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corrected based on comments; edited body
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When a circuit is complete, the neutral line carries current.

If you were to fully load one of the circuits (originally fed by the black wire) with 20 amps, and, at the same time, you were to load the other circuit (originally fed by the red) with 20 amps, you wouldcould have 40 amps returning on the single neutral (at least from the crawlspace junction box back to the panel) under certain circumstances.

While there is a good deal of over-engineering built into the code, I think you areyou could be creating a risk of overloading that neutral line (basically an overheating risk, but perhaps a voltage drop issue as well). I am not sure, but I think under certain circumstances. If you did, the breaker only senses the load on the hot leg, and that overload would not trip the 20+ draw traveling over the neutral.

SUPPLEMENT: [Please see the comments below. Also modified answer above, shown by italics, in light of comments.] As indicated by Tester101 and Matthew PK, if the two breakers are adjacent, they are on different legs of the panel and therefor should not cause an overload on the neutral. If they were on NON-adjacent slots (e.g., if they were on breaker slots 1 and 5), there could be a problem. Breakers can be shifted to different slots (or wires shifted), but only do so if you are well acquanted with electric work, and be certain to turn off the main breaker (often a large pull switch) before handling any individual circuit breakers.

When a circuit is complete, the neutral line carries current.

If you were to fully load one of the circuits (originally fed by the black wire) with 20 amps, and, at the same time, you were to load the other circuit (originally fed by the red) with 20 amps, you would have 40 amps returning on the single neutral (at least from the crawlspace junction box back to the panel).

While there is a good deal of over-engineering built into the code, I think you are creating a risk of overloading that neutral line (basically an overheating risk, but perhaps a voltage drop issue as well). I am not sure, but I think the breaker only senses the load on the hot leg, and that overload would not trip the 20+ draw traveling over the neutral.

When a circuit is complete, the neutral line carries current.

If you were to fully load one of the circuits (originally fed by the black wire) with 20 amps, and, at the same time, you were to load the other circuit (originally fed by the red) with 20 amps, you could have 40 amps returning on the single neutral (at least from the crawlspace junction box back to the panel) under certain circumstances.

While there is a good deal of over-engineering built into the code, you could be creating a risk of overloading that neutral line (basically an overheating risk, but perhaps a voltage drop issue as well) under certain circumstances. If you did, the breaker only senses the load on the hot leg, and that overload would not trip the 20+ draw traveling over the neutral.

SUPPLEMENT: [Please see the comments below. Also modified answer above, shown by italics, in light of comments.] As indicated by Tester101 and Matthew PK, if the two breakers are adjacent, they are on different legs of the panel and therefor should not cause an overload on the neutral. If they were on NON-adjacent slots (e.g., if they were on breaker slots 1 and 5), there could be a problem. Breakers can be shifted to different slots (or wires shifted), but only do so if you are well acquanted with electric work, and be certain to turn off the main breaker (often a large pull switch) before handling any individual circuit breakers.

Source Link
bib
bib
  • 33.9k
  • 10
  • 68
  • 102

When a circuit is complete, the neutral line carries current.

If you were to fully load one of the circuits (originally fed by the black wire) with 20 amps, and, at the same time, you were to load the other circuit (originally fed by the red) with 20 amps, you would have 40 amps returning on the single neutral (at least from the crawlspace junction box back to the panel).

While there is a good deal of over-engineering built into the code, I think you are creating a risk of overloading that neutral line (basically an overheating risk, but perhaps a voltage drop issue as well). I am not sure, but I think the breaker only senses the load on the hot leg, and that overload would not trip the 20+ draw traveling over the neutral.