PV Negative color [RE-wrenches]

[John Berdner]

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.
 
Best Regards,
 
John Berdner

>>> Drake.Chamberlin at redwoodalliance.org 12/7/2007 09:24:56 AM >>>

At 08:22 PM 12/6/2007, you wrote:

>I think that a solidly grounded conductor should be
>white, or not, BUT when working with systems using a
>ground fault breaker or fuse and is therefor a fused
>grounded conductor, it should not be white. If a
>ground current makes the wire hot, don't call it
>grounded. If the only way it can become hot is when
>it is broken then it can be called grounded.

This sounds right. The negative wire can exist in junction 
boxes, and if it is white and operating at high voltage DC due to 
the normal operation of the ground fault device, it could pose a 
serious hazard to electricians troubleshooting other systems.

The automotive and marine designations of black and red are 
problematic, due to the fact that black is often positive in NEC 
compliant wiring. Maybe yellow would be a good recommendation for 
negative. The not-always-grounded negative wire on a PV ground fault 
system is a unique, as far as I know.

A far better ground fault system would be one that opened the 
conductors at the array, instead of at the end of the run, where a 
ground fault could continue indefinitely. Control wires could be run 
through the mandated metal conduit to the control center. A hot 
neutral would not be a likelihood.

The 2008 code has new rule to limit the existence of hot, white wires 
by requiring all multi wire branch circuits to open all conductors 
simultaneously. That means that if you are working on a split 240 
volt circuit or a 120/208 Volt 3 phase, all circuit conductors will 
open with a 2 or 3 pole breaker, and it will be safe to disconnect 
the neutral anywhere in the system. As this method becomes mandated, 
the electricians are liable to feel too safe with white wires.

Drake









--
[Non-text portions of this message have been removed]


- - - -
Hosted by Home Power magazine

To send a message: RE-wrenches at topica.com

Archive of previous messages: http://lists.topica.com/lists/RE-wrenches/read

List rules & how to change your email address: www.mrsharkey.com/wrenches/etiquette.php

Check out participant bios: www.mrsharkey.com/wrenches/

Moderator: michael.welch at homepower.com
--^----------------------------------------------------------------
This email was sent to: michael.welch at re-wrenches.org

EASY UNSUBSCRIBE click here: http://topica.com/u/?bz8Qcs.bz9JC9.bWljaGFl
Or send an email to: RE-wrenches-unsubscribe at topica.com

For Topica's complete suite of email marketing solutions visit:
http://www.topica.com/?p=TEXFOOTER
--^----------------------------------------------------------------