summoner12
New User
- Location
- Riverside, CA
- Occupation
- Apprentice Electrician
DLDR: Do I calculate my conduit fill from the "A #12 wire is rated for 30 amps @ 90c" or do I start the calculation from #12 is a 20 amp wire according to the 240.4 code?
Long time electrical geek, first time posting (just joined).
My first post and question on this forum is about conduit fill de-rating. I am doing a project at home where I plan to have a panel in my garage and a large junction box centrally located in the home attic. The J-Box will branch out through half the house via Romex. Initially I wanted to run a couple of larger sized conduits to this box and have #12 wire runs.
So I thought "OK, look 1.25" PVC does 43 #12 wires... perfect, way more than I need, I'll run two conduit's and away we go!".
Well, in talking with a person that knows code and is an electrician. He said "well you need to also do your conduit fill de-rating calculations first". He sent me a link about the code 215. something. So I thought "OK, I just need to do the calculation for 90c wire... do the de-rating and I should be good, I'll just need to cut down the number of wires." He reminded me that code 240.4 says that you need to start the calculation from the spec: #12 is 20 amps. He was saying that I can't calculate from the NEC chart that says a #12 wire is 30A, and back track my calculation from that.
I dug a bit on the net and read something that made it sound like the process is: do your calc from the 30a, and if it's lower than the spec in 240.4, you use your calc, but if it's higher than 20A, you must use the 20A rating for that wire. Hence why (in my not professional) experience have always been told "#12 is the wire for a 20 amp circuit and #14 is 15 amp wire". And I just thought "if the conduit holds 43, put 43 wires in there!! YEE HAA!"
Since this is my forever home (I hope) and I plan to do this to spec and overkill. I want to do this right and get answers.
To recap, do I calculate my conduit fill from the "#12 is rated for 30 amps @ 90c" or do I start the calculation from #12 is a 20 amp wire according to 240.4?
Back story on my project. Home was built in 72. The electrical was redone at some point and was severely half assed. Three bedrooms, garage, front entrance lights and large living room with many outlets are all wired to one breaker, all back probed into outlets (no pigtails). I believe it's all on one 20A breaker with #14 Romex. We are getting solar installed soon and our 125A panel will be upgraded to a 200a service. I am having the solar company install a panel I purchased, into my garage as a sub-panel. My panel is a Siemens 200a 60/40. The idea is to slowly rewire the house, splitting up the rooms and upgrading wiring. The main is in a hard to reach area. Going from my sub will make my life a lot easier. I just need to make sure I am doing my calculations right.
Thanks for the help!
Long time electrical geek, first time posting (just joined).
My first post and question on this forum is about conduit fill de-rating. I am doing a project at home where I plan to have a panel in my garage and a large junction box centrally located in the home attic. The J-Box will branch out through half the house via Romex. Initially I wanted to run a couple of larger sized conduits to this box and have #12 wire runs.
So I thought "OK, look 1.25" PVC does 43 #12 wires... perfect, way more than I need, I'll run two conduit's and away we go!".
Well, in talking with a person that knows code and is an electrician. He said "well you need to also do your conduit fill de-rating calculations first". He sent me a link about the code 215. something. So I thought "OK, I just need to do the calculation for 90c wire... do the de-rating and I should be good, I'll just need to cut down the number of wires." He reminded me that code 240.4 says that you need to start the calculation from the spec: #12 is 20 amps. He was saying that I can't calculate from the NEC chart that says a #12 wire is 30A, and back track my calculation from that.
I dug a bit on the net and read something that made it sound like the process is: do your calc from the 30a, and if it's lower than the spec in 240.4, you use your calc, but if it's higher than 20A, you must use the 20A rating for that wire. Hence why (in my not professional) experience have always been told "#12 is the wire for a 20 amp circuit and #14 is 15 amp wire". And I just thought "if the conduit holds 43, put 43 wires in there!! YEE HAA!"
Since this is my forever home (I hope) and I plan to do this to spec and overkill. I want to do this right and get answers.
To recap, do I calculate my conduit fill from the "#12 is rated for 30 amps @ 90c" or do I start the calculation from #12 is a 20 amp wire according to 240.4?
Back story on my project. Home was built in 72. The electrical was redone at some point and was severely half assed. Three bedrooms, garage, front entrance lights and large living room with many outlets are all wired to one breaker, all back probed into outlets (no pigtails). I believe it's all on one 20A breaker with #14 Romex. We are getting solar installed soon and our 125A panel will be upgraded to a 200a service. I am having the solar company install a panel I purchased, into my garage as a sub-panel. My panel is a Siemens 200a 60/40. The idea is to slowly rewire the house, splitting up the rooms and upgrading wiring. The main is in a hard to reach area. Going from my sub will make my life a lot easier. I just need to make sure I am doing my calculations right.
Thanks for the help!
