Residential Wiring with nonmetallic sheathed cable (Romex)

[SAC]

To hold this in my mind, I think about the physics of eddy currents, and the right hand rule (or left hand depending upon one's training. . . at any rate, thumb, fore finger and middle finger extended at right angles to each other). Given the expanding and contracting direction of the magnetic field around any one current carrying conductor that is passing through a hole at a right angle to the plane of some thin ferrous sheet metal, the current induced in the metal will be concentric about the hole.

If another conductor, going through another hole in the same metal, has a matching current of opposite polarity, the induced eddy current will also be concentric, but of opposite direction to the first hole's eddy current.

Now, cut an air gap in the sheet metal, connecting each hole.

The concentric eddy current path is interrupted by the air gap. The two eddy currents of equal and opposite direction cancel each other.

Yes, I agree. But I was intending my question to be more to the point of the OP's "question #1". For example, would running the 14-3 and 14-2 through the same NM cable clamp and through the same KO meet the requirements of 300.20(B)? I wouldn't think so as it wouldn't seem to meet the "insulating wall" part of the clause (whatever that means) - though from an EMF point of view I don't see an issue. It also doesn't seem to allow running one cable through one KO, and the other through a different one - regardless of slots cut - as they are not single conductors as specified in 300.20(B).

 

[al hildenbrand]

For example, would running the 14-3 and 14-2 through the same NM cable clamp and through the same KO meet the requirements of 300.20(B)?

This arrangement satisfies 300.20(A).

It also doesn't seem to allow running one cable through one KO, and the other through a different one - regardless of slots cut - as they are not single conductors as specified in 300.20(B).

That could be worded better. It does seem to read "individual" or "all", but with no mention of "some, but not all".

The language needed for the OP's installation #1 would be made even more difficult because of the four different single pole switches. One has to describe whether "this" conductor, or "that" conductor, or etc., is current carrying.

To side step this, 300.3(B)(3) doesn't say arrange the conductors as single conductors, is says, only, to comply with the "provisions" of 300.20(B) which is the cutting of the slot, or the grouping of the conductors to the area of an insulating panel (a nonferrous panel in the real world). Again, remember, 300.3(B)(3) starts off with the conductors run in different cables.

 

[SAC]

This arrangement satisfies 300.20(A).

But the exemption for multiple NM cables in 300.3(B)(3) requires that it meet the requirements of 300.20(B), and not either 300.20(A) or (B), right? If the conductors for the circuit are all in the same NM cable, then they wouldn't fall into the 300.3(B)(3) exception and then they wouldn't be required to meet the requirements of 300.20(B), and would be covered by 300.20(A). I understand the intent here - I'm just trying to understand what the NEC, as actually written, requires.

 

[al hildenbrand]

But the exemption for multiple NM cables in 300.3(B)(3) requires that it meet the requirements of 300.20(B), and not either 300.20(A) or (B), right?

You are correct. Sorry for the misdirection.

The provisions of 300.20(B) are what one "shall" do, that is (1) and (2), in order to minimize the inductive effect.

If the conductors go through a common single hole, yet are in different cables, the provision of (1) can't be met as there is only one hole, and the provision of (2) doesn't apply as there is no insulating wall present. . .therefore, since neither (1) nor (2) apply, no further provisions need be considered. The single hole with all conductors complies so that the inductive effect is minimized.

 

[SAC]

Thanks Al for laboring through this for me!

-Shawn

 

[nunu161]

being that the heat/fan/light/night light all have thier own neutral in the appliance i dont see a violation in using 2 14/3 cables and just seperate your neutrals accordingly

 

[al hildenbrand]

Thanks Al for laboring through this for me!

:smile:

My pleasure Shawn.

 

[Dennis Alwon]

being that the heat/fan/light/night light all have thier own neutral in the appliance i dont see a violation in using 2 14/3 cables and just seperate your neutrals accordingly

If that is the case then there is no violation however some have stated that not all units are configured that way.

 

[LarryFine]

I'm just trying to understand what the NEC, as actually written, requires.

You're a brave man, Gunga Din!

 

[LarryFine]

No offense was taken. I ask a pithy question and you gave me a pithy response. I appreciate your knowledge.

Just don't get pithed.

 

[LarryFine]

The single hole with all conductors complies so that the inductive effect is minimized.

And, two KO's joined by a cut effectively become a single hole.

That's why you can bring phase-separated conductors (in PVC) into a metallic enclosure if you "connect the dots." A row of KO's joined by cuts behave as a single hole.

 

[quogueelectric]

And, two KO's joined by a cut effectively become a single hole.

That's why you can bring phase-separated conductors (in PVC) into a metallic enclosure if you "connect the dots." A row of KO's joined by cuts behave as a single hole.

What about the steel locknuts??

 

[LarryFine]

What about the steel locknuts??

Um ... er ... uh ... anyone ... help? :roll:

That's a good question ... stop that! D)

Do they make 2" to 4" PVC locknuts?

 

[al hildenbrand]

What about the steel locknuts??

Well, 300.20 is concerned with "enclosures" and "raceways".

A locknut is neither.

I'd say steel locknuts, in the application you are thinking of, is not a NEC issue.

 

[rcelec]

IRC 303.3

I do not see where it says you must have the light and fan on the same switch.
I do not do this unless it is a design issue.And I have never been called on it.

 

[gndrod]

Between the lines

Between the lines

IRC 303.3

I do not see where it says you must have the light and fan on the same switch.
I do not do this unless it is a design issue.And I have never been called on it.

