Neutral required to be run to a disconnect?

[jaggedben]

Suppose I have a remote disconnect for a circuit, that is located such that it makes sense to run the ungrounded conductors to it in one conduit. i.e. line side goes to the disconnect, then load side goes back to through the same pipe to wherever they diverge to go to their respective terminations.

Is there anything in the NEC that says that the neutral has to be present in the same pipe? It will do nothing when it reaches the disconnect except loop out and go right back in.

Thanks in advance for your opinions. :ashamed1:

 

[Smart $]

If under the pervue of the 2011 NEC, 404.2(C) requires a grounded, general-purpose branch circuit to have a grounded conductor run to lighting switch locations. The requirement is excepted if a grounded conductor can be installed if needed at a later date without much ado.

 

[roger]

I agree with Smart but in your case, as far as a disconnect is concerned, the neutral is not required.


Roger

 

[jaggedben]

Thanks for the responses guys. Yes, I did not have a general purpose branch circuit in mind. I'm being asked to run a neutral to a disconnect and I really don't understand why. Fear of certain inspectors, I guess.

 

[Twoskinsoneman]

If the circuit uses an grounded conductor wouldn't it need to be run with the conductors going to the disconnect IAW 300.3(B)?

 

[hurk27]

Thanks for the responses guys. Yes, I did not have a general purpose branch circuit in mind. I'm being asked to run a neutral to a disconnect and I really don't understand why. Fear of certain inspectors, I guess.

He could be trying to use one of the following in error:

250.24(B) which is only for the service disconnect not a feeder or branch circuit disconnect.

300.3(B) ? dead end switches has been allowed for as long as I can remember, 404.2(A) has an exception for 3-ways and 4-ways but in your case not so sure?

300.20(A)? but your installation would cancel this out

 

[jaggedben]

Okay, 300.3(B).

It definitely makes sense to me that this can be read to mean the neutral has to be run 'within the same raceway' out to the disconnect.

If one argues that this is only required of the grounded conductor 'where used', and that the grounded conductor is not 'used' at the disconnect, does this hold any water?

 

[roger]

Okay, 300.3(B).

If one argues that this is only required of the grounded conductor 'where used', and that the grounded conductor is not 'used' at the disconnect, does this hold any water?

That is the the key, if the grounded conductor is not used or neccessary at the disconnect it does not need to be run to the disconnect, the line and load conductors running side by side will negate any stray current, inductive raceway heating, and/or EMF issues.

Roger

 

[stew]

If that neutral is being used anywhere in the circuit that the circuit conductors are running then the neutral has to be run with those conductors.IMHO

 

[Twoskinsoneman]

That is the the key, if the grounded conductor is not used or neccessary at the disconnect it does not need to be run to the disconnect, the line and load conductors running side by side will negate any stray current, inductive raceway heating, and/or EMF issues.

Roger

Is there code allowing this? It obviously makes since regarding the canceling EMFs

 

[hurk27]

I once had to show an inspector how a dead end switch feed cancels out.

all I did was used a clamp on amp probe, and put it around one of the conductors to show there was current, then I put it around both line and load to show him how it now canceled the current out.

anytime you put a clamp on amp meter around all the conductors in a raceway you should always read 0 amps, if not you have current returning another path.

 

[roger]

Is there code allowing this? It obviously makes since regarding the canceling EMFs

It is no different than running two conductors in a conduit to a snap switch, and is even allowed in the exception to the new requirement of 404.2(C).

Roger

 

[Sierrasparky]

should not be required in my opinion in this instance.

 

[jaggedben]

Thanks for all the replies. I have known little about the EMF induction issue so this has been educational.

 

[ronaldrc]

You didn't mention how many circuits.
I agree, with a two wire circuit 120 volt it would should be ok.

If its a 208 volt three wire or 4 wire circuit with more load on one ungrounded
line than the other because the neutral is being used you would need to take it to the disconnect.

I think thats what you all said

 

[jaggedben]

I meant the original question as a general one (it has come up multiple times at my job) but in most cases, and in the latest case that I referred to above, it is a 3-wire 240V circuit, feeding a solar inverter.

I suppose this thread could go on for a while if it gets into how much current is carried on the neutral in a 240V solar inverter output circuit. My impression is very little, but I don't really know what happens if the load becomes unbalanced, or to what extent that is even possible. Probably that should be a new thread.

 

[hurk27]

You didn't mention how many circuits.
I agree, with a two wire circuit 120 volt it would should be ok.

If its a 208 volt three wire or 4 wire circuit with more load on one ungrounded
line than the other because the neutral is being used you would need to take it to the disconnect.I think thats what you all said

Ron, if all the current to a disconnect is returned from the disconnect in the same raceway back to the point it pairs up with the neutral it will still cancel out any field in that raceway, being 3-phase or not has no bearing on it.
I would agree with your above statement if the load left the disconnect in another raceway such as 3-way and 4-way switch loops are done, but in the OP I don't think that is the case?

 

[ronaldrc]

Hi Hurk

I think where on the same page here. I agree if the neutral has no load on it.
But if there is say 30 amps on the neutral and it doesn't go in the same conduit
as the ungrounded conductors to the disconnect and back to the point where it
leaves then the current would not be balanced with the ungrounded conductors.

In order for the conductors to balance out all the current carrying conductors
have to be run together this includes the neutral if it has current on it.

The reason I think this is because a 120/240 volt CT fault sensor has to have the neutral
with it to work or to cancel out all the Mag. flux.
I will admit I'm not sure.

Thats the way I see it anyway.

 

[ronaldrc]

Hurk after third or fourth thought if the conductors are running in the same conduit
to and back in the same conduit, well you are probably right. Just seems like there
should be something wrong there, would the neutral be affected in the J. box ?

 

[hurk27]

Hurk after third or fourth thought if the conductors are running in the same conduit
to and back in the same conduit, well you are probably right. Just seems like there
should be something wrong there, would the neutral be affected in the J. box ?

Yep it's a hard one to grasp and took me playing with a clamp on amp probe to get my head wrapped around it, the neutral does not even come into play here, if all the current that flow into a raceway is returned by the same raceway any current fields are canceled out because current flowing to the disconnect will be 180 deg. out of phase with the current flowing out of the disconnect, even if there is neutral current in the circuit it doesn't matter since the only thing that matters is the current caring conductors in each raceway must mirror each other.

The same in the junction box, all current carrying conductors are in close proximity to each other (unless the box is huge) and will still exhibit the same effect, and since the neutral is in with the fed to the junction box and leaves to the load with all current carrying conductors the same thing happens.

Next time your in a disconnect try clamping a amp probe around both line and load conductors of a circuit, you don't even have to get the neutral in it to prove this, just the line and load, but you will not see any current on that amp probe, at this point they don't have to be in the same conduit since the theory is the same.

Another way to think of this is lets say you have loose open conductors with a load on them that you could bend tight and insert into the coil of an amp meter, do one at a time or all of them since each just runs through the coil and back out through the same coil it cancels out the current field, this would be just like the conductors to the closed disconnect then back into the same raceway.