Electrical question/opinions

What is the amp limit to safely run through 12 g. wire?

 

Dig that graph. I need that on the wall for a quick reference.

 

That chart is really cool! I can't tell you how many times I wondered what wire to use in a given application.

Thanx,

 

This applies to any voltage value. Wire size is determined by amps and distance. 12 volts, 440 volts, AC, DC, positive, ground all same/same.

 

Usually 20 amps for 12 gauge

The chart is not very helpful, really.

 

The chart is actually very helpful. As you can see by the chart 20 gauge is acceptable for 12 gauge up to 13 feet as you have stated. For shorter runs it can handle up to 35 amps. If one chart is not good enough then here is another from a different source. If you do the math based on a given wire gauge resistance per foot you will come to a similar conclusion.

 

The National Electrical Code calls for a 20 amp circuit breaker on 12awg wire in home circuits. The code lists the ampacity of the wire at higher levels but it depends on the insulation.

http://www.lappusa.com/14030.16description.htm

 

like I said, it's not too helpful for someone who's just trying to wire up a car.

Standard practice is to use 30 amp fuse on 10 gage, 20 amp on 12 gage, 15 amp on 14 gage, 10 amp on 16 gage. That's really all you want to know.

I understand about the lengths, resistance, temperature, etc all play a role, but seriously, why make it complicated?

 

The question was "What is the amp limit to safely run through 12 g. wire?" not what size fuse it it would take to protect the circuit. These are two different issues.Even fuses are rated differently depending on the usage ..for instance slow blow and fast blow fuses. The question was very simple and the chart gives the very simple answer as to what a particular gauge wire can safely handle.

 

Why use underrated wire? Is there something wrong with using an over rated wire size for everything? Don't use the cost copout, the car and my house are worth saving. Bob

 

I agree...That's why the chart is so handy.You can see what the max rating is for a particular wire gauge and length and then make the decision as to what gauge wire will work best for your needs . Make sense to me.

 

For those who are interested in knowing more about fuses here is some very good and easy to understand information.

 

I got the information I needed. I've been doing this stuff a long time but you are never too old to learn something. I had my electric fan wired with 12 gauge, the wires coming out of the fan are 14g so I figured I was a size bigger. But the fan was blowing 20 amp fuses to start (and 25s). I put an amp gauge on and it spikes to almost 50 amps for a split second on start up and then settles down to 17-18 amps pull. Hot side is about 4 foot run and the cold side with the relay is maybe 5 foot. I changed the fuse out for a 25 amp breaker, probably a little too much for 12g, might warm up a wire before it trips

 

http://www.jalopyjournal.com/forum/album.php?albumid=35656&pictureid=409696

I got this from Thunder Roads Electrical Guide by Bill Sinclair.

 

I disagree. The distance you can safely go with a given gauge of wire is going to depend on voltage drop and while 2V drop on 120V system isn't a big deal, it would be huge on a 6V or 12V system.

 

Thanks for the chart !!!

4TTRUK

 

I'm with Squirrel.

 

50 amps is one hell of a momentary draw. Hard to imagine. Something's not right-I'd suggest checking with the manufacturer. Next you'll be stuffing a penny into the fuse holder.

 

50 amps for a momentary draw isn't surprising. Motors can draw a LOT of current when they start, especially if they have to get something spinning.

Sounds like the fan wiring problem is fixed properly.

 

A penny? What kind of fuse box does your car have?

 

yeah...everyone knows you wrap a gum wrapper around the fuses in an old car

 

It was a joke, son. Back in the day, people would stick a penny when they didn't have a fuse, into the fuse holders in their house often resulting in a serious fire. Of course, now that pennies aren't really made of copper, it doesn't work so well, plus most of us have circuit breakers in our homes.

My car has two fuse panels-one uses the traditional gl*** tube fuses, the other the newer spade/blade fuses. I considered getting auto reset circuit breakers for that one, but it rarely blows a fuse and I have a lot of fuses .

 

I'd be looking into that fan as well. I agree that motors draw extra upon startup, but it is done in milliseconds and takes a pretty sophisticated tester to capture it - you have to specifically look for it. If you are looking at a gage or digital meter and it shows 50a draw and then backs off as the fan gets to running and it is a single fan running at 17-18a then i would be very su****ious of what is going on. You've been here a long time and if this is the first time yo have heard of it right? If that was normal then there'd be lots of posts about what size fuse do i...
I regularly hook up dual fans, gen 12" or maybe 14" if i can stuff 2 of them in there, i like spal and deraille, i've hooked up most every fan ever made and none of them have burned a 20a fuse and they are all on 20a circuits.

 

I tried that once. Had a new Econoline and everytime you used the cigsrette lighter with the dome lights on, it would blow the fuse. (don't ask what we were doing) All was fine until the lighter stuck in when I was going down the road and suddenly the interior was filled with wire fire smoke. It fried the hot wire from the lighter to the ignition switch, and everything it was touching. Never tried that trick again.

 

Cooling componets says use a 75 amp relay on their fan that I used in the coupe. Watch you amp gauge are volt meter when your fan kicks in. The amp draw on start is huge.

 

Please give something in the way of information about the chart.

 

With high amp starts curcut brakers are a better choice there based on load time.

 

I think this isn't really the question. Start this way.

1. What size load do I have?
2. What size wire do I need to have a voltage drop at the load I can live with? Also consider the allowable temperature rise of the wire you will use.
3. What size fuse do I need to protect that wire?


Blue Sea Systems (I have no connection to them at all) has great data on DC wiring. Here is a step by step full color chart on how to select wire and fuses:
http://bluesea.com/files/resources/reference/20010_Rev.003-web.pdf

 

Really?? You are telling me what I should ask?
!. I already knew the load

2. I also had determined what protection the circuit needed.

So all I needed to determine was if my 12 gauge wire was sufficient. I purposely worded the question so I could obtain the information I needed, not get schooled on how to design the system.