The Point of Fuses

[mena661]

Fuses are to protect wiring, correct? If that is really so then I have a question posed as an example. Suppose I have a 55 amp converter. It is connected to a bank of batteries with 4 ft of #4 wire. ~180 amps is the max rating for 105C #4 wiring. What would be the point of fusing this wire if a catastrophic failure of the unit only sends a max of 55 amps down the wire?

[tvman44]

Also protects the converter from overload as well as everything. 🙂

[mena661]

MEXICOWANDERER wrote:
What happens if the converter gets mad, and I mean really REALLY mad at you and throws a hissy fit? A direct short with 4AWG is awful, like battery exploding time. Yeah fuses are a pain but what they may protect against is infinitely worse. Remember, Kelly said Murphy was an optimist...

So in this case, you're saying that there could be more than 55 amps drawn on a 55 amp converter? If this is the case, then I finally understand.

[mena661]

MNtundraRet wrote:
The fuse is protecting from shorts on a circuit. Worn or cut insulation on a cable. A loose connection sparking.

A short could only draw max amps from the device or devices on that circuit right? Then wouldn't just having adequately sized wiring do the trick? The amp draw won't be forever, the device will fail eventually. I guess I'm just not getting this. I can see the point of a circuit breaker on a 120V circuit cause you can have many devices that can draw more than the wire rating. I can also see protecting inadequately sized wiring (which is common in RV's). But if I have big honking wire, it's not going to melt with a current draw under it's rating. At least I don't think it would but that's why I'm asking.

[MEXICOWANDERER]

What happens if the converter gets mad, and I mean really REALLY mad at you and throws a hissy fit? A direct short with 4AWG is awful, like battery exploding time. Yeah fuses are a pain but what they may protect against is infinitely worse. Remember, Kelly said Murphy was an optimist...

[MNtundraRet]

The fuse is protecting from shorts on a circuit. Worn or cut insulation on a cable. A loose connection sparking.

[mena661]

Francesca Knowles wrote:
I always thought fuses protected everything on the circuit, not just the wiring.

That very well could be the case but I'm told different. Hopefully someone will weigh in on this.

[Francesca_Knowl]

I always thought fuses protected everything on the circuit, not just the wiring. But I know less than nothing about electricity so will await the experts' answers to this question with much interest.