[RE-wrenches] Recommendation on DC Breaker/Musings on PV disconnecting/Tigo warning

Thu Jan 18 12:01:35 PST 2024

Thank you William,
   I stock those breakers in large numbers and purchase them from the
manufacturer. We're it not that I leave in 10 hours for the rest of the
winter I would have just sent a bunch to Jay, but time is of the essence.
That is the only reason for the (poor) recommendation.

Best,
Daryl

On Thu, Jan 18, 2024, 2:57 PM William Miller via RE-wrenches <
re-wrenches at lists.re-wrenches.org> wrote:

> Friends:
>
>
>
> I am not familiar with the inverter cited and I am not going to take the
> time to research it.  There are too many options this day to keep up!
>
>
>
> If this system requires load disconnecting, a touch safe fuse holder is
> not the correct device.  They are not rated for load break.  A work-around
> is to plainly indicate the inverter AC disconnect should be activated or
> the inverter turned off before opening the fuse disconnect.
>
>
>
> Also, please consider not shopping at Amazon.  They have a terrible record
> regarding employee safety.  PV-Cables carries this fuse holder at a
> competitive price and they are great people to work with. Here is a link:
> https://pv-cables.com/product/littelfuse-spf-solarfuse-holder/.  There
> are many other solar vendors that have these and that could use your
> shopping dollars.
>
>
>
> Below are some related subjects I have been pondering:
>
>
>
> RSS as PV disconnecting means:
>
>
>
> I have been whining at great length about having to install RSS MLPE on
> off-grid installations.  My most pathetic whining has been about having to
> install these on ground-mount arrays.  My understanding is that RSS is
> supposed to protect fire fighters when they respond to structure fires.
> How does an RSS system on a ground mount even apply here?
>
>
>
> However, I do find it handy to have an easy way to de-energize PV circuits
> so I can safely work in combiners and recombiners.  This makes me wonder:
> Is module level RSS equipment suitable to act as PV disconnecting means?
>
>
>
> Tigo Transmitter-Where should it be installed? And a warning:
>
>
>
> I like to be able to measure PV circuits when connected and disconnected.
> If the Tigo RSS transmitter donut is installed down-stream of the PV
> disconnecting means then open circuit measurements are not possible.  If
> you open the disconnect, the keep-alive signal goes away and you can’t
> measure the PV string.
>
>
>
> I got a surprise when doing just this a few days ago.  I have two rows of
> PV racks and a combiner on each row.  If I want injection of Tigo
> keep-alive signal upstream of the combiner breakers, I need to install a
> transmitter in both combiners.  I looped the feeders to the far combiner
> through the near combiner. The Tigo donut in the near combiner was near
> those looped feeders and induced enough signal in the feeders that the RSS
> MLPE in the next rack were switched on.  I got a nasty 200 VDC shock out of
> the deal.   See photo below.
>
>
>
>
>
> Automatic RSS:
>
>
>
> As noted above, everything I have read about RSS is that it is designed
> for the safety of fire fighters.   RSS is a manually activated system.
> Someone needs to find and push or twist the disconnect button.  If this is
> not done the RSS provides no protection.  Why could we not require AFCI and
> GFDI equipped inverters and charge controllers to provide a contact closure
> in case of either fault that could easily be wired into the RSS system to
> activate the RSS automatically?  Seems like a no-brainer to me.
>
>
>
> True PV safety for fire fighters and the public:
>
>
>
> I was watching a webinar
> <https://www.youtube.com/watch?v=MyBe21Q3xCQ&t=629s&ab_channel=MayfieldRenewables>
> on UL 3741 recently.  In it the presenter early on makes the claim that PV
> systems are “inherently safe” (8:45 in the video).  I think this is wrong.
> String PV systems are inherently *unsafe*, for two reasons:  1. PV panels
> have no off switch.  If the sun is shining the panels are creating power,
> at potentially fatal levels.  2. PV panels cannot trip OCPD.  PV panels are
> finite in ampacity and we need the OCPD to be rated at above the available
> current.  In case of a fault an AFCI or GFDI equipped inverter or charge
> controller can detect those faults and shut off, but the fault still exists
