could cause the fault to erupt in flame. This is considered bad. CBs are used in headlight circuits as a trade off between burning through electrical fire and crashing through not seeing.
P.S. Just so we're clear, a fusible link is a short length of wire 4 gauges smaller than the wire in the circuit it is protecting. It is designed to melt before the Fire Dept gets their boots on.
The reason the auto manufactures don't use fusable links anymore is because if the fire hazzard. It is just a piece of wire that burns when overloaded. Fuses just blow and cause no fire risk. Never use a fusable link on your cars. Like was said check in the Ron Francis catalog, they have a good piece on fusable links
These guys are saying use a maxi fuse instead of a fusable link. The protection provided is necessary.
At least that's what I hope they are saying
Everyone is close, but not quite....
A fusible link is designed to withstand an overcurrent for a longer period of time before clearing the overcurrent. A fuse will trip at it's maximum rating, within seconds if not milliseconds. A circuit breaker can take longer, but repeated cycling can damage them with occasional catastrophic failure, particularly in larger sizes. In some circuits, where the maximum current is seldom seen (like an alternator output, where max current is only seen after starting or if the battery is low), undersized wire is used (to save money). Use a fuse sized to the wire, and you have nuisance tripping. Size a fuse to the max load, and you let out the smoke. A link is a compromise, offering some protection.
Fusible links have a number of drawbacks, personally I wouldn't use any. Careful circuit design/installation will generally eliminate the need for them.
A maxifuse between alternator output and the battery and a maxifuse between battery and fuse block is normal.
I wire all my hotrods that way.
Woodiewagon - the Ron Francis manual is free and it is great. Thank you for suggesting it,.
All you other guys - thanks a bunch for all your very good replies.
I will not be using any fusible links.
Ron Frances makes a great product. I wired several cars and had no problems.
Maxi fuses perform a little differently than fusible links and are not recommended as replacements in older wiring harnesses from what I've read.. I have not read Ron Francis manual ,however...
I believe Maxi fuses ARE smart replacement, even in older wiring. As Crazy Steve was saying above and in his wiring series 101, you have to total the system demand and put in the appropriate amp fuse. The fuse needs to pop BEFORE the wire burns!!
I had a car with a fusible link that drove me crazy..I finally removed the entire wirinf from the car and rewired it and never had a problem again. HRP
I am glad for this forum, and that you take the advice of people and will not be using fusible lonks on your car. A very wise decision. This forum has a wealth of information, and everyone is more than willing to help
Next time you have a hood up on a Chrysler product look on the left fender well about 3/4 the way back. .In most cases depending on options you will see 5- 10 fuseable link wires, untaped poking out of the wiring harness. Fords you will find them at the starter solinoid
Remember the snap-in glass fuse size circuit breakers ? They came anywhere from 15 to 75 amps, made testing things cheap & easy, & were common in wrecking yards. May still be available from truck repair shops ...
And...Maxi is being used here somewhat- There are mini's,and the ol' atc's..... Regaurdless of the physical size of the protection device(fuse),it is still is rated for amperage......and will let go accordingly,or not, if an electrical system is well thought out. Food for thought.....Ahhh,those 80's Chryslers.....What a mess those were....
Know what your draws will be,and fuse/relay accordingly.
USE FUSIBLE LINKS!! Think of all the fun you'll have trying to figure out witch one burned!....hide some behind the brake booster like dodge did!.....(no wonder the Germans sold Chrysler back off)....man I'm glad I don't work on new shit anymore!
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Fusible links have their place, which is why they were used in the first place. Generally, they're used where the OEM or aftermarket manufacturer has tried to 'cut corners' and use wire that is too small for the possible maximum load but is adequate for the 'average' load. Think of them as a 'slow-blow' fuse; unlike standard fuses, they don't clear immediately in the face of an overcurrent situation, it will take more time for one of these to blow. This is a crucial difference; in the event of a 'overcurrent' beyond the 'normal' wire rating, depending on the amount of overcurrent and the time duration of that overcurrent, a fusible link may or may not open. As an example, a fusible link protecting a #10 wire may be able to withstand up to 100 amps if the duration is short enough, but may open at only 60 amps if the duration is long enough.
Fuses aren't that forgiving. A 60 amp fuse is going to blow at 60 amps if the time duration is longer than even one second. But it won't blow if amps are slightly below it's rating, regardless of time. As an example, let's say you're using a #10 wire from your alternator output to the battery and your alternator is capable of a max output of 90 amps. But 'normal' output needed to operate the car is only 30 amps, so you're well within the 'recommended' current capacity of the wire if everything is 'normal'. But if you have a maximum current increase (say if your battery is low and the charge rate increases to max until the battery is charged), current jumps to 90. A properly-sized link will pass this current until the output drops back off. To use a fuse, you need a fuse rated at 125% of max current or 125 amps (the closest available size large enough). This fuse will not protect the wire in the case of a partial short or overload as long as it's below the amp rating of the fuse.
Overcurrent protection is all about protecting the wire. If you're having trouble with fusible links, you have a problem with circuit design. And if you're using wire large enough for the maximum load, you won't need links....
Thanks Garyf for bring that up about Chrysler, they are one that use more fusable links than anyone else, Ford also was a big user of them
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