[RE-wrenches] SMA 40 series DC disconnect

Wed Dec 14 10:44:30 PST 2016

Bill:

That is exactly my point.  Carports and ground-mounts do not need RS, but
any system requires safe means to disconnect DC.  So how do you accomplish
this with the 40 series?

Sure, using the DC connector is one way to disconnect the DC input to the
40 series electronics.  However, the service manual cautions against this.
Below is the verbatim text from the manual.

>From SMA Document SB30-77-1SP-US-40-AT-PU-SG-xx-11 Service Manual:

• If an external DC disconnecting switch is available, open the external DC
disconnecting

switch.

• If there is no external DC disconnecting switch, cover the PV modules
with opaque

material (e.g. foil).

• Ensure that there is no voltage on the DC conductors of the PV array.

• Wait five minutes before working on the inverter.

• Leave the *DC-in *connecting terminal plate plugged into the Connection
Unit and only

touch it on the black enclosure.

I was told that the term ‘foil’ is a poor translation from German, and
likely means a tarp.  In any event, this verbiage is quite unfortunate as
it precludes using the connector as a disconnect.  I wonder if there is
some criteria on what kind of connectors can be used as a disconnecting
means and which cannot.  I am sure it has something to do with ‘touch-safe’
requirements.  The DC connector in the 40 series may not meet this
criteria.  The external leads could possibly come free of the connector
body as they are just insert-connected.  I would be very reticent to send
out a technician to work on one of these without some serious consideration
of the implications.

SMA seems like they are interested in this conundrum and I am withholding
judgement pending receiving a response from them.  I just thought it very
curious that they moved the location of the disconnect in the DC power flow
scheme.   Seems to me like a fundamental change that flew under the radar.
See below for a rendering of the change in DC power flow:

Formerly:  PV------àIntegrated Disconnect----àchassis separation

40 Series:  PV ----àchassis separation------àIntegrated Disconnect

William

PS:  I remember wasting an entire afternoon in a conference room in San
Diego arguing with Fronius about the same concept.  They too insisted that
to service the IG series inverter one had to just tarp the modules.  Let us
please put that myth to rest once and for all:  Tarping modules is not
viable.

Wm

[image: Gradient Cap_mini]
Lic 773985
millersolar.com <http://www.millersolar.com/>
805-438-5600

*From:* RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] *On
Behalf Of *billbrooks7 at sbcglobal.net
*Sent:* Wednesday, December 14, 2016 7:40 AM
*To:* 'RE-wrenches' <re-wrenches at lists.re-wrenches.org>
*Subject:* Re: [RE-wrenches] SMA $0 series DC disconnect

William,

I’m not sure you meant to imply this, but carports and ground mounts do not
need any RS equipment unless you were to bring the dc conductors into a
building, which would not be smart.

The 2017 NEC allows connectors to be used as isolation devices for
equipment as long as the circuit current is below 30 amps, which it always
is on individual strings. I realize California will not be on the 2017 for
3 years, but it will make installations cheaper, not more expensive.

Electronics are destined to become a bigger part of PV arrays in the
future—and not just because of rapid shutdown requirements. It just makes
sense in building applications for many reasons. The keys will be cost and
reliability.

Bill.

*From:* RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org
<re-wrenches-bounces at lists.re-wrenches.org>] *On Behalf Of *William Miller
*Sent:* Tuesday, December 13, 2016 5:39 PM
*To:* RE-wrenches <re-wrenches at lists.re-wrenches.org>
*Subject:* [RE-wrenches] SMA $0 series DC disconnect

Friends:

I am taking a poll to see if any of you have noticed the change in the SMA
40 series DC disconnect as compared to earlier series inverters and how it
may be affecting your installations.  The DC disconnect is no longer in the
lower, connection box area, but in the electronics area.  This means it
will not de-energize the DC connections.  Certain jurisdictions will not
allow us to install this unit without an external disconnect.  The service
manual addresses the subject.

The Remote Shutdown Box unit may provide a means to de-energize PV sources,
but in a webinar today SMA claims it does not meet code, possibly in
regards to lock-out capability.  It actually looked viable to me, but that
is not based on any research.

Soon all or most building mounted PV arrays will require Rapid Shutdown.
This will add hundreds of dollars to the cost of an install, but safety is
safety.  What may sting is adding $400-500 of RS equipment to a carport or
ground mount where it may not otherwise be required.

SMA has concurred that the issue bears further discussion and I should hear
back from them soon.  In the meantime, I thought it might be useful to all
parties to see how much impact this change in design is having to other
installers.

Thanks in advance for any input.  I will report back on what I learn.

William Miller

[image: Gradient Cap_mini]
Lic 773985
millersolar.com <http://www.millersolar.com/>
805-438-5600
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