The fan circuit must be locked into the light circuit on an interior bath to satisfy both vent and lighting code requirements. The code violation occurs when the bathroom venting is not used if the light switch is separate. This is a common violation that is not enforced by inspectors not putting mechanical and electrical code requirements together. Very common oversight. rbj

 

[al hildenbrand]

The fan circuit must be locked into the light circuit on an interior bath

The OP fan / heat / light / nite light is a somewhat luxury residential item.

Your "interior bath" is a common commercial location, but not so in residential. I cannot recall ever having seen a fan / heat / light / night light installed in a commercial bath.

It is an uncommon residential bath that doesn't have an operable window. The operable window, in my experience, allows the light switch to only switch the light.

 

[gndrod]

Very common

Very common

The OP fan / heat / light / nite light is a somewhat luxury residential item.

Your "interior bath" is a common commercial location, but not so in residential. I cannot recall ever having seen a fan / heat / light / night light installed in a commercial bath.

It is an uncommon residential bath that doesn't have an operable window. The operable window, in my experience, allows the light switch to only switch the light.

Different strokes for every State. Interior 1/2 baths are very common on the left coast and require full lamp and vent simultaneous operation. This is inspected for all the time. The HO's bring back the EC to disarm or cascade the switching arrangement after the buyoff.

 

[LawnGuyLandSparky]

I have come across two situations in residential wiring when using nonmetallic sheathed cable (romex) that have me concerned if they violate NEC Article 300.3(B) - see bottom of question for NEC article content. I would like a better understanding how Romex cable is used/installed for residential wiring in relation to Article 300.3(B). There is also concern about effective ground fault current paths, NEC article 250.4(A)(5), which could be a violation as well.

Installation #1
A bathroom will have a combination heat/vent/light appliance installed on a 120-volt/15-amp dedicated circuit. A nonmetallic box will be used for the switches and the appliance has a metal enclosure of its own for wiring. The 120-volt line will run from the panel to the switch box then to the appliance. Five conductors are needed from the switch box to the appliance - one common white neutral conductor, and four switch-loops for the heater, fan, 100-watt light, and 7-watt night light. An equipment ground wire will be included. By NEC code, can one 14/3 and one 14/2 Romex cable be used from the switch box to the appliance (no conduit) for the five conductors needed; or must five-single conductors be installed in conduit for the appliance?

Installation #2
A ceiling fan with light will be installed on a 120-volt/15amp lighting circuit. The 120-volt line will run from the panel to a double-gang nonmetallic box containing two 3-way switches, then the wiring will run to another double-gang nonmetallic box containing two more 3-way switches, then the wiring will continue and end at the ceiling fan with light.
The conductors needed between the two double-gang boxes are four travelers and one common white neutral conductor - an equipment ground wire is included. By NEC code can on 14/3 and one 14/2 Romex cable be used between the two double-gang boxes to provide the five conductors needed; or must five-single conductors be installed in conduit between the two double-gang boxes?

Does the National Electric Cable prohibit the use of Romex cables being used in this manner in residential wiring and is there an issue with an effective ground-fault path when two Romex cables, from the same circuit, are used in this manner? SHould a ground-fault occur would the two paths limit the induced ground-fault currents and thus have the potential not to open the overcurrent device?

NEC Article 300.3 (B)
-States all conductors of the same circuit shall be contained within the same raveway, trench, cable, etc. because of electrical theory; that is, the cancelling of currents, to reduce inductive heating, and to avoid increases in overall circuit impedance.
Two other NEC Articles which relate to conductors of the same circuit are NEC Article 300.5(I) and NEC Article 300.2 (A) + (B). Article 300.5 (I) deals with underground installations and 300.20(A)+(B) deals with Induced currents in ferrous Metal Enclosures and Ferrous Metal Raceways. Each of these articles lends support to Article 300.5(B) and give insight and reason.

I am an electrical vocation instructor's aide and have had my Journeyman's Electrician license for less than a year. I care about the quality of educational knowledge I present to the students I instruct. I want my students to care more about installing the most efficient and safest electrical systems that reduce the threat of fires and hazards of electrical shock than to merely build an electricl circuit that works. I am looking for serious responses and it is my hope that someone can help me understand these particular problems more clearly. Thank you for your help.

This poster is the personification of the difference between book smart and street smart. IMHO it should be illegal to be involved in the teaching or professional instruction of ANY subject that the "teacher" has not demonstrated adept, personal professional aptitude in outside of a classroom setting.

It is also MHO the problem with schools and education today, in general, is a result of schools filled with "teachers" whose only claim to fame or success is going through 12 years of public schooling, then 4 years of college, then becomng a "teacher" of history, science, math, etc, instead of having teachers who actually learned their skills and proved their success in the real world, where summers aren't vacations and you work more than 180 days a year...

/rant

 

[realolman]

This poster is the personification of the difference between book smart and street smart. IMHO it should be illegal to be involved in the teaching or professional instruction of ANY subject that the "teacher" has not demonstrated adept, personal professional aptitude in outside of a classroom setting.

It is also MHO the problem with schools and education today, in general, is a result of schools filled with "teachers" whose only claim to fame or success is going through 12 years of public schooling, then 4 years of college, then becomng a "teacher" of history, science, math, etc, instead of having teachers who actually learned their skills and proved their success in the real world, where summers aren't vacations and you work more than 180 days a year...

/rant

All we need to do is find someone who knows everything.:smile:

Even when you take the time to learn everything, they will have changed it on you by the time you have finished. I knew all the answers back in the sixties... I don't know what the heck happened... somewhere along the line they changed the questions.

I think he seems like a very responsible person who posted a very good question, and pretty much knew why it was going to be a good question when he posted it. I can't see gettin yer tail in a knot over that.