I've seen on a wire company website that they make a special kind of cable designed to eliminate shared neutral, allowing it to work on GFCI/AFCI protected circuits, or otherwise eliminate those shared neutral issues. The cable is described as having, in addition to the bare ground wire, a black wire, red wire, and two white wires, one of which is striped with red.
But actual catalog pages and price lists I've downloaded don't have this stuff at all. I'm interested in finding out how generally available it is across the country (not just in my own area, which I could find out from an electrical supply place I'm sure). That and which manufacturers make it.
This would just be three-phase cable with the blue wire replaced with a white wire that has a red stripe. Couldn't they have just tweaked the code to allow marking blue as the 2nd white in this special instance? Or would that be too confusing?
I don't follow that price sheet very well. What I want to do is compare the price of cable with (ground, white, black, red, blue) against the price of cable with (ground, white, white/red, black, red) to see if there is a difference in pricing or availability based on the colors. These 2 types of cable are identical except for colors (substitute between blue and white/red), so they should be about the same price unless there is some market issue involved. I'm trying to find out about that.
I called a local electrical supply store the other day. They don't even know what I am talking about. They don't carry Southwire, either. Maybe Southwire is the only source of this?
I've seen romex or a romex-like cable with an extra blue conductor. I presumed it was for a 3-phase circuit or a 3-phase shared neutral triple circuit. But that was years ago. I'll check around again when I get a chance. I'm not expecting it in the discount home supply chain stores.
The price difference Greg Fretwell sees may be explained (somewhat) by economy of scale. A whole lot more 14-2 or 12-2 would be manufactured than 14-2-2 or 14-4, especially in NM. What I want to be sure of is that this is the only explanation by comparing 14-2-2 against 14-4 (and 12-2-2 against 12-4).
Disregarding the NEC violation that would be involved ... if you (as an electrician or inspector) encountered a case where some 14-4 or 12-4 cable (white, black, red, blue) was used, with the blue wire clearly and permanently marked white and also obviously distinct from the original white wire, as a two circuit cable supplying split duplex receptacles, would you considered that to be unsafe in some way?
Since it is electrically no different than using 14-2-2 or 12-2-2 cable, the only safety issues I could imagine would be that this could confuse someone and they rewire things wrong, and do something like putting 240 volts on a 120 volt outlet (by moving the blue-marked-white wire from the neutral bus to a breaker pole opposite of the corresponding red wire). If this is done only in homes (not business or industrial) that only have single phase power (or maybe 2 phases of a 3 phase system), would there still be any significant confusion risk?
How would you wire a split duplex receptacle, with the requirement of not sharing the neutral for compatibility with AFCI, if you only had available 14-2 and 12-2 cable? Would you connect the ground wire in both cables to the one single yoke duplex receptacle (and the box if metallic)? An alternative to the question would involve separate receptacles, but a common metallic box.
If you reidentified a blue wire white I think you bump up against 200.6(A) (A) Sizes 6 AWG or Smaller. An insulated grounded conductor of 6 AWG or smaller shall be identified by a continuous white or gray outer finish or by three continuous white stripes on other than green insulation along its entire length.
If you are going to split the neutral it has to be on the line side of the AFCI unless you can get a 2 pole device made for the purpose. With GFCIs you can split the multiwire circuit and put device type GFCIs on the load side but that is not really practical with AFCIs
I know the rule. What I'd like to know is what the rule is protecting me or someone else from. It's certainly not an electrical thing, given that the difference between blue-marked-white and white-striped-red is insulation color.
What I can see is if there is 3-phase wiring in the building, someone could try tapping the circuit in the middle where they won't see the remarking of the blue, and hook up something like a 3-phase motor. They might be inclined to do that with a 6 AWG or smaller conductor thinking it's an ordinary circuit, whereas seeing something larger they are less inclined to mess with it.
What hazard would exist if the rule were changed to allow remarking blue as white in the narrow circumstances of only 1 or 2 family homes that have only single phase power?