I've got a question I'm hoping you all can help me with. I'll try to keep this as brief as possible. Tonight while replacing an outdated outlet, we wound up with some toasty insulation. There are also two switches that were replaced just before the outlet in the circuit. After replacing the outlet and two switches, but before pushing everything back into the receptacles, I flipped the breaker back to test all of the devices. The outlet and lights all functioned properly, so I flipped the breaker again, folded the wires into the receptacles, and tested again. As soon as I flipped the circuit back on I heard the outlet pop. Upon examination it was easy to find where the arc had occurred, due to the blackened spot on the box. I was able to trace this to a nick in the insulation I had missed earlier, which made contact with the box. I was able to snip off the burnt insulation and connect a new outlet, to ensure the previous unit wasn't fried, but it still didn't work. I checked the wires in the receptacle with a voltage detector and found that none of the wires were live any longer. The switches upstream in the circuit work fine, and none downstream work, which makes sense given that the wires in this box seem to be fried. What I can't make sense of is how the circuit seems to interrupted halfway between two receptacles. I am not an expert, but I would have thought a short in the circuit somewhere else would cause the breaker to continually flip and no devices on this circuit would function. The only uneducated guess I have is that the short caused damage to the light switch that is upstream, and caused the circuit to stop there. I haven't yet had time to test this theory by swapping out that switch though, and I would love any input! Thank you all

OK I am adding an attic junction box and 1 new circuit which involves messing around with two 1/2" EMT conduits. I have pulled out the existing #12 solid conductors and plan on using all new stranded conductors which are easier to pull. Between the two 1/2" EMT conduits I need to feed five (6) circuits - all for standard receptacles and lighting purposes. I will be using tandem breakers and sharing the neutral conductors between circuits on opposite legs. So circuits 1, 2, 3, 4, 5, 6 that would be six hot conductors. circuits 1, 2 will have a common neutral, 3 and 4 one neutral, and 5 and 6 one neutral. No need for ground conductors for EMT. Altogether I will have six hot and three neutral conductors between two 1/2" EMT conduits going to the same attic junction box. I think the only way I can do this is to put 3 conductors in one (circuits 1 & 2) and 6 conductors in the other (circuits 3, 4, 5, 6) right? Which lead to the question, is six #12 stranded THHN conductors too much for a 1/2" EMT? The box fill chart says I can put in 9 #12s but that's before derating kicks in. The way I am reading it, if I put four circuits (six conductors) in one 1/2" EMT, and the code says that 4 to 6 current carrying conductors would need to derate by 20%, which means in my case my circuits 3, 4, 5, 6 canNOT be 20A but 15A breakers correct? IF the above is correct, then would it be better for me to divide up the six circuits EQUALLY between the two 1/2" conduits? In other words, put circuits 1, 2, 3 in one conduit (circuit 1 has it's own neutral, circuits 2,3 MWBC), and circuits 4, 5, 6 in the other conduit (circuit 4 has it's own neutral, circuits 5, 6 MWBC). The total number of conductors between the two conduits is actually more (10 total instead of 9) but in each conduit will be 3 hot and 2 neutral. If I do it this way, do I still need to worry abiut derating? Do the neutral conductors count as "current carry conductors"?