Timeline for If using an old 240v cable to make two 120v circuits, is there a risk of overheating the shared neutral return?
Current License: CC BY-SA 4.0
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| Nov 11, 2020 at 18:06 | comment | added | NoSparksPlease | 12/3 cable doesn't work with the currently available common configuration of required AFCI circuits, and 12/2/2 NM is typically more than twice the price of 12/2. Your question was only theory, but in practice this modification may produce NEC compliance issues depending on location of the circuits. The NEC requires modifications to a circuit meet current code, you would need to check with your Authority Having Jurisdiction for which addition of the code they last adopted, and local enforcement exceptions, particularly to the AFCI requirements. | |
| Nov 11, 2020 at 17:50 | comment | added | Dan Is Fiddling By Firelight | @brentonstrine in addition to what DoxyLover noted about the breakers, it also requires a 4 wire cable instead of 3; increasing costs in areas where you don't anticipate enough power draw to need more than one circuit. | |
| Nov 11, 2020 at 3:32 | comment | added | DoxyLover | @brentonstrine They do this. As manassehkatz noted, this is called a Multi-Wire Branch Circuit (MWBC). The major disadvantage is that the breakers must trip together so either circuit tripping will also trip the other. | |
| Nov 11, 2020 at 1:44 | comment | added | brentonstrine | That really works out perfectly! Why isn't this strategy used more commonly? E.g. if a room needs two circuits you can run only one cable and have 2 less wires. | |
| Nov 11, 2020 at 0:57 | history | answered | DoxyLover | CC BY-SA 4.0 |