> and is still being fed power.  These concerns apply to PV string systems.
> Micro-inverter systems could be argued as being inherently safe.
>
>
>
> To get to true PV safety, we need to find a way to shut off power at the
> source.  If we can trigger MLPE RSS to shut off in the case of detectable
> faults, we are much closer to the holy grail of true safety.
>
>
>
> The interconnection of AFCI and GFDI inverters and charge controllers with
> RSS is one way to achieve this goal.  This should be easy to achieve-- it
> requires only a contact closure be built into the electronics.  Outback’s
> FM100 charge controllers have a contact closure that can be programmed to
> open in the case of an error, but not the errors we need.  So close…
>
>
>
> Thinking this through further, why not build AFCI and GFDI protection
> right into MLPE electronics?  That way in the case of a fault the power is
> shut off at the source.  Maybe Solar Edge does this already.  Does anyone
> know?
>
>
>
> UL3741:
>
>
>
> I have just started studying UL 3741.  From what I have learned so far, I
> am not convinced this is the right direction.  For one, the standard
> upgrades the allowed voltage exposure to 160 VDC.  Number two, the standard
> is written only to protect fire fighters.   This leaves out protecting the
> public.  This includes kids climbing on a ground mount or using a piece of
> copper pipe to retrieve a Frisbee from under a PV array, or a homeowner
> falling into a PV array while hanging holiday decorations on a dormer-- to
> name just a few scenarios.  Number three, the goal is to eliminate MLPE.
> Until PV panels come with an accessible off switch, we need MLPE.  We
> cannot have power sources so ubiquitous to our lives that can’t be turned
> off.
>
>
>
> As an industry, I think we have not prioritized PV safety nearly as much
> as the industry does for regular electric equipment safety. If you don’t
> believe me, try running conductors to a roof-top air conditioning unit
> without conduit protection and see what your inspector thinks about that.
>
>
>
> I am interested in thoughts any of you may have on the above topics.
>
>
>
> William
>
>
>
> Miller Solar
>
> 17395 Oak Road, Atascadero, CA 93422
>
> 805-438-5600
>
> www.millersolar.com
>
> CA Lic. 773985
>
>
>
>
>
> *From:* RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] *On
> Behalf Of *Nick A Lucchese via RE-wrenches
> *Sent:* Thursday, January 18, 2024 9:50 AM
> *To:* RE-wrenches
> *Cc:* Nick A Lucchese
> *Subject:* Re: [RE-wrenches] Recommendation on DC Breaker
>
>
>
> The Siemens HNF361RPV is worth looking into. Quite affordable and reliable
> build quality without having to resort to Amazon. It first appears that
> it’s limit is 250 vdc but the footnotes indicate 600 once going deeper into
> the details. Obviously not a fuse though.
>
>
>
> Nick
>
>
>
>
>
>
>
> On Jan 18, 2024, at 7:59 AM, Jason Szumlanski via RE-wrenches <
> re-wrenches at lists.re-wrenches.org> wrote:
>
>
>
> Thanks, all, for the quick recommendations. I believe an isolator like the
> IMO is technically all that is needed since it is a current limited circuit
> and OCPD shouldn't be required, but the manual calls for a circuit breaker.
> That is probably just a semantics issue.
>
>
>
> On the other hand, the 1000V DIN rail breakers on Amazon are a dead cheap
> option and worth considering, too.
>
>
> 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 Thu, Jan 18, 2024 at 10:48 AM Jay via RE-wrenches <
> re-wrenches at lists.re-wrenches.org> wrote:
>
> I’d use an IMO disconnect as you don’t have any current limitations.
>
>
>
> I think sometimes things get lost in translation.
>
>
>
> Jay
>
>
>
>
>
>
>
> On Jan 18, 2024, at 8:43 AM, Jason Szumlanski via RE-wrenches <
> re-wrenches at lists.re-wrenches.org> wrote:
>
> 
>
> I am installing an EG4 off-grid 3k inverter for the first time, and the
> manual requires a DC circuit breaker on the PV input. It will be a small PV
> array with adjusted max Voc around 280V @ Isc 10.6A.
>
>
>
> I'm looking for a cost-effective DC breaker and enclosure for this purpose.
>
>
>
> Jason Szumlanski
> Principal Solar Designer | Florida Solar Design Group
> NABCEP Certified Solar Professional (PVIP)
> Florida Certified Solar Contractor CVC56956
> Florida Certified Electrical Contractor EC13013208
>
>
>
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