my e-fan (temp and future aux) is wired with what i consider inadequately gauged wire. it appears to be 14-16 gauge (havent looked too far into it). i know that the fan draws around 15-20 amps consistently. it is protected by a fuse, which blew today (15amps). i want to reqire it and just need to know what gauge wire is good for 25 amps or around that.


thanks
-jeff

 

also, i did check the AWG load limits, and 14 gauge can carry 28amps, but the wiring gets very hot when the fan is on.

 

Here's how it goes for residentual wiring:

14 ga - 15 amp
12 ga - 20 amp
10 ga - 30 amp

I'll have to let the automotive experts reply on this un. The above is probably a bit much on the conservative side for an automobile.

 

That's the general rule for house wiring. Automotive wire is stranded and not solid so it can carry a higher current. Also, the length of wiring in a car is shorter than in a home, 5' to 20' versus 30' tp 100'.

 

If the wire is hot from running--not from engine heat-- then it is too small. It doesn't hurt to go larger. You can determine what size you have now by using a stripper with multiple grooves. The groove that the wire fills will be marked accordingly. I would start 2 sizes larger (#10 ) that what you have, then adjust again if necessary.
As previously stated, residental/comercial wiring is #10=30amps. Solid or stranded is the same. I have noted that auto wiring seems to be smaller than expected sometimes. Check your connections. Loose or poor connections will cause excess heat also.

 

It's not just a general rule, it's by the code book for industrial, commercial, institutional, and residential wiring. Also, stranded and solid wire are no different when it comes to current capacities. And lastly, overall length causes voltage drop, not current drop.

 

Nice chart on this page has lots of detail for a BUNCH of size wiring.

http://www.powerstream.com/Wire_Size.htm

 

Given a constant power demand the solid wire, due to its higher resistance, will have to flow more current due to the fact that there is a slightly higher votage drop across the conductor.

Code books just don't specify the guage of the wire and current load. The length of the wire plays a vital role into the proper gauge of wire that is needed.

 

all connections were redone before i drove it on the last highway drive...that's when i dropped the fuse to 15 amps just in case **** got too hot. they're all space connectors wrapped in heat shrink wrap. they will be soldered now.


anyway, i'll rewire it with 10G this weekend and hope for the best with a 25A fuse.

 

if you need to know what size wire we run for a 25 amp load it would be #10.. 12 is good for 20 amps and 10 (next larger wire) is good for 30-i see # 20 amp circuts in panels pulling 28 amps before they blow.. we rate them at 80%---so 80% of a 30 amp circut is 24 amps..in other words we make sure that the load isnt gonna draw more than 24 amps on a 30 amp breaker---------------16 amps is 80% of a 20 amp breaker,,,like i said you can pull more before it tripps depends on the breaker manufacture,,square d ''q o'' will trip out right away-----on the pooisite end of the spectrum federal pacific wont blow!!!square d are the more expensive but ther one of the best,,,fuses on the other hand are more protective they melt so are in essience safer,,i doubt if you could pull 28 amps off a fused 20 amp circut

 

Here is another chart.



But it never hurts to go 1 size bigger on the wire and fuse it properly for the amperage draw.

Codes always give minimum wire sizes.

 

also depends on what your feeding. i like to upsize 1 wire size when feeding a/c condensing units.. a 2 1/2 ton unit that gets a 2 pole 30 i d rather feed with # 8 because of the huge draw upon start up,, amp probe will peg, then level of to 6 amps per leg running but 300% upon start up,,cheap asses use min wire sizes on the tag of the side of the unit,,and when start up comes the wires snap in the pipe!!

 

I think he is just feeding an electrical cooling fan.

As you can tell in the chart, it has been adjusted for automotive use only, the cable length is a dead giveaway.

 

We need to know how long the wire is.

Ah...electricity...what a shocking feature.

The gauge of the wire is a measure of the diameter of the wire. Nearly all of the wire in use today is made of copper, including our vettes and any wire you will get for replacement unless it's some special wire that you don't want. The gauge of a wire is not the only determining factor for the current that can flow through it...length is also a factor because the limiting factor is the resistance of the wire. The resistance of a wire is Rho *L/A which is the resistivity (Rho) times the length divided by the cross-sectional area of the wire. The cross-sectional area is Pi * R^2 which is 3.1416 times the square of the wire's radius. The resistivity of copper is about 55 * 10^-9 Ohms * ft.

The resistance of a copper wire of a certain gage is usually available as an Ohms per foot specification…I notice that the table on the link above is in Ohms per 1000 feet.

Now...what we are REALLY concerned about here is not just how much current is passing through a wire, but how much resistance is in the wire when that current is passing through it. This is because the wire will produce heat in the range of R*I^2 which is the resistance times the square of the current. If we increase the current then it will increase the heat produced by the square of the current. And, if we increase the resistance (longer wire or smaller gage wire) then this will also increase the heat.

Based on the chart and experience I would say that the wire you can use is a 16 gage as long as it is not any longer than 5 feet. But, since you are saying that it's getting too hot with a 14 then it sounds like your wire is longer than 5 feet. If a 5 foot 16 gage wire carries 25 amps then it will create 12.3 Watts of heat. This appears to be the ball-park peak wattage for the chart in the previous post. I won’t know exactly if this is OK unless I can see the manufacturer specs for the wire to see how much heat it can dissipate. Personally, I would not want to see any more than 5 Watts of heat coming from a wire.
If you want to play around with my spreadsheet then you can download it from here (You will have to change the extension to xls because that server always turns file extensions to .doc for some reason):

Wire Heat Calculator

To use...change the highlighted parameters for length and amps and then look down the right column to see what the wattage is for the heat generated until you find something that will generate less than 15 watts and you should be fine...again this is just based on that chart.

 

very well stated

 

Another interactive chart I had saved to a computer at work.

http://www.geocities.com/CapeCanaveral/Lab/9643/awg.htm

 

ok, new question!


i pulled apart all of the wiring, and it appears that the temp sensing relay is all wired up correctly (albeit such that the fan comes on at what appears to be 100F...it's a desert so who cares?), however, the leads running to the fan are smaller (spade connected) after the original leads run out...as in 12 gauge out of the relay, switched to 14/16 ga after. when the fan runs, those connections getvery hot (as expected), but i also feel significant warmth from the relay's leads (the 12 ga portion of the setup), and most significantly from the fuse connection (flat type). will the restriction downstream cause heat upstream? or do i need to rewire with a new relay?


if option 2, please point me to such a relay.

 

also, since i'm no wiring guru, will a shrink wrapped butt-type connector be a good enough connection, or is there another, better way?

 

A great resource for automotive electrical and wiring is MAD Enterprises (www.madelectrical.com). The tech articles on the site and his tech book are very good.

Phil

 

thanks! that site has a lot of great info and will be very useful! however, it doesnt really answer the question about heat upstream from the restriction.