Fusible Links

[maglinjosvinn]

by my count there's 3.

1 on the starter

2 on the alternator - one for the blue/white wire and one for the red wire.

i did some searching (yay me!) and i found that the fusible link theory is based solely on the 'size of yoru wire'. this ... well. cracks me up. i had my head stuffed in a dodge avenger's hood and saw ALL the fusible links in a nice neat row and labled in the under hood fuseblock. thought to myself. man. that'd be nice.

problem is. fusible link 'cartridges' don't come in 10ga Wire denotations.

they come in amp notation. so ah. yeah. lol. what SHOULD the amp protection be on each of these three wires? i'll be putting a fusblock outta a newer car into my OPEL (the car is a 91 GEO storm, has relays for door locks, fuses, diodes, regular 4 pin relays you name it) and it has plenty of room for my upgrades. even thinking about running the red wire for the headlights out to the engine compartment and back in again. cleanness matters right?

any the hoo. wondering about the 'amp protection' recommended on these 'links'. help very appreciated.

[brads]

I've always been told that a wires "amp" rating does not depend on what voltage you run through it (voltage= push) or anything else. Amperage is kinda like water running through a pipe. example: you can only get 1/2" of water through a 1/2" pipe. Doesn't matter what pressure you push it with. 1/2" is 1/2" and the like for 10ga wire. 10ga wire is rated for 30 amps and so, you can only get 30 amps through a 10ga wire.


10ga= 30amp
12ga= 20amp
14ga= 15amp

etc

Hope that helps,

Brad

[maglinjosvinn]

exactly what i needed to see. thanks.

[brads]

Hey Maglinjosvinn;

Hope you're still around. There's one thing you should probably ask somebody about before you do the work on your car. (sorry I forgot to mention this earlier ) Now, I don't know if this makes any difference (I'm not an electrician, I just asked the guys at work) but a wire is not meant to to run continuously at it's maximum rated amperage. In other words, if you run a 30 amp load continuously on a 30 amp wire... it will melt.

So, what's my point? My point is that I don't know if a fusable link knows this. Maybe you're supposed to put a 25 amp link on a 30 amp wire or something. I'd ask some reputable auto or maybe electronics shops first before you do the work.

Sorry for the inconvenience,

Brad

[maglinjosvinn]

haven't made the upgrade yet. thanks for the headsup. no worries, at least i got a spiffy/quik reply.

[Bill Hoffmann]

A fusible link is a wire about 6" long of a smaller diameter than the wire it is connected to, and it is covered with fireproof insulation. The purpose is to protect the wiring in case of a short circuit in a high current device such as the headlights (which are not fused) or a direct short to ground of a main wire such as the lead to the fuse block. Fusible links are usually sized four gauges smaller, so a 10 gauge wire would be protected by a 14 gauge fusible link. You can buy these at most auto supply stores with eyelets and crimp connectors already attached.

[maglinjosvinn]

the plan, actually, is it upgrade to a fuseblock. i saw fusible links under the hood of another car in little cartridge form and they read in amps. everything from 30 to 120 amps in his car, actually. *shrugs* looked very simple, just pull the cartridge if all else fails.

[rsefczek]

there's a little bit about links as well as links for sale at this website

http://www.madelectrical.com/catalog/fusible-link.shtml

hth bob

[soybean]

An excellent site with excellent advice and products. I've bought a lot of stuff from Mark. I just got a bunch of things from him last month for my current project. It takes a while to get him on the phone, but its worth it. Jarrell

[bq97]

Why buy them when you can make them? A fusible link is nothing more than a short piece of wire that is a thinner gage. The thinner wire can't dissipate the heat generated by the increased current load so it burns through in the event of a short protecting the rest of the circuit.

Also the water pipe analogy is incorrect. To say you can only get 30 amps thru a 10 gage wire is wrong. Wire is not rated for a specified current and will continue to carry a load until the heat generated destroys it. The shorter the duration of the increased load the less heat affect on the wire. A bare wire in open air will dissipate more heat than the same wire insulated in a bundle, therefore the bare wire will handle a higher current load. All wire has a given amount of resistance for the gage and distance. Reducing the thickness or increasing the length will result in a decrease in efficiency which generates more heat and will break down the wire sooner, that’s the whole concept with a fusible link.

