[RE-wrenches] Tranformless inverter

[Bill Brooks]

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:

 

•          “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).

−      (A) Disconnects. All photovoltaic source and output circuit conductors shall have disconnects complying with 690, Part III.

−      (B) Overcurrent Protection. All photovoltaic source and output circuit conductors shall have overcurrent protection complying with 690.9.

−      (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):

•          (1) Detects a ground fault.

•          (2) Indicates that a ground fault has occurred

•          (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.

−      (D) The photovoltaic source and output conductors shall consist of the following:

−      (1) Nonmetallic jacketed multiconductor cables

−      (2) Conductors installed in raceways, or

−      (3) Conductors listed and identified as Photovoltaic (PV) Wire installed as exposed, single conductors.

−      (E) The photovoltaic power system direct-current circuits shall be permitted to be used with ungrounded battery systems complying with 690.71(G).

−      (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.

−      (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 <http://millersolar.com/> 
License No. C-10-773985

 

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