[RE-wrenches] More Bypass Musings

Wed Oct 15 13:52:33 PDT 2025

For sure, if it is a mission-critical situation where service can't be
provided in a timely fashion, the customer should be able to bypass things.
We do that for clients where we have to take a boat to provide service, for
example.

In the case of an Enphase whole-home battery backup, most around here are
designed for "whole home," but with an adjusted lifestyle. So when the MID
fails, living a normal lifestyle often means depleting the batteries, so it
requires a timely response to avoid a lifestyle change. For example,
shutting down a swimming pool is usually necessary, and possibly water
heating. In some cases, that also means shutting down one of two central
air conditioners.

On the other hand, I had a client whose MID froze open, and they didn't
realize it for almost a month. They ran off-grid on solar and batteries
without a care in the world. Unfortunately, the fix was a real hassle
because the Enphase System Controller contained the service disconnect,
making service difficult and temporary bypass impossible.

For this reason, I have stopped using MIDs (Enphase System Controller or
Tesla Gateway 3) as the service equipment. I don't think that is in the
customer's best interest, especially in states where you have to involve
the utility company and the building department to pull a meter for
service. Adding a 200A service disconnect ahead of the MID is pretty low
cost. It will also make things easier in 15-25 years when the MID
gets replaced with the latest and greatest tech.

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 4:42 PM Dave Tedeyan <dave at sungineersolar.com>
wrote:

> 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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