Do you drop a neutral to the switch box? 300.3(b)

[Finite10]

300.3(b)
(B) Conductors of the Same Circuit. All conductors of the same circuit and, where used, the grounded conductor and all equipment-grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord, unless otherwise permitted in accordance with 300.3(B)(1) through (B)(4)

If there is a dead-end switch box with one single pole switch in it, run in EMT - do you guys run a neutral down to the box along with the current carrying ungrounded?

 

[GoldDigger]

300.3(b)
(B) Conductors of the Same Circuit. All conductors of the same circuit and, where used, the grounded conductor and all equipment-grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord, unless otherwise permitted in accordance with 300.3(B)(1) through (B)(4)

If there is a dead-end switch box with one single pole switch in it, run in EMT - do you guys run a neutral down to the box along with the current carrying ungrounded?

I read that as saying that if they are present they have to be contained in the same raceway rather than split over two raceways, not as requiring them to be present in the first place.

 

[Finite10]

So if I got you right... you read it as;
"... and, where used, the grounded conductor ..."
Meaning, it's not use IN the box, so doesn't need to be run with the ungroudeds.

What about interpreting it as meaning - the 277V circuit uses the grounded conductor- say for lighting?

Also, would 300.20 require the neutral to be run down to the box?

300.20 - Induced Currents in Metal Enclosures or Metal Raceways. (A) Conductors Grouped Together. Where conductors carrying alternating current are installed in metal enclosures or metal raceways, they shall be arranged so as to avoid heating the surrounding metal by induction. To accomplish this, all phase conductors and, where used, the grounded conductor and all equipment grounding conductors shall be grouped together.

 

[mhanson]

As I Understand it, where induction heating is a concern,
the addition of the grounded conductor, weather connected or not, will eliminate the heating.

Also, many motion switches and dimmers require a neutral, which naturally solves this problem.

 

[ActionDave]

If there is a dead-end switch box with one single pole switch in it, run in EMT - do you guys run a neutral down to the box along with the current carrying ungrounded?

Nope, never.

So if I got you right... you read it as;
"... and, where used, the grounded conductor ..."
Meaning, it's not use IN the box, so doesn't need to be run with the ungroudeds.

Yep.

What about interpreting it as meaning - the 277V circuit uses the grounded conductor- say for lighting?

The circuit uses the grounded conductor, but the part of it that goes down to the switch and back does not.

Also, would 300.20 require the neutral to be run down to the box?

300.20 - Induced Currents in Metal Enclosures or Metal Raceways. (A) Conductors Grouped Together. Where conductors carrying alternating current are installed in metal enclosures or metal raceways, they shall be arranged so as to avoid heating the surrounding metal by induction. To accomplish this, all phase conductors and, where used, the grounded conductor and all equipment grounding conductors shall be grouped together.

Nope, the grounded conductor does nothing to avoid inductive heating, the hot and the switch leg do the job just fine all on their own.

 

[GoldDigger]

As I Understand it, where induction heating is a concern,
the addition of the grounded conductor, weather connected or not, will eliminate the heating.

Also, many motion switches and dimmers require a neutral, which naturally solves this problem.

If induction heating is a problem and the neutral is not carrying any current, there will be absolutely no difference in the inductive heating between having it there or not.
Inductive heating happens when an unbalanced current flows through an opening in a ferro-magnetic enclosure or passes through a ferro-magnetic conduit or other raceway.
If you have a balanced wye lighting load which is non-linear, the neutral will carry harmonic current and running it separately from the ungrounded conductors can cause inductive (hysteresis) heating. And since it will be third harmonic and higher, the resulting inductive heating will be at least three times as great as for the same current at the fundamental frequency.

 

[mhanson]

Thank You for the detailed response,

My instructor may have been referring to a single phase system.
stating that the inclusion of the grounded conductor would eliminate inductive heating.

thanks again
Michael Hanson

 

[mike9593]

Dropping Neutral to switch box

Dropping Neutral to switch box

Perhaps not for heating, but 404.3 (c) requires a neutral at every switch. This is to provide the neutral for future electronic dimmers etc.
However, since you mentioned that the raceway is EMT, you can use exception 1, and not provide one...