Electrical fuse for 130 amp upgrade?

Alley Oop

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Dec 21, 2018

#1

• Dec 21, 2018

• #1

What amperage fuse should I use on the 4 gauge wire when upgrading to a 130 amp alternator?

 

Mustang5L5

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#2

• Dec 21, 2018

• #2

Fuse based on the wire size and lenght of run.

Did you use 60 or 90c wire? How long of a run?

 

Last edited: Dec 21, 2018

Alley Oop

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Dec 22, 2018

#3

• Dec 22, 2018

• #3

4 gauge about 7 feet long.

 

Mustang5L5

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#4

• Dec 22, 2018

• #4

120-125 amps. A circuit breaker would be ideal.

 

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Blown88GT

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Dec 22, 2018

#5

• Dec 22, 2018

• #5

Mustang5L5 said:

120-125 amps. A circuit breaker would be ideal.

Click to expand...

Keep in mind that circuit breakers must be de-rated from a fuse.
http://bdbreakers.com/breakersizing.php
You're only trying to protect the 4AWG wire from a short circuit in the alternator, placing a direct short across the battery.
This wire will not handle 500A for very long.
With no protection, a short circuit will melt the insulation & the copper & probably start a fire.
I'd stick with the fuse, 150A for the 130A 3G.

 

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Alley Oop

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#6

• Dec 22, 2018

• #6

Thanks for the input guys.

 

Mustang5L5

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#7

• Dec 22, 2018

• #7

I wouldn't go 150. Not in this application. 125 is already pushing it.

One thing that's never taken into consideration is ambient temp. Most wire load charts (such as in the NEC) are at 85*F, but underhood temps can reach much higher.

Just going up to 100 degrees you are at 90% of the rating with 90c wire and 80% with 60c. Go up even more and it keeps dropping off. Most audio grade 4g wire I've seen is the cheaper 60c wire. Get up to 120F and now you are at 60% rating with that stuff.


The amp rating charts on the net are all over the place as well. The NEC considers max ampacity of 4g 90c wire to be 95 amps at 85F. It's a tad conservative

 

Last edited: Dec 22, 2018

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Blown88GT

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#8

• Dec 22, 2018

• #8

You didn't read your own chart, degC, NOT degF.
That table is not applicable to DC current in engine spaces .
It's for AC conductors in a raceway with all kinds of caveats in the notes.

https://www.westmarine.com/WestAdvisor/Marine-Wire-Size-And-Ampacity
4AWG is rated for 136A.

As a former rocket scientist, I can tell you this is what you do & what works. I designed all kinds of DC power supply systems for DoD-DARPA.

 

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jrichker

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#9

• Dec 22, 2018

• #9

I am by no means a rocket scientist, but I can tell you that the insulation on the wire is going to be a limiting factor...

 

Mustang5L5

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#10

• Dec 22, 2018

• #10

Blown88GT said:

You didn't read your own chart, degC, NOT degF.
That table is not applicable to DC current in engine spaces .
It's for AC conductors in a raceway with all kinds of caveats in the notes.

https://www.westmarine.com/WestAdvisor/Marine-Wire-Size-And-Ampacity
4AWG is rated for 136A.

As a former rocket scientist, I can tell you this is what you do & what works. I designed all kinds of DC power supply systems for DoD-DARPA.

Click to expand...

You are right and I was incorrectly applying AC logic as that's what I'm most familiar with.

 

Last edited: Dec 22, 2018

Alley Oop

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Dec 23, 2018

#11

• Dec 23, 2018

• #11

I'm big on safety. I'll go with a quality 4 gauge wire and a quality 125 amp fuse. Thanks again.

 

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Blown88GT

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#12

• Dec 23, 2018

• #12

Alley Oop said:

I'm big on safety. I'll go with a quality 4 gauge wire and a quality 125 amp fuse. Thanks again.

Click to expand...

If you can find marine grade wire, it's usually the best. Some stereo shops use it, too.

I also want to point out that the 130A is not a continuous rating, but a peak or intermittent rating.
Just like gasoline engine horsepower can supply full power for less than 1 minute. Diesels somewhat closer to their rating.
Jet engines & rocket engines can put out full rated power for as long as there is fuel.

 

Blown88GT

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#13

• Dec 23, 2018

• #13

jrichker said:

I am by no means a rocket scientist, but I can tell you that the insulation on the wire is going to be a limiting factor...

Click to expand...

The chart is an excerpt from the standards for marine construction, American Boat & Yacht Council (ABYC), Std. E-11, Table IV-A, the marine equivalent of the NEC (National Electrical Code). The 160A is for 105degC rated insulation, which my marine grade wire is. It's printed on the insulation & the lugs were factory soldered.
https://www.paneltronics.com/atimo_s/news/E11Excerpts.pdf

 

jrichker

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#14

• Dec 23, 2018

• #14

I have

Blown88GT said:

The chart is an excerpt from the standards for marine construction, American Boat & Yacht Council (ABYC), Std. E-11, Table IV-A, the marine equivalent of the NEC (National Electrical Code). The 160A is for 105degC rated insulation, which my marine grade wire is. It's printed on the insulation & the lugs were factory soldered.
https://www.paneltronics.com/atimo_s/news/E11Excerpts.pdf

Click to expand...

I have never worked on rockets or boats; only aircraft and automobiles, so those are boundaries of my experience with things that move under their own power.

 

JD1964

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#15

• Dec 25, 2018

• #15

Alley Oop said:

4 gauge about 7 feet long.

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Just curious your routing that required a 7' cable. Mine was like that when I ran it over the the radiator support on a previous installation. I later re-routed the cable running it underneath along K member. The new cable including the fuse block and extension from it was less the 4' in length. The shorter cable will perform better with less amp loss at the load side.

 

Alley Oop

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Dec 26, 2018

#16

• Dec 26, 2018

• #16

John Dirks Jr said:

Just curious your routing that required a 7' cable. Mine was like that when I ran it over the the radiator support on a previous installation. I later re-routed the cable running it underneath along K member. The new cable including the fuse block and extension from it was less the 4' in length. The shorter cable will perform better with less amp loss at the load side.

Click to expand...

John, it was just a guesstimate based on what I had read. When I get to the point of installation, I will try to make the route as short as possible.

 

Blown88GT

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#17

• Dec 27, 2018

• #17

My battery is relocated to the passenger side because the SC is on the driver's side. This necessitates a longer cable to the starter relay but a much shorter one from the alternator to the battery. Replacement battery was changed from group 58 to group 59, which is a bit larger. Battery to fuse to alternator cables & fuse had to be re-routed. One cable now goes on top of the battery instead of the side.