Re: wire color marking
- From: phil-news-nospam@xxxxxxxx
- Date: 13 Sep 2008 01:31:36 GMT
On Fri, 12 Sep 2008 23:08:10 GMT Tom Horne <hornetd@xxxxxxxxxxx> wrote:
| phil-news-nospam@xxxxxxxx wrote:
|> On Thu, 11 Sep 2008 05:10:14 GMT Tom Horne <hornetd@xxxxxxxxxxx> wrote:
|> | phil-news-nospam@xxxxxxxx wrote:
|> |> What would be unsafe about the following:
|> |>
|> |> NM or MC cable normally used for a 208Y/120 three phase circuit, consisting of
|> |> a ground wire, and conductors insulated in white, black, red, and blue colors,
|> |> used on a 120/240 volt system, on a split-circuit that traditionally shares a
|> |> neutral, having in this case a split neutral, where the blue wire is marked as
|> |> white using permanent white tape over several inches of the wire at each end.
|> |> One 120 volt outlet is connected to the white wire and black wire. The other
|> |> 120 volt outlet is connected to the blue wire marked white and the red wire
|> |> (the red wire to the hot screw).
|> |>
|> |> Note that NEC 200.6(A) does not permit the above. My question is not about
|> |> what is or is not permitted. It is about what is, or is not, safe, and why.
|> |>
|> |
|> | Long experience has shown that such circuits will be extended, modified
|> | and tampered with by unqualified persons. There is little assurance
|> | that the marking you suggest would be understood or maintained. There
|> | is five conductor cable available with the correct coloration so why not
|> | use that.
|>
|> I have not seen any in type AC.
|>
|
| In areas that allow type NM that type AC arrangement is a special order.
| The demand for that conductor arrangement in type AC cable is
| nonexistent were the less expensive type NM is allowed.
Then I will use three phase AC (green, white, black, red, blue), mark the blue
as white, and challenge the inspector to show me how to avoid using a shared
neutral to a single metal box with AC cable.
Back to my original point: what is unsafe about marking blue as white for
wire sizes smaller than 6 AWG, when it's safe to mark white as red in any
size, and safe to mark blue or black as white in 6 AWG or larger.
Someone could tap into the middle of the cable without regard for how it is
wired at the ends. In the case of single phase cable (green, white, black)
where the white is marked red at the ends, for a 240V circuit, someone not
seeing that red marking in the middle could hook up a 120V branch and end up
with 240V in a 120V outlet.
By contrast, if they tapped in and saw (green, white, black, red, blue), they
might end up connecting a branch circuit to the blue and white, but they would
get 0V instead of the expected 120V. While it would a failed project, at least
it would not kill people.
So I assert that marking and using what appears to be a hot wire as neutral is
safer than marking and using what appears to be a neutral as a hot wire.
So how about this suggested rule change:
For manufactured cable assemblies of type AC, MC, NM, and UF, installed in
dwelling buildings served only by single phase 120/240V electrical service,
where cable assemblies with separate neutrals for two circuits is not
available, a manufactured cable assembly consisting of current carrying
conductors covered by continuous insulation with colors white, black, red,
and blue, may be used to supply two 120 volt circuits with separate neutrals
by marking only the conductor covered with blue insulation using white tape
or equivalent permanent material, and using the wire so marked paired with
the conductor covered with red insulation to make the second circuit.
We want to discourage the use of a shared neutral circuit (or at least I do).
Dual circuit cable is not readily available. I have seen it listed in catalogs
for MC and NM, but it is a special order item. I have not seen it listed at
all for AC and UF.
An alternative for dual circuits is to run TWO cables. But this creates a
real _electrical_ issue when the two circuits supply a common device, or two
or more devices in the same metallic box. That issue is that the grounding
path may not follow the current conductors back to the circuit origin. This
is because the grounding conductors are wired in parallel. In the event of
a fault to metal connected to the grounding wires, the current will split
over both grounding wires. The problem isn't so much that there are two
grounding wires (if both were in the same cable assembly it would not be a
real electrical issue), but the fact that they would be separate.
Other alternatives due exist, but I believe they should not have to be used.
One is to use conduit and wire singles where the two neutrals can be run as
separate colors. Since NEC 200.6(A) limits even this scenario, the only real
option is to use white for one neutral and gray for the other neutral.
Another is to be sure the two circuits feed separate devices in a non-metallic
box.
But I see no hazard issue in using the blue wire as a 2nd neutral when the
building only has single phase power and the blue wire is clearly marked as
to its alternate use.
I do think it should be permitted to mark any color wire of any size as white
or gray to indicate its use as a neutral. But I went ahead and tried to make
the above suggestion as narrow as I could see would be possible.
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