PV Negative color [RE-wrenches]

[Allan Sindelar]

  Wrenches,
  John Wiles asked me to forward these notes about conductor color, relevant
to a thread last week:
  Allan at Positive Energy

  ----- Original Message -----
  From: John Wiles
  Sent: Friday, December 07, 2007 1:10 PM
  John Berdner just about said it all.  I'll add the following:
  The color codes in the NEC were developed back when Tom Edison was
generating, guess what, direct current electricity.

  Autos that I have owned and serviced since the early 1960s, mostly
European and Japanese, have largely used white with black stripe for the
negative conductors from all loads to the chassis connection.

  Generators (put-put type) and other sources of power that have the neutral
conductor grounded at the service panel, also have that hot, energized
neutral conductor when there are bad connections in the grounding system.

  Ungrounded PV arrays are allowed (690.35) and are coming.  Red and black
for positive and negative will be the colors of choice for these PV arrays.

  Be cautious in using any color except black for exposed USE-2.  Other
colors do not have as much carbon black, if any, and may not be as sunlight
resistant."
----- Original Message ----- 
From: "John Berdner" <jberdner at sma-america.com>
Sent: Friday, December 07, 2007 11:35 AM
>
> Wrenches:
> Over the years I have spent many hours discussing this issue with John
> Wiles.
> The Code requires grounded neutral conductors to be white.
> The Code makes no distinction between AC or DC on this issue.
> The Code also does not differentiate the white color requirement for
> solidly grounded neutrals or ones with GFDI devices installed.
>
> The red and black automotive "standard" is not applicable or
> appropriate for home sized.
> The last thing I would want is someone to think that a 480 Vdc PV
> system was 12 Vdc was 12 Vdc because of the wrong color wires.
> I also think choice of red and black would be a very difficult decision
> to defend in court since it is a clear violation of the NEC.
>
> Yes, during a ground fault the neutral can become hot at anything up to
> Voc relative to ground.
> This is the exact reason for UL labeling requirement on inverters and
> for my repeated cautions about troubleshooting a system with a ground
> fault.
> Even if both PV positive and PV negative are disconnected, everything
> on the array side of the GFDI device can still be at this potential.
> No matter how close you move the GFDI there will still be some wires
> that could be energized during a ground fault.
> Moving the GFDI closer to the array adds costs in both hardware and
> installation time.


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