Neutral wire out to a disconnect and back?

[SunFish]

If I run a circuit from a j-box inside to a disconnect outside and then back inside to the same j-box with all the conductors in the same piece of conduit (say 10' long) between the j-box and the disconnect, do you still need to run the Neutral out and back in even though the Neutral doesn't get switched? Or can you just run your line and ground conductors out the disco?

 

[roger]

You do not need to include the neutral in the run, this is basically no different than the conductors running to a single pole light switch except there are a few more.

Roger

 

[GoldDigger]

That is true for a disconnect.

If, OTOH, we replace the outside disconnect with a panel, and put a junction box on the inside from which multiple branch circuits diverge, you would run afoul of the requirement that all of the conductors of one circuit, including the neutrals, originate at the same panel.

 

[Carultch]

If I run a circuit from a j-box inside to a disconnect outside and then back inside to the same j-box with all the conductors in the same piece of conduit (say 10' long) between the j-box and the disconnect, do you still need to run the Neutral out and back in even though the Neutral doesn't get switched? Or can you just run your line and ground conductors out the disco?

I agree with Roger. No need to run a neutral to a disconnect that doesn't do anything with it. Especially in instrumentation-only applications.

The one issue I might have with this, is if your circuit carries imbalanced current. This brings up the issue of 300.3(B), because the imbalance could magnetize the conduit. Maybe 300.3(4) could justify you doing this, but keep it in mind to avoid this when the possibility of significant current imbalances occurs.

I will caution you about running both line and load conductors of the same disconnect in the same conduit. This is OK, as long as both parts of the circuit classify as feeder conductors. If either classifies as service conductors, or tap conductors, you need to keep them separate.

 

[kwired]

I agree with Roger. No need to run a neutral to a disconnect that doesn't do anything with it. Especially in instrumentation-only applications.

The one issue I might have with this, is if your circuit carries imbalanced current. This brings up the issue of 300.3(B), because the imbalance could magnetize the conduit. Maybe 300.3(4) could justify you doing this, but keep it in mind to avoid this when the possibility of significant current imbalances occurs.

I will caution you about running both line and load conductors of the same disconnect in the same conduit. This is OK, as long as both parts of the circuit classify as feeder conductors. If either classifies as service conductors, or tap conductors, you need to keep them separate.

Your 120/240 may be imbalanced, but in your raceway you still have line A out, line A back - both carrying same current and no net magnetic effect on the raceway. Same with line B, or C. Only way you get a magnetic effect on the raceway is if current flows through one conductor in the raceway but does not return through another conductor in that same raceway.

 

[Carultch]

Your 120/240 may be imbalanced, but in your raceway you still have line A out, line A back - both carrying same current and no net magnetic effect on the raceway. Same with line B, or C. Only way you get a magnetic effect on the raceway is if current flows through one conductor in the raceway but does not return through another conductor in that same raceway.

Understood. When there is a round trip path to and from the disconnect, the net current is zero.

What if I route the line and load of the disconnect in separate raceways, and omit the neutral? Suppose I have three identical inverters, each connected phase-to-neutral. And then one of the inverters ceases to produce power. Now we don't have net zero current in the separate line and load raceways.

 

[kwired]

Understood. When there is a round trip path to and from the disconnect, the net current is zero.

What if I route the line and load of the disconnect in separate raceways, and omit the neutral? Suppose I have three identical inverters, each connected phase-to-neutral. And then one of the inverters ceases to produce power. Now we don't have net zero current in the separate line and load raceways.

Then you have a 300.3(B) violation, because all conductors of the circuit and, where used, the grounded conductor are not all in the same raceway or cable.

If running a switch loop whether single pole or multi-pole, supply and return conductors must be in the same wiring method to cancel each other's EMF effects, but a neutral is pointless to run there unless there is a need to switch the neutral also.