Using two 14 AWG wires instead of one 12 AWG

Question

I do understand there are many factors when choosing what AWG wire, however by the charts, tools, and info I have found, using two 14 AWG copper wires should be equal to a single 8 AWG wire. 8.025 AWG to be really specific. Am I missing anything important? If I have several hundred feet of 14/2 with ground and 14/3 with ground, is there any technical problem with running a pair of them to replace the 12/2 or 12/3 that I try to use as a minimum, or should I toss the extra 14 AWG Romex as useless?

Answer 1

Electrically, multiple smaller wires in parallel act as one larger wire. At DC, it's strictly about conductor crossection area, assuming the same conducting material (usually copper) is used in all the wires. With AC, multiple separated wires are actually better than a single wire with the same crossection area.

However, if this is for line power, then your question becomes a legal issue, not a electrical one. I suspect that it's NOT allowed to parallel multiple smaller wires and then assume the whole is rated for the sum of the currents of each of the wires. I'm no expert on the electrical code, and it varies by jurisdiction anyway. You have to consult your local electrical code.

Answer 2

It depends where you're doing it. If it's a R/C airplane or drone, have fun. If it's marine, automotive, air or railroad, you have the respective government rules to follow (in the land of AWG and Romex, probably Coast Guard, SAE, FAA and FRA respectively, or your national rules largely cribbed from those rules).

Structures and RVs, you have to follow structural rules, and in North America that is (or is harmonized with) El NEC.

And now a regulatory hellstorm begins. These rules impact occupancy permits, insurance and mortgage. Fail to follow them and you need to disclose in seller representations. Also insurance won't pay and the loss is on you. Or you could be the dumb duck who started a multi-county wildfire. And since noncompliance is illegal, the loss is due to an illegal act meaning you can't escape the debt in bankruptcy.

Et cetera, et cetera. The accountability never ceases. No insurance company anywhere is going to let you stick them with the risk.

NEC's take on this is wire is cheap and you can trade "whatcha got" for "whatcha need" on Craigslist. No rule against used wire in good condition. I myself don't own any #14 since at the rate I might use #14, the "carrying cost" of owning multiple fractional spools of #14 is more costly than the incremental cost of using #12 where #14 would suffice. It also reduces weight and volume in my kit.

NEC prohibits paralleling in AC power unless you use equipment UL-listed for paralleling at the supply end, and 5 rules are met (one of which is minimum size #0 aka #1/0). So in practical terms owing to equipment costs, you're probably not going to use it smaller than 500-600 amps. Larger wire is cheaper than parallel-approved source equipment. However power companies dance to different rules, and you might see paralleling on the utility side of the meter.

There is a marginal benefit to paralleling because of skin surface area. When you double wire diameter you quadruple cross section, which affects voltage drop, but you only double skin surface, which limits cooling. That's why in the ampacity tables NEC 310.15(B)(16), 2x the cross-section isn't 2x the amperage. So paralleling helps by adding skin surface. However, this is undone when you throw all the wires into a conduit, because the conduit skin becomes the limiting factor. See NEC 310.15(B)(3)(a).

That said, I don't see any problem doing it for low-voltage distribution where the feeder has fuse protection lower than the ampacity of the smallest wire. This is where you often see monstrous voltage drop problems, and you have no obligation to carry a safety ground since system voltages are low. I have seen 12V solar and hydro installations where there was considerable distance, the project failed because the installer wasn't willing to spend any more money than #8 copper (on a 20A run). Well, you can get 2-2-2-4 aluminum MH feeder for about the same cost per foot/meter, and their project absolutely would have succeeded if they were paralleling that.

Answer 3

This answer addresses some of the side issues that you raised in your comments:

15 amp breaker or not, 12 AWG wire is the smallest wire I will use.

There was a time when I felt the same way. However, after doing some extensive rewiring of some older houses, I've changed my mind. AWG 12 is much more difficult to work with in tight spaces such as junction and outlet/switch boxes, and I find that it just isn't worth the trouble.

Due to factors like resistance buying a thinker gauge wire will always pay for itself on your power bill.

How do you figure that? For most types of loads, if you deliver higher voltage to the point of the load, the current draw — and your power bill — will increase.

The only type of load for which this isn't true is a "constant power" load, such as anything that uses a switching regulator. In this case, delivering higher voltage will result in lower current. The problem is that this type of load is an insigificant fraction of your total load in most cases.

In this case where I am building something that is not a house the code does not apply.

It doesn't matter whether you're building a house; the electrical code applies to anything that is permanently wired to the electric utility, or to a local generator.

Answer 4

In house or building wiring, or anything that is connected to power,

14 AWG wire has to be protected by a 15A fuse. #12 AWG is protected by a 20A fuse.

Doubling #14, 12, 10, 8, ......wire to increase ampacity is not allowed. Doubling is allowed for much larger sizes. The #14 AWG Romex is not useless, keep it for any circuit that will be protected with 15A fuse. An exception is where the voltage drop is more than 5% ( extra long runs with high load), or exposed to high temperature. Then use #12 for 15A circuits. If you don't want the #14 Romex, sell it and then buy the correct size you need.

Answer 5

In theory you could do this safely by individually fusing each wire at the source, however I suspect local electrical codes will prohibit this gambit, so I would not suggest it for something connected to the mains.

Answer 6

Using AWG multiple conductor conversion table, 2 conductors of 14 gauge equals 11 gauge which doesn't meet NEC. The other consideration is what happens if one conductor fails if 12 gauge fails there would be a loss of power if one 14 gauge failed the other would take the whole load causing a fire.