[RE-wrenches] Flexible stranded Connectors
Glenn Burt
glenn.burt at glbcc.com
Wed Apr 30 12:54:49 PDT 2014
Why yes they are copper, thanks for asking.
Well the list would not let me attach the cut sheet – so here is a link I
hope works
http://www.greaves-usa.com/pdf/Shoo-Pin%20Color%20Sheet.pdf
-Glenn
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Allan
Sindelar
Sent: Wednesday, April 30, 2014 11:32 AM
To: RE-wrenches
Cc: Positive Energy, Inc.
Subject: Re: [RE-wrenches] Flexible stranded Connectors
William, Ray and Wrenches,
You're not alone on this issue. We faced it and did not come up with a good
resolution nearly two years ago. This is a Wrenches writeup from June 2012
that never got posted:
Four Sunny Islands and one Radian Outback
Fine Stranded Cable and Sunny Island Inverters
This is a brief overview of a project that involved the desire to use fine
stranded UL compliant Cobra X-Flex Cable for the battery 48 Volt DC input on
a quad stack Sunny Island system. Traditionally we have installed standard
doubled up #2 THWN for each Positive and Negative terminals on the Sunny
Island. A single 2/0 THWN cable is very difficult to install because of the
tight bends through the 1½” metal flex conduit, and to get away from
doubling up #2 we came up with the idea of using fine stranded cable.
This system involved four Sunny Island inverters and one Outback Radian
inverter. In this case we actually downsized from the standard 175 amp to
smaller 125 Amp disconnects for the 5kW Sunny Island inverters. This was
done because having an additional Outback inverter in the system meant that
we would need to install a whole system shunt in order for the master Sunny
Island to properly maintain Battery SOC. The shunt we intended to use was
rated 1000 Amps, but not rated for continuous duty. With four 125 Amp
breakers for the Sunny Islands and two 175 Amp breakers for the Radian this
would total 850 Amps as the highest potential for the 1000 Amp shunt. This
also meant that we could use single 1/0 fine stranded conductors for the DC
inputs to the Sunny Islands. We went ahead and ordered around 70 feet of
fine stranded 1/0 Cobra X-Flex. [Followup note: the 125A DC breakers have
worked well with no nuisance tripping in this residential application.]
The bright idea of using fine stranded cables quickly became more of a
headache then an actual great solution to small conduit and difficult
bending radiuses. It stated clearly in the Sunny Island installation manual
that the terminals were not rated for fine stranded cable. Thus we decided
to go ahead and post the subject on the Wrenches List and the solution to
the problem is easily solved by installing a ferrule. I browsed through some
of the links supplied by the Wrenches list of companies that manufactured
ferrules. I found 1/0 ferrules that were about 7/8” long to fit into the
terminal lugs of the Sunny Island Inverters. I began looking at the outside
dimension of the ferrules and the inside dimension of the terminal lugs and
it turned out that the ferrule was slightly too large by around 1/64” to fit
into the terminal lug before tightening down the terminal screw. I had never
installed a ferrule before and assumed that it just meant sliding the wire
into the ferule and sliding it into the terminal lug and tightening down the
terminal screw. My assumption that the ferrule would not actually fit into
the terminal lug may have been totally wrong due to the fact that once
crimped it may have actually fit anyway. Without a proper ferrule crimper
and with the thought that the ferrule would not fit I began looking for
another solution to the problem.
I started browsing the Ilsco catalog and found pigtail adapters as the
solution to the issue. These adaptors would crimp onto the fine stranded
cable and had a pigtail of coarse strands that would go into the terminal
lugs of the Sunny Island Inverters. Thinking that I had found the solution
to the problem I went ahead and scheduled the electrical aspect of the
system and on site gave my right hand man the instructions for the pigtail
adapter installation. During the installation he suddenly came to me and
said that he could not install the pigtail adaptors because on the inverter
it said “use copper conductors only” and the tails of the pigtail adapters
were aluminum strands. I then looked directly at the terminal lugs on the
inverters and the actual rating stamp was listed as CU9AL. I thought that as
the terminal lugs are rated for aluminum, there should be no problem. I
decided to call SMA tech support to find out if I could indeed use the
aluminum pigtail adaptors. I spoke with Bill of SMA and sent him text photos
of the pigtail adaptors and also sent him a photo of the terminal lug
showing that it was rated for aluminum. He said that aluminum conductors
have a lot higher resistance and voltage loss, thus the inverter would not
be able to maintain accurate SOC for the batteries. I then suggested that as
the pigtail adaptors were only three inches long in total and the tail
itself was only one and a quarter inches in length, there could not possibly
be enough resistance and voltage loss for such a short length. He said that
he really did not know why I could not use them and would have to send the
information off to Germany for the SMA engineers to evaluate.
