[RE-wrenches] Bypass Musings

[drake.chamberlin at redwoodalliance.org]

Hi William,

That looks excellent. I recently purchased a 3rd party interlock for an 
Eaton / Cutler Hammer box, and it does not work securely. Both breakers 
could be switched on at the same time due to the looseness of the fit.

I would like to try one of yours, and be happy to pay you for it.

Thank you,

Drake

_Drake Chamberlin_

_Athens Electric LLC_

_Ohio Electrical Contractor's License 44810_

_NABCEP Certified PV Installation Professional_

---

On 2025-10-14 01:40, William Miller via RE-wrenches 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 [1].  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 [2]
> 
> CA Lic. 773985
> 
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Links:
------
[1] 
https://millersolar.com/MillerSolar/practices/Technical_Procedures/Interlock/Interlock.html
[2] http://www.millersolar.com/
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