Neutral conductors in 3 way lighting circuits

[Wirenut21880]

I've got a scenario that I have been explaining to people and would like to know the code reference:

-There is a 15A 120V lighting circuit that enters box "A" which is a 2g switch box with (2) 3way switches. There are (2) 14/3 romex going to box "B" which is a 2g switch box with (2) 3 way switches. Leaving box "B" are (2) 14/2 switch legs going to separate lights.

-The correct way to make up your neutrals in box "B" is to connect the neutral from each 14/2 switch leg to the neutral in the 14/3 traveler romex and NOT connect all 4 neutral wires together.

Does anyone know where the code specifies this?

 

[ptonsparky]

Try 310.10(G)

 

[LarryFine]

Does anyone know where the code specifies this?

Not paralleling small conductors should cover that.

 

[electrofelon]

also 300.3(B), all conductors of circuit in same raceway or cable

 

[ptonsparky]

also 300.3(B), all conductors of circuit in same raceway or cable

Even better!

 

[electrofelon]

Also 666.13 - driving the electrician crazy having to tear everything apart to find where the 2 neutrals are tied together that are tripping the AFCI (I know in this case same circuit so wouldn't trip, but in general tying neutrals together that shouldn't be tied=).

 

[ptonsparky]

666.13? New?

 

[wwhitney]

also 300.3(B), all conductors of circuit in same raceway or cable

That's not an issue with NM cable, as 300.3(B)(3) would allow the circuit conductors to be mixed between the two cables; the only concern would be that if the boxes are ferrous, 300.20(B) would require the cables to enter through the same opening.

In fact the circuit arrangement in the OP could be done with (1) 14/3 and (1) 14/2, eliminating the redundant neutral between the two boxes. And if the two NM cables are routed together (say in contact everywhere), I see no downside to such an installation.

Cheers, Wayne

 

[LarryFine]

666.13?

The mark of the devil and a bad-luck number in one article? What could go wrong?

 

[winnie]

666.13? New?

It is an amendment adopted by a higher authority having jurisdiction. Don't do on to future electricians what you wouldn't want them to do on to you.

 

[ptonsparky]

It is an amendment adopted by a higher authority having jurisdiction. Don't do on to future electricians what you wouldn't want them to do on to you.

aahhh....I am slow and old. (Insert Slap forehead emoji)

 

[Fred B]

The correct way to make up your neutrals in box "B" is to connect the neutral from each 14/2 switch leg to the neutral in the 14/3 traveler romex and NOT connect all 4 neutral wires together.

Wasn't an issue connecting all neutrals together until AFCI or when trying to service one circuit and other was energized and the spliced neutral also carried current that would energize to ground in event of someone working on the "supposed" off circuit. Most times wouldn't be noticed until one of these events occurred, as likely this scenario wouldn't normally present with a common tied disconnect of a MWBC, you've unintentionally created a MWBC.
Also a hazard could be created by the unintentional "MWBC" if one neutral to source became disconnected all items would still function, but a possibly overloaded neutral if both circuit's supply were on same phase leg.

 

[ptonsparky]

Wasn't an issue connecting all neutrals together until AFCI or when trying to service one circuit and other was energized and the spliced neutral also carried current that would energize to ground in event of someone working on the "supposed" off circuit. Most times wouldn't be noticed until one of these events occurred, as likely this scenario wouldn't normally present with a common tied disconnect of a MWBC, you've unintentionally created a MWBC.
Also a hazard could be created by the unintentional "MWBC" if one neutral to source became disconnected all items would still function, but a possibly overloaded neutral if both circuit's supply were on same phase leg.

I always considered it an issue, but I was the one assigned to chasing down problems when the ropers screwed up.

 

[OldBroadcastTech]

First, I'm not a licensed electrician, nor do I play one on TV, but...........

WHY is there now a requirement for neutrals to be run along with 'travelers' in 3-way switch circuits ? In my experience, said circuits have worked for numerous decades 'as-was'.

Can someone explain the reasoning behind this requirement ?

Thank you

 

[Fred B]

First, I'm not a licensed electrician, nor do I play one on TV, but...........

WHY is there now a requirement for neutrals to be run along with 'travelers' in 3-way switch circuits ? In my experience, said circuits have worked for numerous decades 'as-was'.

Can someone explain the reasoning behind this requirement ?

Thank you

Many new switching devices some are energy code compliance devices require a neutral connection.

 

[electrofelon]

First, I'm not a licensed electrician, nor do I play one on TV, but...........

WHY is there now a requirement for neutrals to be run along with 'travelers' in 3-way switch circuits ? In my experience, said circuits have worked for numerous decades 'as-was'.

Can someone explain the reasoning behind this requirement ?

Thank you

What fred said. There has been along battle Betwix the NFPA and UL regarding devices using the EGC to power the device. UL never gave in, but the NFPA still added the neutral requirement.

 

[LarryFine]

WHY is there now a requirement for neutrals to be run along with 'travelers' in 3-way switch circuits ?

One reason is to minimize electromagnetic loops.

 

[winnie]

One reason is to minimize electromagnetic loops.

If a switch loop is installed properly, there should be no open loop area in the circuit. Every current in a conductor should be perfectly balanced by current flowing in the opposite direction in an adjacent conductor.

-Jonathan

 

[LarryFine]

If a switch loop is installed properly, there should be no open loop area in the circuit. Every current in a conductor should be perfectly balanced by current flowing in the opposite direction in an adjacent conductor.

Agreed. Sometimes a 3-C cable contains two travelers and a neutral.

 

[wwhitney]

If a switch loop is installed properly, there should be no open loop area in the circuit. Every current in a conductor should be perfectly balanced by current flowing in the opposite direction in an adjacent conductor.

Mostly yes, although 300.3(B)(3)'s allowance for NM cable permits the installation of circuits that result in loops.

But in the recent context of this thread, devices that use the EGC in lieu of a neutral connection may well create current loops, as EGC conductors are all bonded together in any box, rather than being segregated according to their associated ungrounded conductors.

Cheers, Wayne