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

Thu Jan 18 11:39:15 PST 2024

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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