[RE-wrenches] Tranformless inverter

Fri Dec 10 21:08:28 PST 2010

Helpful points, thanks Glenn. -August

On Fri, Dec 10, 2010 at 5:23 PM, Glenn Burt <glenn.burt at glbcc.com> wrote:

> I just did a review of the TL inverters by SMA for possible use.
>
> A few points that are relevant:
> They require the use of an external fused combiner (they also sell). It has
> support for up to 6 strings, with both + and – fuse positions provided.
>
> The integrated DC disconnect has no fusing – it will accept only two
> conductors
>
> The manual says these inverters are supposed to be installed in threes
>
> They only work on 208VAC
>
> Obviously they are lighter than their transformer based cousins
>
> There is a warning to beware of stray array capacitances in excess of 2
> micro Farads or more and 50mA from the cells to ground or the inverter will
> disconnect
>
> Obviously an EGC is still necessary from the frame of the array
>
> Required clearance around the inverter has been increased to 12” (36”
> below)
>
> Replaceable varistors are used to protect DC inputs from high voltages
> (inside DC disconnect)
>
> Still 600VDC upper limit
>
> AC max conductor diameter is 2AWG, min is #6
>
> DC conductors - #10 to #6
>
> They recommend operating the DC disconnect once a year, 10 times to keep
> the contacts clean
>
>
>
> FYI – thought I’d share.
>
>
>
> -Glenn Burt
>
>
>
>
>
> *From:* re-wrenches-bounces at lists.re-wrenches.org [mailto:
> re-wrenches-bounces at lists.re-wrenches.org] *On Behalf Of *August Goers
> *Sent:* Friday, December 10, 2010 3:50 PM
>
> *To:* RE-wrenches
> *Subject:* Re: [RE-wrenches] Tranformless inverter
>
>
>
> Hi Bill and Wrenches -
>
>
>
> For ungrounded arrays what specific fusing and or DC disconnect
> requirements are needed compared to grounded arrays?
>
>
>
> I'm trying to sort through the code but nothing is popping out at me
> besides what was already mentioned about needing to disconnect both the
> positive and negative lines on the DC side. In SMA's case I'm guessing that
> their new transformerless inverters with integrated DC disconnects and fuses
> may already take of all the requirements?
>
>
>
> Best,
>
>
>
> August
>
>
>
>
>
> August Goers
>
>
>
> Luminalt Energy Corporation
>
> 1320 Potrero Avenue
>
> San Francisco, CA 94110
>
> m: 415.559.1525
>
> o: 415.641.4000
>
> august at luminalt.com
>
>
>
>
>
>
>
> *From:* re-wrenches-bounces at lists.re-wrenches.org [mailto:
> re-wrenches-bounces at lists.re-wrenches.org] *On Behalf Of *Bill Brooks
> *Sent:* Friday, October 01, 2010 8:29 AM
> *To:* 'RE-wrenches'
> *Subject:* Re: [RE-wrenches] Tranformless inverter
>
>
>
> All,
>
>
>
> Transformerless inverters are simply a subset of ungrounded or resistively
> grounded PV systems covered by the NEC in 690.35 since the 2005 code cycle.
> Power-One has been marketing their ungrounded inverter in the U.S. for
> several years now. It was listed by CSA. The requirements for ungrounded
> systems in 690.35 are as follows:
>
>
>
> &bull              “Photovoltaic power systems shall be permitted to
> operate with ungrounded photovoltaic source and output circuits where the
> system complies with 690.35(A) through 690.35(G).
>
> &minus      *(A) Disconnects. *All photovoltaic source and output circuit
> conductors shall have disconnects complying with 690, Part III.
>
> &minus      *(B) Overcurrent Protection. *All photovoltaic source and
> output circuit conductors shall have overcurrent protection complying with
> 690.9.
>
> &minus      *(C) Ground-Fault Protection. *All photovoltaic source and
> output circuits shall be provided with a ground-fault protection device or
> system that complies with (1) through (3):
>
> &bull              (1) Detects a ground fault.
>
> &bull              (2) Indicates that a ground fault has occurred
>
> &bull              (3) Automatically disconnects all conductors or causes
> the inverter or charge controller connected to the faulted circuit to
> automatically cease supplying power to output circuits.
>
