I wanted to borrow some electricity to install a light in a closet. A
3-way switch for the hall light was conveniently located on the opposite side of the same wall. In the box for the 3-way switch I found 4 each two conductor w/ground romex wires. The grounds were all tied together. Three of the insulated wires went to the switch as expected. Three neutrals were tied together, and two hots were tied together. But the two hots that were tied together were not on the same breaker with the light switch. They were on another breaker on the other side of the box, making 240 volts between the switch and the other two hots. So I had two different circuits on different breakers sharing a common neutral that is apparently the only neutral path back to the box. This is all original wiring in a house built in 1976. I know it's all original because the wires were spray painted along with the walls.Is this a common practice I haven't run across before? Does the code allow it?
I realize that since the circuits are on different phases, the common neutral carries only the DIFFERENCE in the loads on the two circuits, not the combined load of both. But it still doesn't feel quite right to me. What if somebody moved one of the circuits to a breaker on the same side of the box. Then the common neutral would carry the combined load and overheat.
DonkeyHody "Every man is my superior in that I can learn from him." - Thomas Carlyle