Parallel Neutrals

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DBoone

Senior Member
Location
Mississippi
Occupation
General Contractor
Here is the scenerio, 12-2 hot feed comes into Box 1 where there is a 3-way switch for the lights of a ceiling fan/light combo. From Box 1, 12-3 travelers and 12-2 power go over to Box 2. At Box 2 there are 3 switches. A 3-way for the light, a single pole for the fan and a single pole for a flood light. 12-3 is used as the switch leg going to the fan/light and 12-2 goes to the flood light. All neutrals in Boxes 1 are tied together and all neutrals in Box 2 are tied together. Now we have parallel neutrals, the 12-3 traveler neutral and the 12-2 hot feed neutral. I just cannot find any real danger in this setup. It's all the same circuit, all conductors are properly sized for the OCPD. What makes it non compliant? What's the danger?
 

jusme123

Senior Member
Location
NY
Occupation
JW
read 310.4, which states the minimum size for parallel conductors is 1/0 . All you need is one nuetral from box #1 to box #2, because they are the same circuit.
 

DBoone

Senior Member
Location
Mississippi
Occupation
General Contractor
I've seen it stated that the minimum size is 1/0, I just want to know why. I want to know what the real danger is.
 

DBoone

Senior Member
Location
Mississippi
Occupation
General Contractor
Thanks Dave. :thumbsup: I'm still curious about the 1/0 or larger requirement for conductors in parallel. Article 90.1(A) says the purpose of the Code is the safeguarding of persons and property from electrical hazards. What is the hazard of having branch circuit conductors (same circuit) in parallel?
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
There is no danger, and IMO there is no code violation. If only one of the white wires, either in the 12-2 or 12-3, were used a violation of 300.3(B) would be created.

How could there be no violation when you have 2-#12 AWG conductors connected in parallel?
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Do you have another way to run the circuit?

Maybe I didn't read the OP's description enough times, but I see no reason that the neutrals need to be all tied together in box 2. Just separate the neutrals according to the hots. One extra wire nut and no code violation.

I agree there's no danger in this case, however the habit of just always tying all the neutrals together in a box is a bad one. I've seen it done with multiple circuits and that creates actual dangers.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Do you have another way to run the circuit? The scenario described by the OP is quite common and I have done it often using NM and MC.

There other ways to do this and do it without creating a code violation. Just because the violation method may be the easiest way to do it doesn't make it right.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
What is the hazard of having branch circuit conductors (same circuit) in parallel?

There's a bunch of possible concerns. If the conductors aren't the same size and length, but neither by itself has sufficient ampacity for the load, then the smaller one or the shorter one could get overloaded. If the paralleled conductors are not all contained in the same raceway as the return wiring, you can have inductive heating. The concerns are mostly theoretical but the line does have to be drawn somewhere.

Don't ask me to explain the apparently arbitrary restriction on sizes smaller than 1/0. Or why the exception to it applies only to 'control power'.
 

kwired

Electron manager
Location
NE Nebraska
Do you have another way to run the circuit? The scenario described by the OP is quite common and I have done it often using NM and MC.

12-4 with ground or 12-2-2 with ground:happyyes:

I will admit to running two 12-2 with ground cables before in similar situations which is also possibly a violation of 300.3(B). When I have done it I have run both cables together though which does put all the conductors of the circuit in close proximity which IMO is kind of the intent of 300.3(B).
 

kwired

Electron manager
Location
NE Nebraska
As far as what is wrong with paralleling two small conductors, seems like someone posted something more recently that makes some sense as to why this may not be desirable but I can't remember who or what the reason was. Seemed like there was increased possibility of excessive heating in one of the conductors, but then again that would probably be more likely when paralleling for the purpose of increasing ampacity. In OP's situation you still have a 20 amp OCPD and 20 amp individual conductors so there would be no overloading even if one were to carry all of the current.
 
There is no danger, and IMO there is no code violation. If only one of the white wires, either in the 12-2 or 12-3, were used a violation of 300.3(B) would be created.

IMO the original post IS in violation of 300.3(B)

I've seen it stated that the minimum size is 1/0, I just want to know why. I want to know what the real danger is.