By the way the recommended maximum amperage load for chassis wiring of 10 AWG wire is 55 amps, 12 AWG is 41 amps, and 14 AWG is 32 amps. BTW these are conservative numbers and of course operating environment and load duration are also concerns.

Brian

[Bill Hoffmann]

the plan, actually, is it upgrade to a fuseblock. i saw fusible links under the hood of another car in little cartridge form and they read in amps. everything from 30 to 120 amps in his car, actually. *shrugs* looked very simple, just pull the cartridge if all else fails.

Keep in mind that the fuse, fusible link, circuit breaker, etc. has to be located right at the source to be effective. A common misconception is that its function is to protect the device on the circuit. Instead, it is a safety feature designed to protect the wiring and prevent a fire. It would be tempting, for instance, to put a fuse block on the top of the GT's inner fender. The trouble is, if the feed to that block grounds out somehow, you have a meltdown and possibly an engine fire.

Because most of the car's individual circuits are protected by fast blowing fuses, fusible links rarely carry out their function. For instance, if your heater's blower motor siezes, a 15 amp fuse will blow, and the 14 gauge fusible link will not be damaged in the least. With that in mind, I don't see how installing an under hood fuse block will be an upgrade. If you are adding circuits for an audio amplifier, auxiliary lighting, etc., you could add a fuse block for those circuits, but I would recommend leaving the stock wiring as it is.

[jordan]

That is exactly how I want to have my auxillary lighting and electrical additions, I want to install a small gang fuse block under the hood but I can not get a definate answer if it is ok to draw power to that from the starter stud or the battery itself, from how I see it either would act exactly the same, though I can not have voltage spikes due to the ecu for the fuel injection system that I will be converting to. It seems that if I took power from one of the stock fuse block studs in the center it would be no different than taking it from the battery because there isn't that much added wire going to the fuse block that would act as a capacitor or voltage spike supressor. Any thoughts?

[bq97]

"Keep in mind that the fuse, fusible link, circuit breaker, etc. has to be located right at the source to be effective.”

That’s not correct. The protection device can be anywhere in the circuit. At the speed electricity travels a few hundred feet is insignificant. If this was the case the circuit breaker or fuse box in your house would be spread out over the entire home and the fuses in the car would not be centrally located. A fusible link or fuse element is normally at the beginning of the circuit in order to protect the entire circuit not just part of it.

“A common misconception is that its function is to protect the device on the circuit. Instead, it is a safety feature designed to protect the wiring and prevent a fire.”

It actually does both depending on the protection device selected and where the fault is generated. If the radio shorts internally the fuse blows to protect the rest of the circuit. If there is a high current situation somewhere else in the wiring the fuse might blow as the electricity follows the least resistive path thus saving the radio’s internals. That’s why household fuses might blow and circuit breakers trip in a close lightning strike.

”Because most of the car's individual circuits are protected by fast blowing fuses, fusible links rarely carry out their function. For instance, if your heater's blower motor siezes, a 15 amp fuse will blow, and the 14 gauge fusible link will not be damaged in the least.”

A fusible link is rarely used to protect a single circuit in the manor a fuse is. They are generally used to protect a number of fused and un-fused circuits from an over-current situation. Also, auto fuses are far from being fast blowing.

“saw fusible links under the hood of another car in little cartridge form and they read in amps.”

The little cartridge things are fuse elements. Fuse elements are generally for higher amperage circuits 30 -100 amps and are color coded depending on rating.

For Jordan:

Drawing power from the positive post on the battery, the stud on the starter solenoid, or the hot studs on the fuse block is immaterial; electrically it is the same place as each one connects to the other. Keep in mind these physical locations are all un-switched. The length of wiring alone will not prevent voltage spikes. The only way to prevent spikes from getting into the ECU is add a protection circuit but if the ECU was designed for a car it should have its own internal protection. I’m just an Electrical Engineer not a fuel injection guru so you may want to talk to a fuel injection guy about internal protection.

