Ungrounded Systems (was 600 VDC switches) [RE-wrenches]

[matthew tritt]

Allan,

This should make life interesting. The part about "lower voltage battery
systems" being excluded from this
provision because the components available in the US for those voltages are
designed to be grounded seems, on the face, ludicrous. The components are
designed that way to meet the requirements of the NEC and UL in the first
place! What about the equipment made for a similar purpose in Europe? Do we
get to use it now because it was never intended to be grounded? If Outback,
Trace and others were to produce
components not designed to be grounded, would they then be acceptable to the
NEC?

Another day, another set of rules.

Matt
----- Original Message -----
From: "Allan Sindelar" <allan at positiveenergysolar.com>
To: <RE-wrenches at topica.com>
Cc: "John Wiles" <jwiles at nmsu.edu>
Sent: Friday, October 11, 2002 3:02 PM
Subject: Re: Ungrounded Systems (was 600 VDC switches) [RE-wrenches]


> Wrenches,
> I forwarded John's and Larry's post to John Wiles for his take on this, as
> their points made sense to me, too. John's response is good, so I'm
> forwarding it here.
>
> Allan:
> Post the following at your own risk.  You can tell them its from me if you
> want.  Bill Brooks offered to talk with anyone about the 2005 NEC drafts
in
> a recent post.
>
> The PV community and the code writers have long understood that both
> grounded and ungrounded systems can be installed and operated safely.
There
> are proposals that are being drafted and that will be submitted for the
2005
> NEC that will "permit" ungrounded PV systems.  However to make them as
safe
> as they are and have been in Europe, the balance of systems complexity and
> costs may go up.  Here is the current Draft.  It will be submitted to NFPA
> before 1 November 2002.
>
> 690.35  Ungrounded Photovoltaic Power Systems (New)
>
> Photovoltaic power systems operating at a maximum systems voltage of over
> 125 volts direct current shall be permitted to operate with ungrounded
> circuit conductors where the system complies with (A) through (E).
>
> (A)  All ungrounded photovoltaic source and output circuit conductors
shall
> have disconnects complying with 690 Part III.
>
> (B) All ungrounded photovoltaic source and output circuit conductors shall
> have overcurrent protection complying with 690.9.
>
> (C) All ungrounded photovoltaic source and output circuit conductors shall
> be provided  a ground fault protection device or system complying with
> (1)-(4).
>
>    (1)  Detect a ground fault current at least as low as 1.0 ampere for
each
> 10 kilowatts of PV array (direct current output at Standard Test
> Conditions).
>
> (2)  Interrupt the flow of the detected ground fault current.
>
>    (3)  Indicate that a ground fault has occurred.
>
> (4)  Automatically disconnect the ungrounded faulted conductors and/or
shut
> off the utility-interactive inverter or charge controller for that portion
> of the faulted array.
>
> (D)  The ungrounded photovoltaic source and output conductors shall
consist
> of sheathed (jacketed) multi-conductor cables or shall be installed in
> conduit .
>
> (E)  Ungrounded circuit conductors shall be permitted to be used with
> ungrounded battery systems complying with 690.71(G).
>
> Substantiation
>
> In many parts of the world, photovoltaic power systems are being installed
> and operated safely with none of the PV source circuit or PV output
> circuits.  Peer-reviewed IEEE technical papers have substantiated the fact
> that grounded and ungrounded PV systems may be installed and operated
> safely.
>
> This proposal allows PV system operating at a maximum system voltage of
over
> 125 volts to operate with the PV source and output circuits ungrounded
> providing several conditions are met.  These conditions are similar to the
> conditions under which ungrounded European PV systems are installed and
> operated safely.
>
> The maximum system voltage of 125 volts was selected to preclude the use
of
> ungrounded systems on the lower voltage 24 and 48-volt nominal systems
> because much of the available hardware (switchgear, overcurrent devices,
> ground fault devices, etc) for these lower voltage systems is designed for
> use with grounded systems.  Utility-interactive systems operating at the
> higher voltages will benefit from using ungrounded PV arrays in terms of
> cost and performance.
>
> Paragraphs (A) and (B) require that the ungrounded system complies with
NEC
> provisions found in other articles.
>
> Paragraph (C) ensures that ground faults are detected, interrupted, and
> disable the array or faulted portion of the PV array.  Turning off the
> inverter or charge controller effectively meets the requirement to disable
> the PV array and is allowed.
>
> Paragraph (D) requiring sheathed or jacketed cables or conduit is
consistent
> with European practice requiring double insulation on PV conductors.
There
> are no single-conductor cables in the US that are equivalent to the
European
> double insulated conductors.  For example, European USE-2 single conductor
> cables have an insulation that is nearly twice as thick as the standard
> USE-2 available in the US.  The use of a jacketed cable or conductors
> installed in conduit provides the second layer of insulation and enhances
> the safety of these higher voltage systems where the ungrounded conductors
> are exposed to weathering, ultra violet exposure and possible decay over
> time.
>
> Paragraph (E) allows these higher voltage ungrounded PV systems to be used
> with the higher voltage ungrounded battery systems.
>
> ----- Original Message -----
> From: <jberdner at sma-america.com>
> > The whole grounding paranoia we have here in the US makes no sense to
> > me.  It seems like the regulatory and inspector community has had
> > "ground everything" beaten into them for so long they have forgotten to
> > ask why we do it in the first place. IMHO, the array should be floating,
> > not grounded, at all times and certainly when you work on it.  Solidly
> > grounding the array gives you a single fault lethal hazard which seems
> > stupid to me.  Fortunately the Sunny Boy's ground fault fuse IS the
> > connection to ground and it is allowed to be there by Code because it is
> > part of the GFDI.
>
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