Um condutor branco é apenas isso, um condutor branco. Só porque é branco não faz automaticamente um neutro. Então, no seu exemplo de loop de comutação, NÃO é um "neutro" que é marcado novamente, é um condutor branco.
Um neutro, ou mais propriamente um "condutor aterrado" menor que o número 4 deve ser branco ou cinza ao longo de seu comprimento. Não pode ser marcado novamente nas extremidades.
Você não pode marcar neutros com outras cores. Se você precisar identificar outra maneira, use números ou rótulos.
2011 NEC
Article 200 Use and Identification of Grounded Conductors
200.6 Means of Identifying Grounded Conductors
(A) Sizes 6 AWG or Smaller.
An insulated grounded conductor of 6 AWG or smaller shall be
identified by one of the following means:
(1) A continuous white outer finish.
(2) A continuous gray outer finish.
(3) Three continuous white stripes along the conductor’s entire
length on other than green insulation.
(4) Wires that have their outer covering finished to show a white
or gray color but have colored tracer threads in the braid identifying
the source of manufacture shall be considered as meeting the
provisions of this section.
(B) Sizes 4 AWG or Larger.
An insulated grounded conductor 4 AWG or larger shall be identified by
one of the following means:
(1) A continuous white outer finish.
(2) A continuous gray outer finish
(3) Three continuous white stripes along its entire length on other
than green insulation.
(4) At the time of installation, by a distinctive white or gray
marking at its terminations. This marking shall encircle the conductor
or insulation.
Para loops de comutadores:
200.7 Use of Insulation of a White or Gray Color or with Three Continuous White Stripes
(C) Circuits of 50 Volts or More.
The use of insulation that is white or gray or that has three
continuous white stripes for other than a grounded conductor for
circuits of 50 volts or more shall be permitted only as in (1) and
(2).
(1) If part of a cable assembly that has the insulation permanently
reidentified to indicate its use as an ungrounded conductor by marking
tape, painting, or other effective means at its termination and at
each location where the conductor is visible and accessible.
Identification shall encircle the insulation and shall be a color
other than white, gray, or green. If used for single-pole, 3-way or
4-way switch loops, the reidentified conductor with white or gray
insulation or three continuous white stripes shall be used only for
the supply to the switch, but not as a return conductor from the
switch to the outlet.
