current flow neg to pos?

This may be more of a question of hole theory vs electron flow theory.  While working on my AAS in Electronics technology i asked my instructors and never got a real good answer on this.  They taught electron flow theory.  The idea that current travles from -neg to +pos.  For the sake of this question lets just say that is true.  If that is true, then why do you fuse an amp in a car on the positive lead at the battery.  Allong that thinking, i would say it would make more scense to fuse the neg/ground wire of the amp.  Furthermore I have seen cars not been fused at all and in every case were i have ever seen that wire burn up, the burn starts at the positive terminal and works it burn back from there.  I did have one instructor say that it was because while travleing from neg to pos.  the spot at which the current would have had to travle the furthest was at the battery and therefore it would have the most voltage drop, and have to compensate with higher current there.  that kind of made sence since higher current will create higher heat, but why when you test with a meter, would that end of the lead alwais have higher voltage than the end of the lead at the amp, and isnt current supposed to be constant accross a circuit?  I just gave up on getting this answer from my instructors.  I took what they had to say, regurgitated it on the test and got my degree, but i still really whant to know the answer.  After reading some of the answers from many of the very well informed people on this site, i figure i would give this question a shot here.  

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If your cousin is such a good installer, and he will install anything for a 6 pack; why are you talking to me?

In simple terms it doesn't matter, but most systems can have multiple paths to "GND".
Also if a "hot" wire shorts to something, it will probably be ground - hence you fuse the hot side (since you can't fuse "that" GND point unless to fuse the whole lot).

Electrically it doesn't mater where you fuse it.


Also electricity doesn't have a direction of flow in reality - that is merely our primitive way of considering it - eg, a model where "conventional current" flows + to - thru the circuit (aka - to + thru the source - eg battery).

Electricity can be the migration of +ve charges - it isn't always "electronics" (ie, electrons going the other way).

[& IMO since nobody can define "electricity" as a quantity or fundumental unit, who cares?)

Conventionally, "electricity" flows from (+) to (-).

Electrons are what is moving and electrons are (-) charge.
So, In reality The (-) flows to (+).

I guess in a circuit, it doesn't matter. You need BOTH for anything to happen.

Fusing the GND wire would be fine for an amp as an example. But what happens if that (+) wire from the batt gets pinched by something and it shorts out? A fire thats what happens!
So as stated above, the fuse at the batt PROTECTS the wire too.


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The positive wire is fused because if you fuse the ground wire and you blow the fuse, the amp will seek ground via the Shield of the RCA cable.  This would be really bad if you have a Pioneer deck.

Positive wires are fused because the entire vehicle body is ground.  The fuse is there to protect the wiring against short circuits to ground. 

i do appreciate all of the answers, but i think i left out the most important part of what i was trying to ask.  If current is flowing from neg to pos.  then why does the wire burn up from pos to neg.  I am not talking about if the wire were to become pinched and grounding out.  i am talking about if the wire were to burn up from over current.  Like trying to draw 120a through an 8ga wire.

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If your cousin is such a good installer, and he will install anything for a 6 pack; why are you talking to me?

B/c the body of the car (ground) is less likely to burn up than the tiny wire (positive).

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2013 Kia Rio -90a alternator
DDX470HD GTO14001 GTO1014D (x3)
Big3 in 1/0G
1/0G to GTO14001

The only wire I've ever seen "burn up" in a car burnt from the point it was grounded all the way back to the battery. There was no indication it got any hotter near the battery.

I've seen wires burn close to the battery - this is typically caused by a poor connection between the wire and the battery.

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Kevin Pierson

You are over thinking this a little bit.
If the car was positive ground, the negative wire would burn from over current.
On the same note, if cables were attached to each terminal of the battery and short them together, both would heat up at the same rate.
In the case of a neg ground car, the neg side can handle much more capacity than the pos wire, hence the pos wire burns first.
On a practical level, it doesn't matter which direction "electricity" flows as long as you keep everything consistent.
Addressing the measured voltage between the 2 ends of a wire.
The near end has a higher voltage because of the resistivity of the wire and the fact that current is the same in a series circuit.
In order to to measure the same voltage at both ends the current would have to be higher at the far end, which is not practical.

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This information is provided only as a reference.
All circuits should be verified with a digital multi-meter prior to making any connections.

Resistance = heat.  If a wire has burnt at only one end of it, there is a bad connection at that point.

Funnily although I was taught pos to neg, it's obvious why you fuse the pos side, the car body on a modern vehicle is the ground thus any short circuits will affect the battery side thus fuse the battery side.
All the other points made above are practical and practical use is what it's all about, though I thought it was more to do with electron energy and spin rate.
Back in the day on the early car phones, we fused both pos and neg.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

Interesting seeing the various answers which IMO are variations of my reply, else misleading....
So, to paraphrase...

The polarity of the fuse has NOTHING to do with flow direction.
It is the HOT polarity that is fused for reasons give above.
EG - telcos often have positive ground/earth, hence their fuses are in the negative leg (ie, -ve is HOT). So to0 older English & other +ve chassis vehicles.     

"Conventional Current" (which is how we "picture" current) is the flow of positive charges from +ve to -ve (thru the circuit).


In reality, electricity is an "effect" and is NOT migrating electrons or particles.
VIZ - it can be any combination migrating electrons and -ve ions or particles one way, OR +ve ions or particles the other way. "Naked electrons" need not be involved.

And it is not the "movement" of electrons or particles per se - whereas electricity & e-mag travels at or near light speed, electrons only travel a few meters per second and other particles are normally slower.

Remember - we only "model" electricity....