Residential Wiring with nonmetallic sheathed cable (Romex)

[SAC]

I would run the hot and neutral to the appliance, and then the switch legs to the switch box.

I know that's not what the OP says, but thats what I would do.

I would agree. I think the answers to the OP's questions are "no" and "no" - neither NM installation as described would be NEC compliant due to having a cable that does not carry both the source and return currents associated with the circuit. I think that a compliant NM solution would be to use a 14-2 to the device to provide un-switched ungrounded and grounded conductors, and then use a 14-2 for each switch loop from the device to the switch (or closest switch, in the case of the 3-ways) and back to the device. In this case each cable carries the full source and return currents for the circuit (zero net current - a clamp on ammeter around any cable always reads zero).

 

[gndrod]

I would agree. I think the answers to the OP's questions are "no" and "no" - neither NM installation as described would be NEC compliant due to having a cable that does not carry both the source and return currents associated with the circuit. I think that a compliant NM solution would be to use a 14-2 to the device to provide un-switched ungrounded and grounded conductors, and then use a 14-2 for each switch loop from the device to the switch (or closest switch, in the case of the 3-ways) and back to the device. In this case each cable carries the full source and return currents for the circuit (zero net current - a clamp on ammeter around any cable always reads zero).

SAC, Why is installation #2 non-compliant in the dead-end example I gave when [404.2(A)]EX allows for loops? rbj

 

[220/221]

That still leaves you needing five conductors to the switchbox. How would you use the colors?

How I would do it and what us compliant is sometimes different


Does the code only allow me to use the white for hot in 3 wire applications?

I have seen and used the a 3 wire cable for two switches the same way I have seen and used a two wire switch loop. Have I sinned again?:grin:

 

[gndrod]

Glass houses

Glass houses

How I would do it and what us compliant is sometimes different


Does the code only allow me to use the white for hot in 3 wire applications?

I have seen and used the a 3 wire cable for two switches the same way I have seen and used a two wire switch loop. Have I sinned again?:grin:

You are not alone.... In the case of the switched dead-end on a 3 conductor B, R, W...the white still gets painted. [200.7(C)(1)&(2)]

 

[LarryFine]

I think that a compliant NM solution would be to use a 14-2 to the device to provide un-switched ungrounded and grounded conductors, and then use a 14-2 for each switch loop from the device to the switch (or closest switch, in the case of the 3-ways) and back to the device.

I want to see you get five 14-2's in one of those fan wiring compartments!

 

[gndrod]

What Larry said.

 

[SAC]

SAC, Why is installation #2 non-compliant in the dead-end example I gave when [404.2(A)]EX allows for loops? rbj

I was referring to the OP - not your example. But my understanding was that the device needed four functions switched (heat/fan/light/night light), and it doesn't look like there are enough insulated conductors in a 14-3 plus a 14-2 to get the job done and still pass the "ammeter test" that I described. Can you be more specific with what conductors in each cable would perform what functions?

 

[SAC]

I want to see you get five 14-2's in one of those fan wiring compartments!

I didn't suggest it was possible to implement - just that it would be correct! I am an the "hated engineer", you know - getting it done is someone else's problem, right? :wink:

 

[rcelec]

The installation instructions for this type of fan call for a 20 amp circuit,a 12/3 to the unit for the heat and night light and their neutrals and another 12/3 for the fan and light and their neutrals.

The second problem...I have no problem.

 

[LarryFine]

I was referring to the OP - not your example. But my understanding was that the device needed four functions switched (heat/fan/light/night light), and it doesn't look like there are enough insulated conductors in a 14-3 plus a 14-2 to get the job done and still pass the "ammeter test" that I described. Can you be more specific with what conductors in each cable would perform what functions?

I don't believe the "ammeter test" is required, since multiple non-metallic cables can be run paralleled and be considered a single, larger multi-conductor cable. A 14-2 and a 14-3 gives you five conductors.

If you really want to perform the ammeter test, clamp it around the entire 2-cable bundle. Obviously, it will read zero net current. If you use a single KO for both cables, no enclosure cut needs to be made.

I would use the white in the 14-3 as the neutral for everything, the black for the fan and the red for the heater. Then I'd use the black (taped) in the 14-2 for the light and the white (re-colored) for the night-light.

 

[LarryFine]

I didn't suggest it was possible to implement - just that it would be correct! I am an the "hated engineer", you know - getting it done is someone else's problem, right? :wink:

Oh, you're not an engineer, you're an architect!

 

[gndrod]

Test & data

Test & data

I was referring to the OP - not your example. But my understanding was that the device needed four functions switched (heat/fan/light/night light), and it doesn't look like there are enough insulated conductors in a 14-3 plus a 14-2 to get the job done and still pass the "ammeter test" that I described. Can you be more specific with what conductors in each cable would perform what functions?

SAC,
My post #33 defined the switched function parameters along with conductor coloring for installation #2. (The dead-end common power feed white is painted black for both traveler sets from the 2gg powered box. The 14-3 switched legs to the ceiling fan from the 2gg power box are Black load 1, Red load 2 and white neutral return.)