As has been stated, there are a number concerns with parallel conductors: particularly equal length and proper connection on each end. A failed connection could result in a conductor carrying twice its ampacity. From 50% of the wire nut connections I see, Its a good idea they have restricted paralleling to 1/0 and larger. I think if you need to parallel 1/0 and larger, you are more likely to know what you are doing and will be using strong, easily inspectable connections/terminations
 

DBoone

Senior Member
Location
Mississippi
Occupation
General Contractor
IMO the original post IS in violation of 300.3(B)



As has been stated, there are a number concerns with parallel conductors: particularly equal length and proper connection on each end. A failed connection could result in a conductor carrying twice its ampacity. From 50% of the wire nut connections I see, Its a good idea they have restricted paralleling to 1/0 and larger. I think if you need to parallel 1/0 and larger, you are more likely to know what you are doing and will be using strong, easily inspectable connections/terminations

How would a failed connection result in a conductor carrying twice it's ampacity?
 

kwired

Electron manager
Location
NE Nebraska
The act of creating incidental parallels Vs paralleling for the purpose of effectively making a higher capacity conductor are two different things. 300.3 does not do a very good job of clarifying just exactly which of these two things (or both) it intends to apply its rules to.

There have also been pretty long threads over some of this content and IMO no real consensus as to whether or not 300.3 only applies to conductors paralleled for the purpose of increased ampacity or if it applies to any conductors installed "in parallel" to one another. Like has been mentioned in the OP's case here neither of the two conductors in question will be overloaded, as the overcurrent protection level is set no higher than the level allowed for only one conductor.

some previous discussions:

http://forums.mikeholt.com/showthread.php?t=149532&highlight=ring+circuit

http://forums.mikeholt.com/showthread.php?t=138335&highlight=ring+circuit


Note my opinions posted in some of those earlier threads may be somewhat different now. I now pretty much feel NEC is not clear enough as to exactly what it intends to apply 300.3 to, but am leaning toward it intending to apply to conductors connected in parallel for the purpose of increased ampacity.
[URL="http://forums.mikeholt.com/showthread.php?t=138335&highlight=ring+circuit"]








[/URL]
 

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
There other ways to do this and do it without creating a code violation. Just because the violation method may be the easiest way to do it doesn't make it right.
I don't think a code violation has been created. I know the code language is not explicit but the reason for rules concerning conductors in parallel only matter if you are trying to gain greater ampacity from a bunch of smaller conductors.

Maybe I didn't read the OP's description enough times, but I see no reason that the neutrals need to be all tied together in box 2. Just separate the neutrals according to the hots. One extra wire nut and no code violation.

I agree there's no danger in this case, however the habit of just always tying all the neutrals together in a box is a bad one. I've seen it done with multiple circuits and that creates actual dangers.
In this case adding a wirenut in the second box would not work because of the fan being on a single pole in the second box but the switch leg up to the fan is a 12-3. Making the three way a dead end in the first box would be a solution.

BTW I agree tying neutral together from multiple circuits can create some real dangers. I'm glad it is one bad habit I never had to unlearn. Most of my bad habits I hang onto because I enjoy them.

How would a failed connection result in a conductor carrying twice it's ampacity?
In your case it wouldn't.

The act of creating incidental parallels Vs paralleling for the purpose of effectively making a higher capacity conductor are two different things. 300.3 does not do a very good job of clarifying just exactly which of these two things (or both) it intends to apply its rules to.

There have also been pretty long threads over some of this content and IMO no real consensus as to whether or not 300.3 only applies to conductors paralleled for the purpose of increased ampacity or if it applies to any conductors installed "in parallel" to one another. Like has been mentioned in the OP's case here neither of the two conductors in question will be overloaded, as the overcurrent protection level is set no higher than the level allowed for only one conductor

......I now pretty much feel NEC is not clear enough as to exactly what it intends to apply 300.3 to, but am leaning toward it intending to apply to conductors connected in parallel for the purpose of increased ampacity
This I agree with.
 

iwire

Moderator
Staff member
Location
Massachusetts
I don't think a code violation has been created. I know the code language is not explicit but the reason for rules concerning conductors in parallel only matter if you are trying to gain greater ampacity from a bunch of smaller conductors.

I am going to have to disagree. If what you said was true there would be no reason for the specific exception allowing it under certain conditions.


Exception No. 1: Conductors in sizes smaller than 1/0
AWG shall be permitted to be run in parallel to supply
control power to indicating instruments, contactors, relays,
solenoids, and similar control devices, or for frequencies of
360 Hz and higher, provided all of the following apply:

(a) They are contained within the same raceway or
cable.

(b) The ampacity of each individual conductor is sufficient
to carry the entire load current shared by the parallel
conductors.

(c) The overcurrent protection is such that the ampacity
of each individual conductor will not be exceeded if one
or more of the parallel conductors become inadvertently
disconnected.
 

iwire

Moderator
Staff member
Location
Massachusetts
There is no danger, and IMO there is no code violation. If only one of the white wires, either in the 12-2 or 12-3, were used a violation of 300.3(B) would be created.

I don't know about the danger but in my opinion it is a violation of the parallel conductor rules.

The 300.3(B) issue can be avoided by using Nonferrous wiring methods as described in 300.3(B)(3)

300.3(B)(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).
 
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