Problems with 300.20(A)

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infinity

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I didn't want to hijack this other tread {http://forums.mikeholt.com/showthread.php?t=171589} so I started a new discussion here regarding 300.20(A). In that thread a photo of a lighting contactor was posted and within the contactor there are circuits are being switched to control lighting. The neutrals associated with those circuits are not present in the lighting contactor so the question is does this violate 300.20(A) which states:

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

Also what in the code would specifically allow the use of a two wire switch loop without the neutral being run down to the switch with the ungrounded conductors? For example I have a 200' run of EMT for a SP switch, that raceway would typically have only two conductors, a hot leg and a switch leg.

TCContactor4_zpshs769hcq.jpg
 

jumper

Senior Member
Also what in the code would specifically allow the use of a two wire switch loop without the neutral being run down to the switch with the ungrounded conductors? For example I have a 200' run of EMT for a SP switch, that raceway would typically have only two conductors, a hot leg and a switch leg.

I would say that it is permitted by both 300.20(A) and 300.3(B) for a 2 wire switch loop because both say "where used" and the switch loop does not need a noodle.
 

infinity

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I would say that it is permitted by both 300.20(A) and 300.3(B) for a 2 wire switch loop because both say "where used" and the switch loop does not need a noodle.

I always read "where used" as in any circuit that requires a neutral, like a 120 volt or 277 volt circuit, both of those circuit "use" a neutral. :)
 

jumper

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I always read "where used" as in any circuit that requires a neutral, like a 120 volt or 277 volt circuit, both of those circuit "use" a neutral. :)

But not in the portion of the circuit that is the switch loop.

What good would a noodle do? The inductive heating effect is already cancelled by the switch legs.

Yes, as written, specific permission is not given, but..............IDK.
 

augie47

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I share your questioning and have brought it up in previous discussions.
Since the requirement appears in 300.20, it concerns induced currents. I have litlte knowledge on that subject so I hate to repeat answers I have been given as I can not confirm the basis.
I have been told: (a) since they are "switch legs" with both the supply & return in the same conduit there is no induced current; and (b) the induced current is minimal and thus ignored..
As stated, I can not vouch for the validity of either of those statements and look forward to someone with the knowledge to do so to confirm either
 

infinity

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I share your questioning and have brought it up in previous discussions.
Since the requirement appears in 300.20, it concerns induced currents. I have litlte knowledge on that subject so I hate to repeat answers I have been given as I can not confirm the basis.
I have been told: (a) since they are "switch legs" with both the supply & return in the same conduit there is no induced current; and (b) the induced current is minimal and thus ignored..
As stated, I can not vouch for the validity of either of those statements and look forward to someone with the knowledge to do so to confirm either

I agree with that argument, but still don't see specific wording that allows one to circumvent the requirement of 300.20(A) specifically that if a circuit contains a neutral conductor that it must be run with the circuit conductor. 200.7(A)(1) seems to give some leeway when using a two wire cable to feed a SP switch and re-identifying the white conductor but I don't see a defined exception in 300.20(A) that would allow that either.

I realize that we've been doing this for a hundred years but I'm seeking the actual wording in the NEC that allows this.
 

jumper

Senior Member
I agree with that argument, but still don't see specific wording that allows one to circumvent the requirement of 300.20(A) specifically that if a circuit contains a neutral conductor that it must be run with the circuit conductor. 200.7(A)(1) seems to give some leeway when using a two wire cable to feed a SP switch and re-identifying the white conductor but I don't see a defined exception in 300.20(A) that would allow that either.

I realize that we've been doing this for a hundred years but I'm seeking the actual wording in the NEC that allows this.

This kinda says it. Not a 2 wire SP....

404.2 Switch Connections.
(A) Three-Way and Four-Way Switches. Three-way and
four-way switches shall be wired so that all switching is
done only in the ungrounded circuit conductor. Where in
metal raceways or metal-armored cables, wiring between
switches and outlets shall be in accordance with 300.20(A).

Exception: Switch loops shall not require a grounded
conductor.
 

roger

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But not in the portion of the circuit that is the switch loop.

What good would a noodle do? The inductive heating effect is already cancelled by the switch legs.

That is the answer.

The neutral is not used in this portion of the circuit and would not do anything except waste material.

Roger
 

jumper

Senior Member
Also look at the new section requiring a noodle at a switch box.

We can omit it if it can be installed later, that tells you that it is not required to be installed in the portion of a circuit where it is not used.
 

infinity

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This kinda says it. Not a 2 wire SP....

404.2 Switch Connections.
(A) Three-Way and Four-Way Switches. Three-way and
four-way switches shall be wired so that all switching is
done only in the ungrounded circuit conductor. Where in
metal raceways or metal-armored cables, wiring between
switches and outlets shall be in accordance with 300.20(A).

Exception: Switch loops shall not require a grounded
conductor.

Yes, that specifically addresses 3-way and 4-way switches but not single pole so where is the exception for single pole switches. :)
 

jumper

Senior Member
Yes, that specifically addresses 3-way and 4-way switches but not single pole so where is the exception for single pole switches. :)

There is not a direct one, but if you think about a dead end three way as far as current flow, it is basicly the same as a 2W switch loop.

Power goes to the switch on one wire and returns on another, no noodle needed.
 

infinity

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I'm agreeing that the current flow on a two conductor switch loop would cancel but I'm still not seeing how this gets around 300.20(A). Even the section that Jumper posted (below) about 3-ways and 4-ways specifically sends you to 300.20(A). If you have a 3-way or 4-way there is a specific exception for switch loops but no mention of the same for SP switching.

Where in metal raceways or metal-armored cables, wiring between
switches and outlets shall be in accordance with 300.20(A)
 

Smart $

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I always read "where used" as in any circuit that requires a neutral, like a 120 volt or 277 volt circuit, both of those circuit "use" a neutral. :)
Take another read of 300.20(A)... only this read make your mind conscious of the fact circuit is not used anywhere in subsection (A).

Also keep in mind the purpose: "...[conductors] shall be arranged so as to avoid heating the surrounding ferrous metal by induction.", which is saying all current carrying conductors must have an opposing current conductor grouped with it.

A neutral or grounded conductor running to a switching location is not used if it is not terminated to a load. And if it is not terminated to a load, it is not a current carrying conductor, you may as well not run it (unless required elsewhere by Code).
 

iwire

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Yes, that specifically addresses 3-way and 4-way switches but not single pole so where is the exception for single pole switches. :)

Consider there would have been no need for the relatively new code section specifically requiring a neutral at specific wall switch locations if the neutral was already required by 300.20(A)
 

jaggedben

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If 300.20(A) required the neutral to be brought to a switch, then why did they add 404.2(C) to the 2011 code?

In my opinion language permitting switch loops needs to be added to 300.20(A), because some inspectors don't understand physics. I'm dealing with this right now in one jurisdiction and it infuriates me.
 
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