Brian

[asdasc]

I will second everything that Brian just said. I am an Electrical Engineer as well, working closely with all the Automotive suppliers and designers in Detroit. Nowadays, every module in the car, in fact ever pin of every connector of each module, is protected for short to battery, short to ground, and transients.

Transients are the real killers. Every time you turn on or off an inductive load (anything with a motor or solonoid) you get a voltage transient on the line that can shoot up to over 100v, but for a very short time duration. Due to the short time duration (milliseconds or microseconds) the wire or fuse never heats up or fuses open. But it can, if left unaccounted for, damage all the IC's. Our old cars don't have many (any?) IC's in them, so it is less of a concern, but if you add an Engine Control Unit for FI, you will.

As for tapping off the battery, the starter, or the center of the fuse box, just remember that if you add significant current draw to the system, that you will need to be able to support that on the exisitng wires to the starter or fuse box. Probably not an issue unless you are adding a significant load.

Good luck.

[maglinjosvinn]

*chuckles* i'm just saying i saw 'fusible link' section under a hood. is this a different thing? it clearly delinated 'Fusible Link' from 'Fuses' on the diagram. regardless i've been looking athis box i stole outta my GEO and it has a primary 'fusible link' *by the diagram* and it runs a bar down the one side of a slew of individual 'fusible links' next to this, on a different circle (after yet another fusible link) is a series of fuses. add in some relays for the door motors (windows and locks) and a series of 4 pin relays, a couple diodes, and you got my 'box'. ultimately i need a house for my relays, as i'll be upgrading to door motors soon, but currently i got this single relay just sitting on the brake arm as a testing circet for this damn alternator issue. *sigh* lol. i was going to run, say for instance, the starter cable that goes to the fusebox (with the fusible link in it) directly to the fusebox, through a fusible link, then directly into the car, following the original wiring specs, just with an extra 3 feet on either side of the fusible link. repeat this story for the two links on teh alternator.

at current, this project is postponed. i still need a way to mount this relay (prolly off the old studs for the old volt reg, but we'll see).

[kwilford]

Keep in mind that the fuse, fusible link, circuit breaker, etc. has to be located right at the source to be effective. A common misconception is that its function is to protect the device on the circuit. Instead, it is a safety feature designed to protect the wiring and prevent a fire. It would be tempting, for instance, to put a fuse block on the top of the GT's inner fender. The trouble is, if the feed to that block grounds out somehow, you have a meltdown and possibly an engine fire.

"Keep in mind that the fuse, fusible link, circuit breaker, etc. has to be located right at the source to be effective.”

That’s not correct. The protection device can be anywhere in the circuit. At the speed electricity travels a few hundred feet is insignificant. If this was the case the circuit breaker or fuse box in your house would be spread out over the entire home and the fuses in the car would not be centrally located. A fusible link or fuse element is normally at the beginning of the circuit in order to protect the entire circuit not just part of it.
Brian

Well, you are BOTH correct. And both wrong. Bill is correct in that if the wire shorts out BEFORE the fuse box, the wire between the source and the short will overheat. Brian's point is correct, but ONLY if the load (or short) is between the source voltage and the ground. The rest is semantics.

[bq97]

Brian's point is correct, but ONLY if the load (or short) is between the source voltage and the ground. The rest is semantics.

Hate to tell you but the load is always between the source and the ground, if the load is not between them its not in the ckt. Likewise a short is also always between the source and the ground. Where else could they be?

[Bill Hoffmann]

"Keep in mind that the fuse, fusible link, circuit breaker, etc. has to be located right at the source to be effective.”

That’s not correct. Yes, it is.The protection device can be anywhere in the circuit. No, it can't.At the speed electricity travels a few hundred feet is insignificant. That has nothing to do with it. If this was the case the circuit breaker or fuse box in your house would be spread out over the entire home and the fuses in the car would not be centrally located. You just made my point. A fusible link or fuse element is normally at the beginning of the circuit in order to protect the entire circuit not just part of it. Exactly what I said. Stated another way, if your fusible link was on the load end of the circuit, how would the wiring be protected if the wire grounded to the chassis?

