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Wire sizes and Fusing
#1
Information 
Wire Sizes and Fusing: 

There is a maximum amount of current that each size wire can carry safely before suffering either long term, or in some cases RAPID deterioration.

The technical term for this is its AMPACITY, which is a made-up term from the two words Ampere Capacity.

In addition to wire size, it is also partially dependent on the temperature rating of the insulation on the wire.  Wire with insulation rated for 90 degrees Celsius has a higher ampacity rating than the same size wire with insulation rated for 60 degrees Celsius does.  Bundling a bunch of wires together calls for derating the ampacity, because the wires in the center of the bundle can’t shed heat like they could if they were run singly.

Anyway here’s a simple table of fuse sizes matched to wire gauge size that’s close enough for government work, as they say.

For 14 gauge wire, it’s 15 amps
For 12 gauge wire it’s 20 amps
For 10 gauge wire it’s 30 amps
For 8 gauge wire it’s 50 amps
For 6 gauge wire it’s 80 amps
For 4 gauge wire it’s 125 amps
For 2 gauge wire it’s 200 amps
For 1 gauge wire, it’s 250 amps
For 1/0 gauge wire it’s 325 amps
For 2/0 gauge wire it’s 400 amps

You can ALWAYS put a smaller fuse on a wire safely.  For instance, If I were installing a fuse block for my house circuits, and it was rated for a maximum of 100 amps, I would run 4 gauge wire(125 amps) from the battery to the fuse block, and fuse it close to the battery with a 100 amp fuse.
Regards
John

Life is not about discovering yourself.  Life is about creating yourself!

Talk is cheap because of simple economics: The supply FAR exceeds the demand!
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#2
Good post , I'd only add that the longer the wire , the less amps it will pass without heating up .
Stay Tuned
popeye

Weirdo Overlord  YARC CRVL edition
12 "Stinkin'Badges"  a "Full Monty Badge" 2 "Just Ignore Me" clusters  4 "Pine Cone" clusters  one "Stinkin' Badger" and 4 of the coveted "Flying Manure Spreader"awards! (What a "Stinkin' " honor !) + ROOIRIA
 

1981 Travelcraft Class C - 23'
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#3
Also the type of wire also makes a difference.  Aluminum wire is inferior to copper wire, and has a tendency to compress at the point where it is clamped.  When I had my house, I had to tighten the wires going to the AC system from the fuse box twice a year to keep it operating properly.  

Spend the extra money and buy copper.
Trouble rather a tiger in his lair than a sage at his books. To you kingdoms and armies are mighty and enduring, to him they are toys of the moment, to be overturned with the flick of a finger. G Dickson.
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#4
(05-29-2015, 11:59 AM)rvpopeye Wrote: Good post , I'd only add that the longer the wire , the less amps it will pass without heating up .

Yeah, voltage drop calculations probably deserve a separate post.  Thing is, I hardly ever worry about them, I just over-engineer the wiring myself.

Regards
John
Regards
John

Life is not about discovering yourself.  Life is about creating yourself!

Talk is cheap because of simple economics: The supply FAR exceeds the demand!
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#5
I was thinking about that after I posted.
In a small (under 25') vehicle , those sizes should be just fine.

I bought a big spool of 10GA and just use it for everything, double and triple for heavier loads......
Stay Tuned
popeye

Weirdo Overlord  YARC CRVL edition
12 "Stinkin'Badges"  a "Full Monty Badge" 2 "Just Ignore Me" clusters  4 "Pine Cone" clusters  one "Stinkin' Badger" and 4 of the coveted "Flying Manure Spreader"awards! (What a "Stinkin' " honor !) + ROOIRIA
 

1981 Travelcraft Class C - 23'
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#6
The temperature the insulation is rated at also matters -- I think that table is for the most common 90C rated wire, 75C wire needs smaller fuses. If packed tightly, it needs to be derated. The voltage drop is usually more concern on 12v wiring, and that is lenght sensitive.
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#7
(05-29-2015, 03:22 PM)blars Wrote: The temperature the insulation is rated at also matters -- I think that table is for the most common 90C rated wire, 75C wire needs smaller fuses.  If packed tightly, it needs to be derated.  The voltage drop is usually more concern on 12v wiring, and that is lenght sensitive.

blars, if you feel these are way off, please feel free to post different figures, and your reasons for recommending them.  I don't mind.  I long ago (reluctantly) renounced all claims of infallibility, though it IS making it harder to pick up chicks.

Seriously, I cribbed these figures years ago from an audio site, and these are apparently - for better or worse - what they use when doing installations.  I've never had a problem with them, but that could just be dumb luck.

Regards
John
Regards
John

Life is not about discovering yourself.  Life is about creating yourself!

Talk is cheap because of simple economics: The supply FAR exceeds the demand!
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#8
somewhere I have a table for wire size vs length for amp rating for 12v DC. however I can't find it at the moment. I really need to clean up my favorites. highdesertranger
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#9
So what wire sizes do you use for typical vandwelling installations?
2015 GMC Savannah 2500 van, 480 watts of Solar Panels--and a wonderful furry best friend named Cody. I'm out to change the world!
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#10
I used this calculator for sizing my 12 volt system wires.  Gives correct wire (to ABYC standards) for both ampacity and voltage drop.

http://circuitwizard.bluesea.com/#

For fuses, MaineSail had recommended the largest fuse for wire size (in 12V systems) to minimize voltage drop across the fuse.

http://www.pbase.com/mainecruising/fuse_voltage_drop
http://www.bdfuses.com/fusesnwires.php

-- Spiff
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