For installation #1 the heat/fan appliance load characteristic data is needed to resolve the OP's question along with appliance compartment wire fill concerns. (Refer to 12-2 & 12-3 mentioned by Rcelec.) It would be total speculation to say what cabling is necessary at this time because an interior bathroom would only need one switch leg in both the lighting and vent fan circuit for most AHJ code compliance. (IRC R303.3)

The NM cabling is usually in a residential stick framed installation so I do not see field canceling or induction concerns unless the specs require metal raceways such as an emt project in Chicago. I hope this helps. rbj

 

[Flex]

My apologies Flex. I see you are commercial. A little explaining will help. Residential codes include other trades that impact the NEC in different ways. For instance, the IRC R303.3 requires artificial lighting and venting for bathrooms that do not have at least a 1.5 sf glazing opening for air circulation. In that case, the vent fan and illumination must be controlled on simultaneously. The sf of a bathroom requires 3w/sf [220.12] to determine the lighting sizing basically. (I.e. A bathroom 5' x 8' = 40sf x 3= 120 w lighting.) Does this help? rbj

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

 

[SAC]

I don't believe the "ammeter test" is required, since multiple non-metallic cables can be run paralleled and be considered a single, larger multi-conductor cable.

When I read 300.3(B), it looks to require that all conductors of the same circuit be carried in within the same cable. It then states, "unless otherwise permitted in 300.3(B)(1) through (B)(4)." 300.3(B)(3) is titled "Nonferrous Wiring Methods", and presumably NM cable falls into this clause. That clause then references, for NM wiring, compliance with 300.20(B).

Is that meant to say that all NM wiring methods are exempt from all the conditions listed in 300.3(B), and all that is required is that which is listed in 300.3(B)(3), which for NM wiring means that which is listed in 300.20(B)? That wasn't at all clear to me, as I read it that the reference to 200.20(B) was the only exception to the requirements of 300.3(B), instead of being the only requirement.

Thanks!

 

[SAC]

SAC,
My post #33 defined the switched function parameters along with conductor coloring for installation #2. (The dead-end common power feed white is painted black for both traveler sets from the 2gg powered box. The 14-3 switched legs to the ceiling fan from the 2gg power box are Black load 1, Red load 2 and white neutral return.)

For installation #1 the heat/fan appliance load characteristic data is needed to resolve the OP's question along with appliance compartment wire fill concerns. (Refer to 12-2 & 12-3 mentioned by Rcelec.) It would be total speculation to say what cabling is necessary at this time because an interior bathroom would only need one switch leg in both the lighting and vent fan circuit for most AHJ code compliance. (IRC R303.3)

The NM cabling is usually in a residential stick framed installation so I do not see field canceling or induction concerns unless the specs require metal raceways such as an emt project in Chicago. I hope this helps. rbj

I think the confusion lies in that we are answering different questions. I am answering two very specific questions asked in the OP:

"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?"

and

"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?"

I wasn't trying to read anything more into the question, such as if the given number of conductors are required to meet code, but answering what appeared to be an underlying question about if the conductors for the same circuit could be split among different cables (which I thought wasn't permitted).

 

[al hildenbrand]

Is that meant to say that all NM wiring methods are exempt from all the conditions listed in 300.3(B), and all that is required is that which is listed in 300.3(B)(3), which for NM wiring means that which is listed in 300.20(B)?

Yes.

"unless otherwise permitted in. . . .300.3(B)(3)"

300.3(B)(3) reads "where run in different . . . cables. .". That's the key. 300.3(B)(3) starts out with the premise that the conductors are not grouped in the same cable.

 

[SAC]

Yes.

"unless otherwise permitted in. . . .300.3(B)(3)"

300.3(B)(3) reads "where run in different . . . cables. .". That's the key. 300.3(B)(3) starts out with the premise that the conductors are not grouped in the same cable.

Ok, I see. But does 300.20(B) permit a method for entering a metallic enclosure with multiple conductors of the same circuit which are carried in different cables, unless passed individually, or all together through an "insulating wall"? How do these requirements apply to question #1 in the OP?

With this understanding, I agree this isn't an issue with question #2, as this effectively means that there are no restrictions to running conductors of the same circuit in different NM cables, except where they enter a metallic enclosure.

Thanks for straightening me out on this!

 

[al hildenbrand]

(which I thought wasn't permitted).

:smile:

Interesting, no?

EMF? What, me worry? :roll:

 

[realolman]

I hope gsassari will post what he specifically plans to tell his students.

That was a good practical question... and good responses.

A guy might fool around and learn something hanging around here.:smile:

 

[al hildenbrand]

But does 300.20(B) permit a method for entering a metallic enclosure with multiple conductors of the same circuit which are carried in different cables, unless passed individually, or all together through an "insulating wall"?

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 eddy current about one hole now has to go all the way around the other hole in order to complete its "circuit", and vice versa. The two eddy currents of equal and opposite direction cancel each other.