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

[Daryl DeJoy via RE-wrenches]

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@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
> 
> 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 

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

[William Miller via RE-wrenches]

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

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