One 8 AWG wire can handle about 50 Amps. Two would handle 100 Amps.

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Esthy

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I read this in the forum Northern Arizona Wind & Sun: One 8 AWG wire can handle about 50 Amps. Two would handle 100 Amps ... I don't think smaller conductors can be paralleling ... Can be? ... Heat factor? ... Maybe it is for grounding? OR because of my wonderful English I misunderstood?
 
From an electrical standpoint, assuming equal resistance or impedance it would work.

From an NEC standpoint in most cases it is a violation to parallel conductors smaller than 1/0.
 
So, it can be use ... say using two #8 paralleling instead of a single run of #6 for grounding purposes (green)?
 
At least part of the motivation is that in smaller sizes the appropriate larger size is readily available and also reasonable to bend, pull and otherwise work with and is more reliable.

But at some point larger sizes become impractical or unavailable. The NEC has chosen a point at which to draw the line.
Parallel conductors will always require more documentation and more work to insure a safe installation.
 
Esthy said:
I read this in the forum Northern Arizona Wind & Sun: One 8 AWG wire can handle about 50 Amps. Two would handle 100 Amps ... I don't think smaller conductors can be paralleling ... Can be? ... Heat factor? ... Maybe it is for grounding? OR because of my wonderful English I misunderstood?
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The limit is that the conductors to be parallelled have to be #1/0 and larger. And identical in every practical way, so that no one path becomes the preferred "path of least resistance", thus carrying excessive current. My guess is that the size requirement is related to the relative error of manufacturing tolerances. Proportional to total area, the relative uncertainty of a 1/0 wire's area is a lot less than the relative uncertainty of a #8 wire's area.


You can parallel two 50A feeders, if you build them independently as 50A feeders. But you cannot join the conductors at the termination devices on both sides as simply parallel parts of the same feeder. Not until it is 1/0 and larger.
 
Above 1/0 wire size and ampacity are not proportional. Look at the ampacity tables, going from 250 to 500 KCML does not double the ampacity.
So there is no need to parallel below 1/0.
 
It might be a misinterpretation of a single-pole 50 breaker feeding one No. 8, stemming from the belief that a 2-pole breaker feeding two No. 8s can be 100 amps.
 
tom baker said:
Above 1/0 wire size and ampacity are not proportional.
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This is true below 1/0 as well. A change of 3 in AWG is a doubling in cross-sectional area, and a change of 6 is a quadrupling. The ampacity of AWG 2 is much less than 4 times the ampacity of AWG 8, for any insulation temperature rating.

Cheers, Wayne
 
Esthy said:
So, it can be use ... say using two #8 paralleling instead of a single run of #6 for grounding purposes (green)?
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Keep in mind also that for equipment grounds specifically, even when paralleled each ground must be full size based on the upstream OCPD. An example of this would be say a 400A feeder with 2 sets of #3/0 copper, and the ground conductor in each conduit must be a #3. This is intended so that any single ground conductor is sufficiently large to clear a fault within any of the individual raceways.
 
wwhitney said:
This is true below 1/0 as well. A change of 3 in AWG is a doubling in cross-sectional area, and a change of 6 is a quadrupling. The ampacity of AWG 2 is much less than 4 times the ampacity of AWG 8, for any insulation temperature rating.

Cheers, Wayne
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That's true throughout the sizes. If you plot ampacity as a function of kcmil, you will not get a straight line. You will get the same mathematical trend throughout the sizes, so there isn't a sudden change in the physics at any size in particular.
By contrast, if you plot DC resistance as a function of kcmil, you will get a straight line. That is why it is in your advantage to parallel for local feeders, whereas it isn't necessarily as much of an advantage to parallel for long ones when voltage drop plays a controlling role.

Like I said, it is probably the relative uncertainty of manufactured wire tolerances, that prohibit parallel sets below 1/0. Suppose the manufacturing tolerance on all wires is +/- 1 kcmil. There is a big difference in ampacity between a #8 wire that could be anywhere from 15 kcmil to 17 kcmil. Whereas if a #1/0 could be anywhere from 105 kcmil to 107 kcmil, the relative difference in ampacity is a lot less.
 
Carultch said:
Like I said, it is probably the relative uncertainty of manufactured wire tolerances, that prohibit parallel sets below 1/0. Suppose the manufacturing tolerance on all wires is +/- 1 kcmil. There is a big difference in ampacity between a #8 wire that could be anywhere from 15 kcmil to 17 kcmil. Whereas if a #1/0 could be anywhere from 105 kcmil to 107 kcmil, the relative difference in ampacity is a lot less.
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I also have wondered if there is more chance of one conductor having low enough resistance just because of a minor difference in length (even if you tried to get them the same) that it possibly carries more then it's intended share of the load, but with larger conductors you need to have a bigger error in conductor length to have that problem.
 
kwired said:
I also have wondered if there is more chance of one conductor having low enough resistance just because of a minor difference in length (even if you tried to get them the same) that it possibly carries more then it's intended share of the load, but with larger conductors you need to have a bigger error in conductor length to have that problem.
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I've wondered the same thing. Just the difference of one conduit having the inside track around the bends, could mean a couple feet difference. And this is significant enough for a length of 50 ft, to divide a 500A current among parallel 250's such that it loads the shorter set in excess of the 255A ampacity. That is, if you neglect the termination resistances, which helps balance the current.
 
electricalist said:
It was resi. Parallel #10s to a double oven and parallel #8s to a heat unit the condenser.
Branch circuits
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For the double oven from your description I see, two blacks, & two reds both landed on the same breaker. Correct ? Electric furnaces often have one 60A breaker with one 30A breaker. The 60A & 30A would supply two separate heat elements but these are not parallel loads. I think you already know this.
 
I'll have to think it through, it was many years ago. I was working on the roof where the ac unit was not working . As I remember the feeders came through the roof into a j box where 1 phase- 2 conductors. Were sliced by split bolt with 2 more conductors and one conductor went to ac and one to heat unit. The same was done with the other phase. I could be wrong but I remember hearing the heat and the ac aren't on at the same time so it can work.
The oven landed in a 4-11 behind the oven 2 blacks,2 red's. Connected to the oven whip.
 
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