Residential Wiring with nonmetallic sheathed cable (Romex)

[gsassari]

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.

 

[al hildenbrand]

Spend some time with 300.3(B)(3). . .it's easy to stop reading at 300.3(B), but the meat for your questions lays in 300.3(B)(3).

Nothing in installation #2 is wrong by NEC.

Installation #1 would benefit from a hacksaw slot cut through the metal between the two KOs used on the metal j-box of the exhaust fan.

Welcome to the Forum!

Scratch your head over this one and see if you have more questions about it. :smile:

 

[billsnuff]

334.108 egc

334.108 egc

There is also concern about effective ground fault current paths, NEC article 250.4(A)(5), which could be a violation as well.

and 250.4 grounding and bonding.

and what Al said.......

 

[Smart $]

Installation #1 would benefit from a hacksaw slot cut through the metal between the two KOs used on the metal j-box of the exhaust fan.

An alternative is to make entry to the termination enclosure using a romex connector rated for both the mentioned size cables in one connector.

Example of such connectors:
http://aifittings.com/c_1.htm#841
http://aifittings.com/c_19.htm

 

[augie47]

May I add a welcome to the forum.
I am in agreemenrt with Al's answer. In the real world (in this area anyway) the "slot" is seldom cut and I've not seen any real problems, probably due to the realtive low current involved.
Practices vary from location to location, of course, but it is not uncommon here to see a piece of flex used in this sitauation.

Just a side note, changing no answers, but I've not seen a heat-light-fan combination that didn't require a 20 amp circuit. May easily exists, just non-seen in these parts.

 

[al hildenbrand]

An alternative is to make entry to the termination enclosure using a romex connector rated for both the mentioned size cables in one connector.

Indeed.

The instructive thinking about eddy currents comes from what the hacksaw slot does.

 

[Smart $]

May I add a welcome to the forum.

Ditto on that

 

[billsnuff]

Ditto on that

and may I add, Double ditto.......:wink:

 

[220/221]

can one 14/3 and one 14/2 Romex cable be used from the switch box to the appliance

I say no, but two 14/3's is acceptable. The way I understand it is that the neutral must be in the same cable as the hot. I can't say that I havent done it though.

can on 14/3 and one 14/2 Romex cable be used between the two double-gang boxes to provide the five conductors

Same as #1.....in my humble opinion.

 

[infinity]

Just use 4 wire NM cable. Blk, Red, Blu, Wht + grn. IMO you cannot run the neutral in one cable and the switch legs in another. As 220/221 suggested two 14/3's may work if the neutrals in the unit can be separated. You cannot connect the neutrals together on both ends.

 

[al hildenbrand]

Just use 4 wire NM cable.

The OP is giving examples that need a 14/5

 

[TOOL_5150]

The OP is giving examples that need a 14/5

Sometimes I wish that was made and readily avalible.

~Matt

 

[LarryFine]

May I add a welcome to the forum.

Me, too! :smile:


Installation 1:

I've used one 2-conductor and one 3-conductor cable for this, and it's never been an issue. I do color the white in the 2-conductor cable blue, and add a wrap of red or blue tape to the black, and I use the same KO for both cables.

Technically speaking, because there is more than one white pigtail in most multi-function fans, you can use two 3-conductor cables and divide the whites to the two separate neutrals. You should mark the sheath of one cable.


Installation 2:

Because the fan has only a single white, there's no reason to run two 3-conductor cables. You'd either have to parallel the whites (a no-no) or just not use one of them. Clipping one white would give you two pairs of black and red.

But, I would do the same thing as installation 1 above. I'd have a 14-2 (feed) to the first pair of 3-ways, a 14-3 (fan travelers and neutral) and a 14-2 (light travelers) to the second pair of 3-ways, and a single 14-3 to the fan/light.

 

[220/221]

You cannot connect the neutrals together on both ends.

Hmmmm....



2005 300.3 B says:

"...the grounded conductor shall be contained in the same....cable.."

In the fan/light/heat/night light, the grounded conductor is contained in the same cable. There is another grounded conductor in another cable as well but....the grounded conductor is in the same cable. It doesn't say "the only grounded conductor".

 

[LarryFine]

In the fan/light/heat/night light, the grounded conductor is contained in the same cable. There is another grounded conductor in another cable as well but....the grounded conductor is in the same cable. It doesn't say "the only grounded conductor".

That works as long as the load has grounded conductors that can be separated into two groups.

How would you wire two pairs of 3-ways to a two-part load with a single neutral?

 

[220/221]

That works as long as the load has grounded conductors that can be separated into two groups.

Code reference?

I actually opened my book. A RARE occaision.

The ex fan/light will not have separate neutrals but I don't see where it says they have to.

How would you wire two pairs of 3-ways to a two-part load with a single neutral?

The same way as the ex fan. I contend that the code doesn't disallow it.

It says the neutrals must be in the same cable as the hots. They are.

 

[al hildenbrand]

2005 300.3 B says:

"...the grounded conductor shall be contained in the same....cable.."

Look at my red emphasis

2005 NEC 300.3 Conductors

(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).

(3) Nonferrous Wiring Methods Conductors in wiring methods with a nonmetallic or other nonmagnetic sheath, where run in different raceways, auxiliary gutters, cable trays, trenches, cables, or cords, shall comply with the provisions of 300.20(B). Conductors in single-conductor Type MI cable with a nonmagnetic sheath shall comply with the provisions of 332.31. Conductors of single-conductor Type MC cable with a nonmagnetic sheath shall comply with the provisions of 330.31, 330.116, and 300.20(B).

 

[infinity]

The OP is giving examples that need a 14/5

I meant a 14/4 cable which is 14/4 + g = 5 conductors. I did say to use 5 conductors:

Blk, Red, Blu, Wht + grn

 

[infinity]

That works as long as the load has grounded conductors that can be separated into two groups.

I agree, if the unit is internally wired to accept one neutral and three switch legs you need 5 conductors in the same cable.

 

[al hildenbrand]

Code reference?

:smile: 310.4