Transformer-less inverter, was Switching Array leads [RE-wrenches]

[Drake Chamberlin]

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At 07:22 AM 7/30/2007, you wrote:

>The system in the HP article uses a transformerless inverter...so both
>current carrying conductors are ungrounded.

Are there options for having a code compliant, transformer-less 
inverter connected to a wiring system?

These inverters have an incredible advantage over standard models in 
that they can run continuously to power small loads, with extremely 
low current draw.  I keep one on all the time to charge small NiCad 
battery loads.  These units would be perfect for smoke detectors and 
other loads that must stay on.

The disadvantage of the non transformer models, that I'm familiar 
with, are that if you ground the neutral, you destroy the unit.  Are 
there other options now?  What if the case of the inverter were 
double insulated with no case ground?  Would it then be possible to 
ground the neutral?  Has anything become available?

Thanks,

Drake



>David C. Brearley
>Operations Manager
>NABCEP Certified Solar Installer
>
>Meridian Energy Systems, Inc. (TECL: 24461)
>2300 S. Lamar Blvd., Ste. 107
>Austin, Texas 78704
>P: 512-448-0055
>F: 512-448-0045
>david at meridiansolar.com
>www.meridiansolar.com
>
>
>-----Original Message-----
>From: Drake Chamberlin [mailto:Drake.Chamberlin at redwoodalliance.org]
>Sent: Saturday, July 28, 2007 4:02 PM
>To: RE-wrenches at topica.com
>Subject: RE: Switching Array leads[RE-wrenches]
>
>
>The ungrounded conductors must be switched.  In some systems ( I
>think under 50 volts) it is still permissible to not have a grounded
>circuit conductor, but to switch both.   I believe it is code to
>break the grounded conductor with a switch, so long as the ungrounded
>conductor breaks at the same time.
>
>Drake
>
>
>At 06:39 AM 7/28/2007, you wrote:
>
> >As I recall, the older code required both the positive and negative
> >leads of an array to be switched at the array dis-connect. I think
> >at the time there was no DC ground fault required and most of these
> >were low voltage arrays. More recently, I believe the code indicates
> >only the "un-grounded" lead to be switched, which would imply just
> >the positive lead. Since we now have ground fault circuits I think
> >this may also be related to the ground fault working properly since
> >it needs to "see" the potential between the grounding conductor and
> >the negative before it is grounded.
> >
> >However, in the recent issue of HomePower there is a system showing
> >both the positive and negative leads being switched at the array
> >dis-connect. Am I wrong and this is not code, ground fault, or high
> >voltage related issue and it is up to the installer? Since all
> >dis-connects are either 2 or 3 pole, it is not a cost issue, so
> >under what (if any) circumstances would you switch only the positive
> >and allow the negative and array frame grounding conductor to pass
> >through the dis-connect.
> >
> >Thanks,
> >
> >Jeff Yago
>
>
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