connecting 10 gauge to 12

[dstrick74]

Hey, how you doing. I have a 30 amp fuse subpanel that is located in my garage. It's for my bedroom that the previous owner added on a few years back I'm assuming. It looks as if there is an outlet for a window ac unit. Hopefully it's 10 gauge 3wire connected to the 30amp 2pole at the main panel in the basement. I don't intend to use the ac outlet. Going to the bedroom, there are (2) 12/2 romexes with ground and (1) thicker romex, I'm assuming that it's for the 2 hots going to the ac outlet. Question is since it's not a long run (about 30 feet) to the bedroom from the main panel, can I just get rit of the old fuse panel, install a junction box in its place, keep the 10/3 from the main panel, disconnect the 30 amp 2pole at the main panel, put one hot on one bus side, the other hot on the other bus, share the neutral and use the 10/3 as seperate 20 amp circuits. Is there a problem connecting a 10 gauge to the 12 gauges that power my bedroom outlets and lights as well as the master bath light. More than likely, I'll disconnect the 3 wire going to the ac outlet and put a cover over the box and label the wire dead. I plan on using the other circuit for my garage outlets. Thanks in advance. I hope it wasn't too confusing.



dstrick74

[suemarkp]

Generally, that would work as long as you use a 20A breaker. You join #10 to #12 with a suitably sized wire nut.

However, there is a fly in the ointment (maybe 2 flies). First, is there a bare grounding wire to the subpanel? A subpanel feeder inside the same structure needs a 4th wire -- the bare ground. Next, bedroom circuits are required to be AFCI protected. You may be able to find a 20A double pole arc fault, but if it is even made for your panel it will be extremely expensive (well over $100). You can't share a neutral with two single pole arc faults.

The 2008 code is most likely going to require arc faults in most places. Therefore, I recommend you leave the panel there and just have two 20A 2-wire branch circuits to your bedrooms. If this panel is old and doesn't take modern AFCI's, replace it with one that does. If it has no ground wire, run a new 10-3 cable or just start over and run everything from your main panel as 12-2 circuits.

Finally, this is the wrong place for this type of question. This section is for how to use the forum not to ask self help questions. It would have been more appropriate in one of the electrical forums.

[dstrick74]

sorry about that. newbie.