Grounding (was: wire color [RE-wrenches])

[Joel Davidson]

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For years, PV and wind professionals do not ground the DC negative (or DC positive) to avoid lightning damage. Jacobs wind generators floated the DC and grounded the tower and successfully avoided lightning damage. Mobile and marine PV and wind systems operated successfully ungrounded.

Then somebody's so-called good idea forced NEC grounding the DC negative.

Then someone else said that PV arrays could cause house fires so NEC started requiring ground fault protection on residences and the only UL listed DC ground fault protection device was the cludgey board that Trace put together (which I still use on my SW4048 system).

Is there documented evidence of a professionally installed and inspector approved roof-mounted PV array without ground fault protection catching fire? I don't think so.

-----Original Message-----
From: John Berdner <jberdner at sma-america.com>
Sent: Jan 17, 2005 3:04 PM
To: RE-wrenches at topica.com
Subject: Re: Grounding (was: wire color [RE-wrenches])

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Marco / Wrenches:
 
The Code allows DC systems to be ungrounded.
Low voltage systems, high voltage batteries, rectifier derived systems
etc.
Article 690 was where the "that shall ground PV above 50 Vdc (60 Vdc ?
don't remember at the moment)" came from.
 
The why of PV negative grounding is pretty interesting.
After much research I talked to the retired UL engineer who was
involved in getting the language into the Code.
His recollections were vague but essentially it boiled down to "It
seemed like a good idea at the time".
Ward Bower from Sandia remembered that it had to something to do with
the fact the early modules had big problems with the edge seals of the
laminates and ground faults.  The logic was that grounding the array
negative conductor made it easier for the over current devices to work.
Now this was before the days of 1.56* Isc and GFDI's so maybe it made
batter sense then.
 
In the 2005 Code I am pretty sure we get to have ungrounded PV again.
(has anyone seen the real text of the 05 NEC yet ?)
This step forward comes with a bit but....
All wiring in ungrounded PV systems must be double jacketed
multi-conductor or in conduit.
This new requirement is addition to the normal Code requirements for
ungrounded conductors, i.e. over current protection, and means of
disconnect.
On the positive side, ungrounded arrays allow lower cost and higher
performance inverter topologies so in the long run it should be a good
thing.
 
Lastly on color codes: Don' t use Red (pos) and Black (neg).  That is a
pseudo convention for 12 Vdc and should be avoided.
This in addition to the whole Code violation problem.
The grounded Neutral (or PV negative) must be White or Grey (or use
phase tape for big conductors)
The ungrounded conductors should be other colors, e.g. Red, Black,
Blue, etc. 
The equipment grounds should be bare copper, green, or green with
yellow stripe.
 
Best Regards,
 
John Berdner
 
>>>
 
>>> marco at pvthawaii.com 1/17/2005 12:10:29 PM >>>

Ray,
Either I'm missing something here or am really lame. Under what
circumstances are your code-compliant systems ungrounded? I thought
that in
the Land of the NEC ALL PV systems (other than, say, modules on the
roof of
an RV) must have the negative conductor grounded to ground at some
point in
the system.

marco
ProVision

I use red for positive that's legal for all
instances. We use black for neg for lower voltage and when the negative
is
left ungrounded. If it is an ungrounded conductor then it is NOT
required
to be white or grey. It should be black.
If its grounded we use white, or black with white tape stripes. I
think
black wire with a white stripe might be a good compromise. It is
available
in automotive wire.

Ray

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