I need to add one more power outlet to my garage. The wiring for the existing ones uses 14-2 gauge solid wire. I have an entire role of this, worth of $60 which I don't entirely need but I bought it this way because I thought I would, and it was cheaper by meter/feet than buying exactly what I needed. Later on I discovered that I could buy "primary wire" (auto cable, seems to be stranded) for a much lower price.

What I need to know is what would be wrong if:

  • I use auto primary cable instead of 14-2 gauge
  • I mix the two (connect the stranded to non stranded)

In terms of intended purpose, the power outlet would be used to connect power tools if I need to work around my garage or if I need to work on my car.


I would extend the circuit for the additional outlet using approved mains wiring. Being that the existing uses 14 awg wire use the same type to hook up the new outlet. The cost of the correct style of wire will not be that great.

AC mains wiring has agency approved style insulation on the wiring designed to properly stand up to the voltage and abrasion tolerance needed for the application. Typical automotive wiring may not meet these requirements. I do hope that your existing 14-2 wiring is actually 14-2/wGND.

Another consideration is that the solid mains style wiring works much better under the screw terminals on switches and outlets than stranded wire. In automotive application the stranded wire is used because it is more flexible and works very well with crimp style terminals.

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  • Yes it is 14-2 with GND (three wires) As far as the cost goes you pay $52 for 70ft or something like that and you pay $25 for 15ft. This is a rip off but it is also off topic here :-) . – MiniMe Oct 3 '15 at 13:21
  • You must be looking at wire prices from a local neighborhood hardware store. Trip on over to a Home Depot. On line they show 14-2 NM-B w/GND in 250 foot roll for about $35. The 15 foot roll of same is $6.47. – Michael Karas Oct 3 '15 at 13:43
  • Try the Canadian stores :-) It is $59 homedepot.ca/product/… 10M (~30ft) is half of that . Sucks big time homedepot.ca/product/… – MiniMe Oct 3 '15 at 13:54
  • From what I saw the link you showed was for a 75 meter roll (246 ft). At the same .ca site there is the same style of wire 14/2 NMD90 w/GND available in 5 meter roll (16.4 feet) for $12.07. So not as bad. homedepot.ca/product/… – Michael Karas Oct 3 '15 at 14:05
  • You should be able to buy the cable by the foot, too, if you don't need a whole roll. The approved cable also has an appropriate fire rating for the application. It's all fun and games until you're trying to crawl out of a burning building with acidic smoke from the wrong kind of wire insulation burning your eyes and blinding you. Which is another issue. if the cable is going to be exposed at all (rather than closed up inside the walls), double-check your local code to make sure you aren't actually required to use conduit or armored/MC cable. – Craig Oct 4 '15 at 7:14

There are really two qualities of wiring that are important:

  • Gauge of the wire determines the resistance of the wire and therefore how much it will heat up with large currents. So you need to use a larger gauge wire when dealign with large currents to prevent the wire from overheating
  • The insulation of the wire has a number of important properties, probably the most important being its electrical insulation properties which prevents a spark from traveling through it. The insulation needs to be rated for the voltage traveling through it. Household electrical wire is rated up to 600V which is enough for anything you might have in a house or standard business. The insulation will usually have some additional ratings like heat tolerance, water- or UV-resistance, etc.

In the case of automotive wire you may get the gauge right but I would be concerned about the insulation. If it has the right ratings for your installation, go ahead. If not, spend a couple bucks and get wiring that will be safe. (Since it sounds like you're in Canada I will leave it up to you to identify the wire requirements, but in the USA you would want to use THHN/THWN rated cable for indoor installations).

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