If you re-read the post, what i was saying was that if he used a thin enough wire, the wire would act as the fuse, and not the fuse itself. Even if the fuse was only 1 amp, if the wire wasn't able to handle 1 amp (it's entirely possible), it would blow/melt/whatever before the fuse. This could be caused by wire stress, or any other number of factors. Just in case anyone doubts any electrical or computer info I give on this board, I have a bachelor's in electrical/computer engineering. I believe in yotatech's stance on misinformation as well, and wouldn't post unless I didn't know something about what I was talking about.
Russell

edit: i'd like to add that this has actually happened to me before with the stock inline fuse of the radio shack CBs. their craptacular plastic fuse holder melted from the heat of the wire before the 1amp fuse ever blew. needless to say, i caught it in time and replaced the wiring/fuse assembly.

 

The wire being too thin is feasable but not I do not think it is likely.

A stock CB is a 4 watt radio device, all of them I have seen have 1 amp inline fuses. You would need a pretty thin wire to not handle 1 amp.

Anyways, I'm glad no one was hurt and property loss was almost nill. Thats all I have to say about this.

Lamm

 

ditto

 

All the above sound like good ideas but it really sounds like the wire was probably chafed from install and ground out at the fire wall. To confirm this we would need to ask if there was any melted wire on the inside of the cab.
If there was no problem inside the cab then it was power wire grounding out.

 

A fuse at the source protects the wire & the vehicle in the case of a short, a fuse at the other end protects the device installed.
As to my credibilty I have been a caraudio installer for 15yrs.

There was a short under the dash & the wire burned to it because there was no protection at the batt.

 

[QUOTE=GSGALLANT]You should be able to squeeze about 12 amps through 16 guage wire at the length that you've run it. What size fuse did you have on the line? The max fuse size I would put on that particular setup is 10 amps (otherwise, your wire becomes your fuse). [QUOTE]

Have you got a good reference for determining fuse size? I've been wiring a lot of accessories and just winging it on fuse size at the battery. I'd like to know if I'm in the danger zone or not.

 

fuse size is determined by how much power you'll be drawing... lets say you have a 55W offroad light.

P=V*I
55W = 12V * I
I = ~4.58 Amps

In this case, a 5 Amp fuse should do the trick. Just be sure to add up the Power usage for everything that will be on a single fuse.

Edit: my carputer draws 75W max, so I use a 10A fuse for that.

 

So you're saying there's a difference between wiring it like this:
[Battery]__[Fuse]__________________________________[Device]_____<ground>

and this?:
[Battery]_________________________________[Fuse]___[Device]_____<ground>

I don't belive that. Sure, there's less chance of error if you screw up wiring the power wire, but electrically, nothing has changed.

Maybe if you fuse it on the ground side, but even then the device *could* still be fried if the power wire was shorted, although it is unlikely. That's why you're supposed to wire switches and stuff on the ground side of the circuit.. it supposed to prevent current loops in case of a short.

 

That's a fine equation boogy, but I need to know how the wire size variable fits into that equation.

 

Uhhhh Yeah, much more chance of a short between the battery and fuse Not much chance of a short developing in 5 or 6 inches as opposed to 5 or 6 feet.

 

I know, this is what I have been trying to tell people all along.

Just think of wires as pipes and electric current as water, you CAN'T shut off the flow if the valve is downstream of the break!!!

Lamm

 

Step one is figure out how much current will be going through your circuit. Step two, is choose your fuse size accordingly (slightly higher than the highest current you expect to see in the circuit). Step three is choose your wire so that it can handle the fuse current for the particular length of wire you are running. You want your fuse to blow before your wire melts.

See reference table attached here to choose your wire size.

Hope this helps. Let me know if this wasn't what you were looking for.

 

Yes thanks, that was what I needed.

 

My point was that it shouldn't matter if you place the fuse close to the power supply or not if you do your wiring correctly (i.e. choosing the correct wire gauge and using the correct fuse size).

If someone has to worry that much about a short occuring because they didn't place the fuse close to the power supply, then there is something horribly wrong with their electrical wiring and it won't matter where you place the fuse in that case.

