I am not incompetent with dealing with electrical things but I lack some basic knowledge. I know that the gauge of a wire is it's thickness and it makes sense that if something is using 18 gauge all the way through and you splice in a 12 gauge, it might act as a fuse and fry, but how do you know what gauge to use for what application? Is it bad to use a much bigger gauge when extending a specific wire? What is a good gauge to go with when drawing power straight from the car battery? What about for grounds? Thanks!

 

http://the12volt.com/info/recwirsz.asp

 

For the most part, if you are extending a circuit and you know the what gauge it is ,you can go with bigger wire. The grounds should be the same as the B+ wires you are using since it carries the exact same load.

Got to know amps of what the circuit is going to draw when it is turned on.

The chart that Wabbit is refering to is a very good referance to go by with.
good luck

 

In specific, I have an 18 gauge ground wire that I am extending about 12 inches. All I could find was some thick 12 gauge copper wire and ring/butt connectors that fit it. Being a ground, is this a problem? I'm not sure what B+ means.

 

If that's all you have it will do, it's a bit overkill though.

B+ means Battery positive . Both positive and negative wires in any circuit should be sized large enough to handle the total amp draw of that load.

 

if you are adding it just a foot, some 18 gauge wire shouldnt be a problem. 12 is way overkill. take a look at that chart. i always like to add an extra 10% of amperage draw just to be on the safe side. what exactly are you running? what is the load it puts on the battery amperage wise?

 

Come on guys it's a ground, Not a current carring conductor. The positive is important for sizeing for the amperage, the neutral could be sized one gauge lower (depending on the controlled circuit), and the ground could be a 500 MCM if you wanted (good luck finding a crimp end in that size). In any event the circuit will only hold what the fuse or circuit breaker will put out, so over sizing will give you added protection. Now under sizeing the current carring gauge wire, well that's just asking for trouble.

 

Personally I would not comprimise on the neg. wire gauge, the added resistance in too of a small wire can cause the circuit not to fucntion 100% and can add problems that will be hard to find.

 

Remember, the negative (or common, but 'neutral' is AC specific) always carries just as much current as the positive, since it's all one closed circuit.

I'd be more worried about being able to afford a hydraulic crimper for it...

 

dz, your right. I spend way too much time on distribution centers. DC would be the "common" and should be sized the same. I am correct on the ground and over sizeing though. Oh and if you need a hydraulic crimper I could set you up. Pretty sure 500 is at about $14.50 per foot, so it may not be cost effective.

 

if I never have to pick up a 500 cable in my life I'll be perfectly happy... the 50' 4/0 cables we use for load banking are bad enough to deal with.

 

Nice to see another "gen set" man onboard, oh and drguitarum2005 sorry about the tread deviation. Use your 12 ga for your ground you'll be fine.

 

ya, you need to use the same size ground as your positive. the same amount of current will go through both wires, just a different polarity.

while we're on the story of amps....

at my school we have many truck-size diesel engines. one in particular is a detroit series 60 12 liter inline six. it takes about 700 amps to turn this motor over. as anybody in the electrical field might know, the slower a motor is going (due to more resistance) the more amps it's going to pull. so if you have an engine with weak batteries and it wont turn the motor over at all, you are actually pulling over a thousand amps if you have a big enough battery. we were doing this at school. i had this battery trying to start the engine that was discharged. so when you hit the start button, it would pull so many amps that the main battery leads (size 0/2) would actually straighten out because there were so many amps going thru the wire