Hello. Welcome to Just Answer.
Unfortunately, it is against Code to parallel wire that small.
Your distance is not a huge concern, relative to voltage drop, so you don't need to upsize your wire from #8 copper, which is rated for 40 amps.
When can you parallel wire? I am just curious. Thanks!
What are the effects of paralleled wire at smaller gauges?
There is a minimum size that you are allowed to parallel, and it's substantially larger than #12. I don't remember the size offhand, but would be happy to look it up. The only effect would be the Code violation. It would likely work fine. I just wouldn't want to advise you to violate the Code, which would also require removal if you ever try to sell the property.
I understand. It is more of a temp situation in a container I have at my friends warehouse. If you parallel what would 2 12's be? Also, that being the first option, the other one i would like to understand is if I run two 30 amp circuits on 12/3 and
on the use end I combine what would happen (maintaining the phases)
I will in the end use the right wire, 8/3 I just want to understand this as it has been in my head, even if I don;t use it, I like to know how it could work. Might need for a quick and temporary situation one day..
Two 12's paralleled would be capable of handling 40 amps, as each conductor would be rated for 20 amps.
One thing to keep in mind...
If you have a load that will occasionally pull 40 amps, I would feed it with a 60 amp breaker and #6 wire. A sub panel is the ideal solution here, as it would allow you to use a 40 amp 3 pole breaker for the heavy load, and smaller breakers for convenience outlets.
If you parallel two 12-3's, maintaining the colors to keep phasing straight, there wouldn't be any shorts as long as the breakers are positioned properly in the panel. But another Code requirement says no wire smaller than #10 on a 30 amp breaker.
okay well for purposes of the question, if i have two 20 amp 12/3 circuits and I parallel them at the use end, I would get 40 as it would distribute the pull and not trip as the load is ~40?
Yes, that's correct. If the actual load is 40, it could trip the 20's, as you need a little breathing room. We generally don't like to load breakers to more than 80% of their rating, particularly if the load will run for more than 3 hours.
Okay, I think I get it now. I put the ~ on the 40 as I realize that it would have to be under not to trip, I was just making sure the 25 would not trip one of the 20's and that it would equally use the pair. Thanks!