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| Hi, I am in the process of installing a generator transfer switch. I have two sub panels that are seperated by a concrete slab (25 feet apart).
I have three unused 1 1/4 pvc conduits that are underneath the slab connecting both subpanels. (They are within ten feet of both panels). I need to pull (2) 12 amp circuits and (2) 14 amp circuits through with thhn and properly box on both sides and continue with romex to isolate the circuits I need for the transfer switch. (I have 6 x 6 x 4 boxes to successfully pigtail the circuits). I have read the NEC code book and would like to clarify the derating issue. I am staying with dedicated neutrals for each circuit and decided not to run any multi wired circuits. I just want to isolate the circuits for the transfer switch. So I have (8) current carrying conductors in 1 1/4 pipe (I want to keep them in one pipe so I have the other pipes for later use). The NEC states with 90 Degree I should only be worried about derating if the are more than 9 current carrying devices in the pipe. I am correct with this interpretation or do I have to derate with 70 percent for conductors of 7-9. Do the nuetrals count as a current carrying conductor? Should I run 10 guage and 12 guage wire respectively in the conduit to help with derating? Or am I ok? any help is greatly appreciated. |
Follow-Up Postings:
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- Posted by terribletom (My Page) on Sat, Sep 17, 11 at 4:37
| "I need to pull (2) 12 amp circuits and (2) 14 amp circuits through with thhn and properly box on both sides and continue with romex to isolate the circuits I need for the transfer switch." I think you mean two 20-amp circuits (#12 wire) and two 15-amp circuits (#14) wire, so I'm operating on those assumptions. "The NEC states with 90 Degree I should only be worried about derating if the are more than 9 current carrying devices in the pipe. I am correct with this interpretation or do I have to derate with 70 percent for conductors of 7-9. Do the nuetrals count as a current carrying conductor?" You are correct in concluding that derating requirements won't force you to increase conductor sizes until you exceed 9 conductors. What sometimes leads to confusion is that when you begin derating, you start with higher potential ampacities for the wire sizes. In the case of #12 AWG copper, for example, the full ampacity is 30 amps. Although you do, in theory, derate to 70% when there are 7-9 conductors in the raceway, the ampacity allowed still doesn't drop below 20 amps (for #12) or 15 amps (for #14). Therefore, there's no practical effect of the derating when you have up to 9 wires. Yes, with some exceptions, neutrals count as current carrying conductors. (The neutral in a multiwire branch circuit is excepted, since it only carries the imbalance of the two related hots.) Your specs are fine and there's no need to increase wire size to #10/#12 because of derating. |
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| Yeah. After I read it again. I realized I could have been more specific. Sort of bulleted it out without utilizing the proper terms. I appreciate your time and help. Many thanks. |
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