Edit: Look at various car manufacturers. Some of them place the fuse blocks in the engine compartment close to the battery, some place them in the vehicle cabin further away from the battery. Do the cars with the fuse block in the vehicle cabin have more chance of an electrical fire? NO! Because the wiring was done correctly in the first place.

 

Interesting analogy.. except for the fact that with electricity, when the "pipe" breaks, the "water" stops flowing...

edit: i believe the water analogy you're referring to only applies to multiple current paths, not to breaking the flow of electricity. in that case of multiple paths, the electricty flows through the wire with the least amount of resistance, much like water will flow through the pipe with the greatest diameter.

 

My last truck had a fuse block under the dash. It, in turn, was fed by a fuse in a fuse block all of 6" from the battery.

Also, you seem to be missing an EXTREMELY important function of fuses: to protect against direct shorts to ground before the load, which are the electrical equivelent to, say, a broken water main. And unless you're really anal about routing and securing your wiring (and using solid/heavy stranded wire, which can be a pain in automotive applications), there's enough of a chance of that happening due to wires rubbing against other things to make leaving more wire than necessary unfused a really bad idea.

 

Yep, and in my truck the power suppy to that fuse block right near the battery starts with a fuseable link.

I guess in a perfect world we wouldn't need any fuses, but ˟˟˟˟˟ happens. Even if the wiring is perfect to start with, trucks and cars crash, people install headers that melt wire insulation, rubber gromets split, rodents chew wires,...etc

 

boogyman there is a main fuse near the batt before the internal box.
& dude your way off base with your understanding of wireing.
Think about this you have all your wireing all perfect & you have a wreck or you roll your truck over off road & you end up with a wire getting cut & you have a fire & your truck gets burned to the ground because you had the fuse in the rear.

 

HAHA! i'm sure you've had lots of experience with electronics and wiring so tell ya what; you wire your truck however you want to, and i'll stick to wiring my own.

p.s. there's no "e" in wiring.

edit: I seriously doubt that an electrical short will happen 6in from the battery vs. 3ft from the battery (where I happen to have my alternate fuse block wired on my rig). If you feel safer wiring your fuse right next to the battery, that's fine. When I wired up my alternate fuse block, I actually took the time to figure out all the equations, get the proper size fuses, and the proper gauge wire. Fact is, the original subject of this board (the electrical fire) could have been caused by almost anything; a blown fuse, improper wiring, whatever. My first post in this thread was just to throw out an idea that the wire gauge was too small, hence acting like the fuse if the fuse was too large for the circuit --something that *could* have been the cause, since no one on here seemed to come to any logical conclusion as to what *actually* caused the fire. Now I don't know about you guys, but I've seen lots of vehicles with fuses all over the place. A lot of them not necessarily right next to the battery. If you place the fuse further away from the battery, could the wire get frayed? sure. Cut? sure. Shorted? sure. Nibbled through by the furry animals that live in your basement? sure, why not. I know just about everyone on here cares as much for their rig as I do, and if you're as meticulous as I am about wiring and setting things up, I'm sure it wouldn't really make a difference if you placed your fuse 2 feet further away. But like I said earlier, if that's what makes you feel safer, by all means, go for it.

"Focker Out"

 

Did you also make absolutely sure that your wiring is not able to rub up against anything that may wear away insulation?
how's a blown fuse going to cause a fire?
Actually, I think many of us came fairly quickly to the conclusion that the wire insulation was worn away, and a short to ground occured somewhere between the battery and the fuse.
Actually, pretty much any fuse you'll find in a stock vehicle, if not close to the battery, has its wiring protected by something as close to the battery as practically possible. If it wasn't, and a few electrical fires happened because of that... can you say recall?
I just don't see a point in putting a protective device farther away than reasonably possible... it's just unnecessary risk. Even though I was extremely careful about how I ran the DC wiring for the inverter I installed in my work van (600A inverter, 6 gauge wire, carefully routed and secured), I still put a breaker all of 8 inches from the battery just in case...