“A common misconception is that its function is to protect the device on the circuit. Instead, it is a safety feature designed to protect the wiring and prevent a fire.”

It actually does both depending on the protection device selected and where the fault is generated. To use your home wiring analogy, the fuses in the fuse box protect the wiring, and the radio's fuse protects the radio. An electrician wiring your home has little knowledge of what will be connected to most circuits and it's not his concern.If the radio shorts internally the fuse blows to protect the rest of the circuit. Any overcurrent event blows the fuse to protect the wiring, if that's what you mean by the rest of the circuit, so I think we're just restating the same thing over and over. If there is a high current situation somewhere else in the wiring the fuse might blow as the electricity follows the least resistive path thus saving the radio’s internals. No. If some other device on the same circuit, such as a motor, drew excess current, it might cause a drop in voltage but would not cause more current to flow to the radio.That’s why household fuses might blow and circuit breakers trip in a close lightning strike. They blow when their designed current limit is exceeded, whatever the cause, but they're not designed for lightning protection, which is a high voltage event. I wouldn't count on them to protect that radio.

”Because most of the car's individual circuits are protected by fast blowing fuses, fusible links rarely carry out their function. For instance, if your heater's blower motor siezes, a 15 amp fuse will blow, and the 14 gauge fusible link will not be damaged in the least.”

A fusible link is rarely used to protect a single circuit in the manor a fuse is. Right. In my example the fusible link supplies the fuse block, which protects the individual circuits such as the blower motor. They are generally used to protect a number of fused and un-fused circuits from an over-current situation. True.Also, auto fuses are far from being fast blowing. Sure they are, especially when compared to fusible links.

“saw fusible links under the hood of another car in little cartridge form and they read in amps.”

The little cartridge things are fuse elements. Fuse elements are generally for higher amperage circuits 30 -100 amps and are color coded depending on rating.

For Jordan:

Drawing power from the positive post on the battery, the stud on the starter solenoid, or the hot studs on the fuse block is immaterial; electrically it is the same place as each one connects to the other. Keep in mind these physical locations are all un-switched. The length of wiring alone will not prevent voltage spikes. The only way to prevent spikes from getting into the ECU is add a protection circuit but if the ECU was designed for a car it should have its own internal protection. I’m just an Electrical Engineer not a fuel injection guru so you may want to talk to a fuel injection guy about internal protection.

Brian

Brian, I hope you don't take offense at the above, but when you quote my statements and say they're incorrect, I feel I have to defend myself. Anyway, I think in most ways you just restated what I wrote in the first place.

[wrangler]

OK... am thinking I have a pretty good grasp on this all,. but what I would like to know is, has anybody yet to come up with a decent replacement/alternative to the GT fuse block? I have always hated it, esp since I somehow seem to manage to dislodge a fuse from time to time. And when I say decent, I mean a block that can easily be installed using the current(no pun intended) wiring, screws, terminals, etc. If not, why don't we work on coming up with a decent alternative. Would be a great seller/money maker for the site, plus I am sure would sell well elsewhere(e-bay) as well. If this has already been broached, forgive my repetition. But I would think with all the engineering knowledge and farbrication skills present, this should have been resolved long ago. It may not be 'factory/original', but I think would be one modification that would be both welcome for its safety, if not convenience?
JAT...
Brett

[maglinjosvinn]

this might be getting off topic -

but. if you created a panel that 'emulated' the front of the fuseblock, so you can use the colored pigtails, then just mounted a regular handy dandy regular set of fuses behind it and ran the wires accordingly, i don't see why they're be an issue. i too hate those european fuses.

but. remember. its hard to find a space fuse thats in 8amps. hehe.



and did you guys know that the radio fuse was suppsoed to be 2.5 amp? or did my PO throw me a curve ball here?