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Discussion Starter #1 (Edited)
Since I'm working through my defroster load issue and figuring out what gauge of wire is needed for the application, I thought I would put up a sticky which shows various 'opinions'.

Opinions? you might wonder what I'm talking about. Isn't it set in stone?

Yes and No. For most 'non-critical' applications, most suppliers use a thinner gauge (larger number) wire since it's:

a. Cheaper
b. Lighter
c. Easier to work with

Unfortunately, a thinner gauge typically has an higher resistance to the flow of electricity. So that's bad right?

Not necessarily. If the application doesn't need that much power or the absolute voltage level isn't critical, then it doesn't really matter. However, if there is a lot of current draw, a drop in voltage will be seen and in certain applications that drop will also mean a drop in performance. The drop in voltage can be substantial...

Here's a snap shot of a wiring gauge table from a website that specializes in offroading -

Capture.jpg

The table is fairly easy to understand as you pick the current you are running on the left hand side and then distance you are running that on the top and wham! you have your gauge of wire. For example, 10A for 10 feet is 18 gauge.

Now if you look at the following table from a marine boating company -



You'll notice that they start talking about voltage drops and non-critical applications.... If we take that example from above, 10 A for 10 feet, in this table, we see that it's points to 14 gauge with only a small drop in voltage. 18 gauge isn't even listed in the table! According to the above table, the voltage drop using 18 gauge for 10A for 10 feet may be greater than 10% so in a standard 12V circuit, you'll really see approx 10.8V coming out the other side at 10A. If you used 14 gauge in the same application, the drop will be 0.36V or 11.64V. If you increase the gauge to 12 gauge or less, you'll see an even lower drop in voltage at a given current draw.

So what does that mean? If you are running lights, lights will generally be brighter the higher the voltage so just by going to 14 gauge cable instead of 18, you may see an appreciable increase in brightness.
 

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Um, okay so I've read your post 3 times now so excuse my ignorance.
I don't think you've actually asked what you want us to comment on, other than: "What gauge (AWG) of wire should I use?"

Perhaps we can start with the power and distance you're working with?

What I know:
- Rear defroster project (based on various threads)
- Voltage is 12-14V... are we going on 12V standard voltage, or 14V with the alternator and car running?
- What amperage are we looking at here?
- What distance have we determined the cable to be?
- Have you found a good grounding point already? (ie. Can we disregard this part of the equation?)

In your example above, and because the defroster is such an interesting project, I'd go with the 14awg cable. Why? It has the least drop in power for you and the cable still really isn't that thick. Why not just get the better cable and avoid questions later whether a thicker gauge would have improved its performance? If we're really curious about its performance with various voltage drops, it'll be easy enough to add a potentiometer near the end to vary its resistance, but you can't decrease the voltage drop if you're already maxed out at a cable's potential.

The cost of cabling is relatively minor considering all the upgrades/etc you do to your XV. This way, you can confidently say that you did a great job on upgrading the defroster and not just a "good enough" job.
 

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On a high wattage draw application like a resistance heater (defroster) I'd actually go a bit overboard and use a wire gauge that potentially had no current or voltage loss. The wire cost is negligible, the performance improvement could be dramatic.
 

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Discussion Starter #4
Um, okay so I've read your post 3 times now so excuse my ignorance.
I don't think you've actually asked what you want us to comment on, other than: "What gauge (AWG) of wire should I use?"

Perhaps we can start with the power and distance you're working with?

What I know:
- Rear defroster project (based on various threads)
- Voltage is 12-14V... are we going on 12V standard voltage, or 14V with the alternator and car running?
- What amperage are we looking at here?
- What distance have we determined the cable to be?
- Have you found a good grounding point already? (ie. Can we disregard this part of the equation?)

In your example above, and because the defroster is such an interesting project, I'd go with the 14awg cable. Why? It has the least drop in power for you and the cable still really isn't that thick. Why not just get the better cable and avoid questions later whether a thicker gauge would have improved its performance? If we're really curious about its performance with various voltage drops, it'll be easy enough to add a potentiometer near the end to vary its resistance, but you can't decrease the voltage drop if you're already maxed out at a cable's potential.

The cost of cabling is relatively minor considering all the upgrades/etc you do to your XV. This way, you can confidently say that you did a great job on upgrading the defroster and not just a "good enough" job.
Actually, I'm not really asking for comments here. This post is a sticky for reference when people are installing electrical devices! That's why I didn't reference the defroster project in this thread because it doesn't belong in this thread... it belongs in the defroster thread.
 

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Discussion Starter #5
On a high wattage draw application like a resistance heater (defroster) I'd actually go a bit overboard and use a wire gauge that potentially had no current or voltage loss. The wire cost is negligible, the performance improvement could be dramatic.
Yep, that's the purpose of the post to guide people who might be wondering (or following bad advice on the web) to use the bigger gauge wire instead.

And for the record, I'm looking at 10 gauge.
 

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I stand corrected - thanks for clarifying. That 10 gauge wire sounds even better.

Why run just 1 wire when you can run 2 wires? Serious thought though, while anybody (else) is running wire, it could save trouble if you run wiring for other projects at the same time. I plan on running several sets all at once so I won't have to do it all separately... yay for efficiency? :)
 

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Discussion Starter #7
I stand corrected - thanks for clarifying. That 10 gauge wire sounds even better.

Why run just 1 wire when you can run 2 wires? Serious thought though, while anybody (else) is running wire, it could save trouble if you run wiring for other projects at the same time. I plan on running several sets all at once so I won't have to do it all separately... yay for efficiency? :)
That's what I always do. I would love to find 10 gauge zip/lamp cord. It's a lot easier to run two wires if they are connected together to start with!
 

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There's a bunch of stuff on eBay and online, but not sure how easy it is to find locally. How about 10awg zipped speaker wire? May be easier to find... ;)
 

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Two options for 10 AWG are: SJE (SJ) portable power cable for making extension cords, comes in 2 and 3 conductor in one jacket & THHN cable is single conductors with teflon insulation that get run inside conduit pipe but is not as flexible.
 

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Discussion Starter #10

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The table is fairly easy to understand as you pick the current you are running on the left hand side and then distance you are running that on the top and wham! you have your gauge of wire.
I love this table. It also reinforces the idea of keeping your wire runs shorter, so having wires zigzagging back and forth between the front bumper and the interior is a bad thing if it can be avoided. Placing that new relay in a central location can help, too. Being smart about how you lay out the wire can be as important as the wire you select. Of course, you do always have the option of overbuying, such as using 14-AWG or 12-AWG instead of using 16-AWG as your project default.
 
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