[RE-wrenches] Bypass Musings

[Dave Tedeyan]

Hi William,

Thanks for sharing. I like your interlocking system, especially for when
you need to run a load panel that is >100A. Have you ever had an inspector
give you a hard time about making your own interlock, rather than using
something listed?

For 100A load panels or less, I have found something like the GE TC10323R
to be well enough priced. Most hybrid inverters have load breakers, so I'll
just bug those together in the gutter if there is more than one inverter.
However, as you mentioned, the 200A versions of these double throw transfer
switches are quite pricey.

Cheers,
Dave

On Tue, Oct 14, 2025 at 1:55 AM William Miller via RE-wrenches <
re-wrenches at lists.re-wrenches.org> wrote:

> Friends:
>
>
>
> For many years I had committed to the Outback product line.  The decline
> of Outback forced me to branch out.
>
>
>
> I just completed my first install of Fortress Envy inverters.  Not long
> ago I installed a Sol-Ark 12K in my shop.  Both experiences were mostly
> positive.
>
>
>
> What is interesting is the Envy and Soul-ark inverters do not come with
> BOS equipment.
>
>
>
> Now, if you want a PV disconnect, you need to add one manufactured by a
> third party.  This can be accomplished with a 600 volt safety switch.
>
>
>
> If you want AC disconnecting means or distribution, you need to provide
> outboard equipment.  This is easily provided with off-the-shelf circuit
> breaker panels.
>
>
>
> Since my second Radian install I have avoided putting AC breakers in the
> GSLC because wiring them was beyond tedious.  Instead I ran my AC leads
> right through the GSLC and straight to one of two breaker panels:  A
> generator-fed panel and in inverter-fed panel.  Therefore I am not
> inconvenienced by lack of AC BOS with the new generation inverters.
>
>
>
> There is one other function that is missing with the lack of BOS
> cabinets:  Bypass switching.  I think it is imperative that bypass
> capabilities be provided.  Inverters can fail and occasionally need service
> and a bypass makes these scenarios much easier to handle.  As a matter of
> policy I will not support a batter-inverter client if they do not have a
> bypass.
>
>
>
> The Fortress and Sol-Ark manuals recommend use of an outboard double throw
> switch for bypass.  These are expensive and bulky.
>
>
>
> Over the years I have developed circuit breaker interlocks that can be
> fitted in a standard breaker panel and take care of the bypassing function
> cheaply and efficiently.
>
>
>
> For a long time I have been meaning to write an article on the subject of
> transfer switches and bypass options.  I finally got around to it and it
> can be found here
> <https://millersolar.com/MillerSolar/practices/Technical_Procedures/Interlock/Interlock.html>.
> I hope my efforts writing this might provide some insight on the subject.
>
>
>
> I think I have fine-tuned my interlock design to a final iteration, as
> described in the article.  If any of you are interested in trying out my
> Universal Bypass Interlock I am willing to send one for you to try at no
> cost.  Contact me off list if you are interested.
>
>
>
> Sincerely,
>
>
>
> William Miller
>
>
>
> Miller Solar
>
> 17395 Oak Road, Atascadero, CA 93422
>
> 805-438-5600
>
> www.millersolar.com
>
> CA Lic. 773985
>
>
>
>
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