Is BCAE1 right about this one?

[Proximity 10+ year member]

I was reading through the fuses page and when it's talking about fusing with a distribution block it doesn't really seem like it makes sense and I'm looking for what others think.

http://bcae1.com/fuses.htm

Basically it says when you're reducing a wire size from a distro. block that it needs to be refused.

This is the diagram the used for the example:

It says wire C would not need to be fused because it's the same size as wire B (which the 125a fuse protects) but the 125a fuse would not protect wire D in the event of a short.

It seems to me like if there is a short, pretty much any reasonable fuse size would protect it as going by ohm's law if the positive wire come in contact with the frame it would pull thousands of amps, which any fuse would protect.

So the only fuse you would need is the 125a fuse as it would protect every single wire on the distribution block.

Am I wrong?

Click to read more...

 

[hornedfrog1985 5,000+ posts]

NVM, I'll just delete my post :/

 

[Proximity 10+ year member]

You probably don't want those smaller wires drawing 125 amps worth of current, melting, and so on. But eh, you gonna pay for fuses for all them wires?
I guess the question would be is, would the fuse fail before the smaller gauge wire fails?

Well I guess I'm implying that you're smart enough to not put those wires in a position where they're be subject to that kind of current. (again, except in a short where you'll be pulling way more amps that 125 anyway, so the fuse of the battery would protect it)

I guess there could be a situation where the amp malfunctions and somehow draws lots of current, but then the amp's fuse would blow. So I guess if your amp doesn't have a fuse then you'd want to fuse the wire out of a distribution block.

And yeah, that pretty much is my question.

 

[KyleBechtold 5,000+ posts]

the 125 a fuse is smaller than those main wires so it would go first.. when you reduce wire size they need a fuse to protect them.. therefor the other fuses.. the smaller wires would melt before that 125 went out

 

[KyleBechtold 5,000+ posts]

fuses on the wire aren't there to protect the equipment.. they are they to stop a fire.. from the wire melting if it started to short..

 

[Proximity 10+ year member]

fuses on the wire aren't there to protect the equipment.. they are they to stop a fire.. from the wire melting if it started to short..

I know, but if it was shorting it would be pulling more than 125 a anyway.

Or am I wrong about that?

Even if the end resistance is .01 ohms (which I'm guess it's usually less than that), using the 14.4 normal voltage, that's 1440A, more than enough to blow the original fuse.

 

[funkyab 10+ year member]

fuses on the wire aren't there to protect the equipment.. they are they to stop a fire.. from the wire melting if it started to short..

X1000000000!!! Some people are idiots and skimp out on the fuses. I used to do the same years ago until i started using more power. And my first experiences with greater power was on my boat and i sure as hell was not going to take ANY chances in an environment like that. Fuses fuses fuses for me.

 

[KyleBechtold 5,000+ posts]

I know, but if it was shorting it would be pulling more than 125 a anyway.

Or am I wrong about that?

Even if the end resistance is .01 ohms (which I'm guess it's usually less than that), using the 14.4 normal voltage, that's 1440A, more than enough to blow the original fuse.

Ok but only the max load of the smaller wire can be carried across that smaller wire.. it will try to pull all of it and melt it til it gets to the fuse..

 

[KyleBechtold 5,000+ posts]

get what im saying?

 

[IDSkoT 5,000+ posts]

The rule of thumb, for safety purposes is to refuse. But it's not necessarily needed. Like I said, just an added precaution. Like fusing the positive wire from your alternator to battery.

 

[IDSkoT 5,000+ posts]

the 125 a fuse is smaller than those main wires so it would go first.. when you reduce wire size they need a fuse to protect them.. therefor the other fuses.. the smaller wires would melt before that 125 went out

A wire will only take as much power as whatever on either end is needed. A fuse is to protect the wire if the wire becomes grounded and an excess of current is flowing through it, or if there's a backwards pull (forgot the name.)

The 125 ampere fuse is to protect the big wire.

The refuse is needed for the smaller wire since it cannot take 125 amperes at a constant rate.

 

[Rich B 5,000+ posts]

Distribution blocks are mounted just ahead of the amps, and some amps require an external fuse on their power wire because they dont have internal fuses

in them.

Older Zed made amps were like that.

Thats probably why that diagram shows fuses after the distribution block.

(If your amp has fuses on or in it, ignore that part part of the diagram.

 

[Cravingbass123]

OP, the answer is

balls

 

[Proximity 10+ year member]

get what im saying?

Yeah I know what you mean, but would there actually be a situation where that wire has a current that is large enough to melt the wire but not high enough to blow the 125a fuse?

 

[ultimate157 5,000+ posts]

That diagram is 100% correct. Reread it as many times as it takes to learn why. No need to try reexplaining it, everything is spelled out on that page.