[RE-wrenches] More Bypass Musings

Wed Oct 15 13:42:08 PDT 2025

Jason,

While I agree that it is often fairly simple to bypass an inverter, you
have to be there to do it. I am currently dealing with a Midnite system
that has needed multiple firmware upgrades, and for some reason recently
would not charge the batteries. No one noticed until they completely
discharged, and the backed up loads turned off. We have been able to get
them charging again, but it has been really nice to tell the customer to
just throw the transfer switch and let the loads run off the grid while
this gets sorted out. Tech support has been very helpful, and we've got the
batteries charging again, and I am really glad I did not have to make an
emergency trip to the site to temporarily wire the AC in to the AC out.

AC coupled systems with an MID seem to be a little more resilient in this
fashion though. For that Enphase customer to lose power to the loads, both
the System Controller AND the batteries would have to fail at the same
time. I recently ran into an Avalon SEP that failed. We were able to get it
to still pass through grid power and even get both the AC and DC coupled
solar working immediately. Then at my leisure I was able to go to the site
to troubleshoot (and eventually replace) the SEP. They just did not have
backup power during that time, but at least they had power to the house.

Cheers,
Dave

On Wed, Oct 15, 2025 at 2:50 PM Jason Szumlanski via RE-wrenches <
re-wrenches at lists.re-wrenches.org> wrote:

> I think there’s a real point of diminishing returns here. Even on
> whole-home backup systems, I usually skip a dedicated bypass as long as
> there’s a reasonable way to restore power in a true emergency.
>
> For *off-grid*, it’s definitely convenient to send generator power to the
> loads during inverter service. But if the generator feed is spliced to feed
> both the inverter and one side of a bypass switch, you still have to
> disconnect the inverter feed to make it safe for service, so the benefit
> can be marginal. The real benefit here is for clients to be able to
> self-service to restore power during a component failure.
>
> For *on-grid* systems, I recently dealt with an Enphase System Controller
> failure. There was a separate main disconnect ahead of it (no main breaker
> in the controller), and the load lugs fed the whole house. The controller
> failed with the microgrid interconnect contactor stuck open, forcing the
> client off-grid even though utility power was available.
>
> Bypassing it took nothing more than a pair of 3/0 Polaris taps and about
> ten minutes to splice the line to the load. Would a 200 A bypass switch
> have been worth it? Not really. The quick splice worked fine, and once
> Enphase sent a field tech to replace the MID, I just reversed it – no big
> deal.
>
> Back to off-grid, or on-grid for that matter... This is where a
> well-planned wiring trough shines. You can make quick splices to bypass
> smart loads or even whole-house feeders when needed. On a recent grid-tied
> multi-Midnite AIO installation, I made sure the AC in and AC out power
> distribution blocks were close enough together that I could completely
> bypass the inverters with some quick Polaris tap splices. Or, I could
> quickly remove and cap off a single inverter from the distribution blocks.
> That's even better than a bypass because you can selectively bypass a
> single inverter for service.
>
> Most bypass switches will live their entire lives never being used, so I
> tend to design for practical flexibility rather than theoretical
> perfection. There are definitely situations where a bypass switch is
> mandatory, in my opinion, but when there are options and the risk is low, I
> often save the customer a few bucks after having a conversation with them
> about convenience, cost, reliability/resilience, and serviceability.
>
> Jason Szumlanski
> Principal Solar Designer | Florida Solar Design Group
> NABCEP Certified Solar Professional (PVIP)
> Florida State Certified Solar Contractor CVC56956
> Florida Certified Electrical Contractor EC13013208
>
>
> On Wed, Oct 15, 2025 at 11:26 AM Dave Tedeyan via RE-wrenches <
> re-wrenches at lists.re-wrenches.org> wrote:
>
>> Hi All,
>>
>> Now that some inverters have "smart" load capabilities, I am musing on
>> whether to put in a separate bypass for each smart load. I am thinking
>> specifically about the Midnite AIO inverter, where the Smart loads are
>> powered directly from the inverter, rather than just providing a relay to
>> cut power (like in the Avalon SEP, if anyone has used those). The Midnite
>> AIO also has provisions to run other backed up loads directly from the
>> inverter as well.
>>
>> But if there was a system failure, and you have a bypass switch
>> installed, this will only power the loads in the backed up loads panel from
>> the grid, but not the specific loads that originate from the inverter. Are
>> people installing bypasses for every individual load that originates in the
>> inverter? I was just looking at William's interlock system, but I don't
>> think that you can utilize that kind of system to have some smart loads in
>> there as well. It seems like you can utilize the panel he labels "inverter
>> feed" on his one line diagram to power other backed up loads, but the would
>> not work for a smart load.
>>
>> Cheers,
>> Dave
>> --
>>
>> [image: Logo] <https://www.sungineersolar.com/>
>> Dave Tedeyan, P.E.
>> Owner | Sungineer Solar
>> p: he | him | his
>> a: 1653 Slaterville Rd. | Ithaca, NY 14850
>> w: www.sungineersolar.com <http://www.sungineersolar.com/>
>> c: (607) 270-0370
>> _______________________________________________
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>>
>>
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