> &minus      *(D) *The photovoltaic source and output conductors shall
> consist of the following:
>
> &minus      (1) Nonmetallic jacketed multiconductor cables
>
> &minus      (2) Conductors installed in raceways, or
>
> &minus      (3) Conductors listed and identified as Photovoltaic (PV) Wire
> installed as exposed, single conductors.
>
> &minus      *(E) *The photovoltaic power system direct-current circuits
> shall be permitted to be used with ungrounded battery systems complying with
> 690.71(G).
>
> &minus      *(F) *The photovoltaic power source shall be labeled with the
> following warning at each junction box, combiner box, disconnect, and device
> where the ungrounded circuits may be exposed during service:
>
> WARNING
>
> ELECTRIC SHOCK HAZARD
>
> THE DC CIRCUIT CONDUCTORS OF THIS
>
> PHOTOVOLTAIC POWER SYSTEM ARE
>
> UNGROUNDED AND MAY BE ENERGIZED
>
> WITH RESPECT TO GROUND DUE TO
>
> LEAKAGE PATHS AND/OR GROUND FAULTS.
>
> &minus      *(G) *The inverters or charge controllers used in systems with
> ungrounded photovoltaic source and output circuits shall be listed for the
> purpose.
>
>
>
> We now have several products newly on the market to include on the list
> such as the SMA and Exeltech products. Ungrounding the array requires
> additional fusing and disconnects, but the most significant difference is
> that the module wiring and all external cable must be PV Wire/Cable.
> Therefore only modules with PV Wire/Cable can be used in these systems. You
> must confirm from the manufacturer that they have made the switch. Hopefully
> all manufacturers will be installing PV Wire/Cable soon so that this will
> not be a problem anymore.
>
>
>
> It is a good call to use up your USE-2 and order PV Wire/Cable from now on.
>
>
>
> Bill.
>
>
>
> *From:* re-wrenches-bounces at lists.re-wrenches.org [mailto:
> re-wrenches-bounces at lists.re-wrenches.org] *On Behalf Of *Exeltech
> *Sent:* Friday, October 01, 2010 6:39 AM
> *To:* RE-wrenches
> *Subject:* Re: [RE-wrenches] Tranformless inverter
>
>
>
> Transformerless grid-tie inverters are permitted under the National
> Electric Code as of 2008.  The Nationally Recognized Testing Laboratories
> (UL, ETL/Intertek, CSA, etc.) took a while to develop the testing procedures
> for testing to UL1741, which was the basis for most of the delay.
>
> SMA isn't the only company with transformerless grid-tie inverters.  I know
> of one American manufacturer with transformerless models on the market as
> well.
>
> Transformerless inverters are smaller, much lighter, and tend to be more
> efficient than transformer-based units.  No transformer also means lower
> product cost, and less shipping expense.  Win-win-win.
>
>
> Dan
>
>
> --- On *Fri, 10/1/10, Drake <drake.chamberlin at redwoodalliance.org>* wrote:
>
>
> From: Drake <drake.chamberlin at redwoodalliance.org>
> Subject: Re: [RE-wrenches] Tranformless inverter
> To: "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
> Date: Friday, October 1, 2010, 6:58 AM
>
> I also received this advertisement.  Previously I had investigated the
> smaller SMA transformerless inverters, and was told that this type would not
> be allowed in the US until the 2011 code.  Has the ban been lifted?
>
>
>
> At 12:52 AM 9/29/2010, you wrote:
>
> Wrenches:
>
> I received an advertisement from a distributor that SMA is now shipping 8,
> 9 and 10 KW transformerless inverters.  Don't these require double insulated
> PV wiring and no connection  to ground on the AC side? It's been too long
> since this subject last crossed my desk and I want to refresh my memory on
> the specifics.
>
> William Miller
>
>
> *Please note new e-mail address and domain:
>
> *William Miller
> Miller Solar
> Voice :805-438-5600
> email: william at millersolar.com
> http://millersolar.com
> License No. C-10-773985
>
>
>
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-- 
August Goers

Luminalt Energy Corporation
1320 Potrero Avenue
San Francisco, CA 94110
O: 415.641.4000
M: 415.559.1525
august at luminalt.com
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