Being that this was off to the Engineers and we were on the job, I spoke to
my superior of the issue and was instructed to just go ahead and use the
aluminum pigtail adaptors and not worry about it. There could not possibly
be a reason not to use them being that the lugs themselves were rated for
aluminum.
About a week later Bill from SMA finally got back to me and said that the
engineers had finally got back to him. They said that the lugs on the
inverter had actually been modified and I could not use the pigtail adaptors
after all.
Now that the system is fully ready to go, pigtail adaptors and all. I have
began to lose sleep over the whole conundrum feeling that if anything were
to ever go wrong with those connections, SMA would not honor any warranty on
the inverters. Just the fact that anything could go wrong is unnerving
enough, warranty or no warranty.
What is the real solution to the now current issue? If I had a 1/0 ferrule
crimper I might try to actually go the ferrule route. I could look for
copper pigtail adaptors or use a different type of terminal adapter that had
a flat blade terminal instead of wire strands.
It looks as though Glenn's suggestion of the Greaves Shoo-Pin would work
well, as long as it is copper. Is it, Glenn? Also, Jim's Allied bootlace
ferrules would also resolve this, but at a pretty steep price considering
how often it would be used.
Here are two relevant posts from John Berdner of SolarEdge (formerly of SMA
America) about this issue in February 2013. These are more focused on SI5048
conductor and breaker size:
Ryan:
Not sure what is in the manual now but...the lugs in the SI 5048U are dual
2/0.
We had to use parallel AWG #1 because we kind of painted ourselves into a
corner.
The breaker in the SI ended up being 250 Amps, the conduit fitting was only
1.5" and the wire bending space was too small for a 3/0.
The only way to get enough Ampacity in a 1.5" conduit and that wire bending
space was to go with dual #1's.
The 250 Amp breaker was used just to get enough current for the very short
duration surges without tripping the breaker (12kW per SI).
If not for this a 200 A breaker would have been fine.
Note that the actual full power ampacity required for normal operation is
5kW @ 40 Vdc = 125 Amps continuous.
It is the high surge loads that require more current.
I run mine with a single 2/0 and we have never even come close to hitting
full power.
Worst case current is typically while charging, not when inverting, and I
set the current limit so that I do not exceed ampacity of 2/0.
In my experience it takes >= 14kW generator to drive a pair of SI's to full
power while charging
Best Regards,
John Berdner
Allan:
In my experience, the worst case currents occur during battery charging
following a deep discharge. (You should see a generator exhaust pipe at
night when charging hard – such a pretty shade of yellow/orange.)
The SI has parameters you can set to limit the maximum charge rates which
should solve your concern. This is found in SI Parameter #222.01 under the
Battery Settings menu
#222 Battery Charge Mode
No. __Name Description__Value Explanation ___Default value
01__ BatChrgCurMax__Charging current of the battery10 A
1200 A__1,200 A
I am not sure if this value is the sum of the SI currents or if this is
actually the value the inverters read off the external current shunt needed
for DC coupled systems. I think the SI uses the current shunt value (if
present) but I am not sure - Check with SMA Support to find out. If it is
the former then you would need to consider the Radian charge current and
subtract that off your maximum allowed value then enter that “net” value
into the SI’s.
As I mentioned in my earlier posts the breaker in the SI was selected to
match the short duration current versus time trip curves. Since the SI can
do very substantial surges (up to 12 kVA per inverter) the short duration
tripping characteristics were key. As I recall the breaker was actually 2
internally parallel AMS 125 (non-standard part from Eaton). See curve 252
(DC 25x) data on page 8 of the following
http://www.heinemann-electric.com/acrobat/ams-cata.pdf.
<http://www.heinemann-electric.com/acrobat/ams-cata.pdf> Not sure what
breaker is used in current SI production but the characteristics should be
similar to the above.
In normal operation the maximum continuous current will be the inverter
rating divided by minimum battery voltage. I ASS U ME this is where the 125
Amp recommendation for a SI5000 comes from (5000W/40Vdc). Never mind that
pesky 1.25 * the continuous current NEC thingy.
If you are using an external OCPD be sure to use a L
O
N
G time delay type
and compare the short duration trip characteristics of your OCPD to that of
the SI’s breaker. If your OCPD will trip “sooner” than the SI’s breaker you
may see nuisance tripping of your OCPD during high surge events. There
might be a parameter to limit the maximum discharge (surge) current but I
could not find it in my admittedly quick skim of the SI manual. If you do
not foresee very high surge loads (motor starting) this will not be an
issue. 48 kVA seems like one heck of a surge but, then again, I have not
seen the customer’s home.
Best Regards,
John Berdner
General Manager, North America SolarEdge Technologies, Inc.
William, the core issue of fine-stranded cables was brought out by John
Wiles about ten years ago. He wrote about the issue in a 2004 Home Power
Code Corner article that can be accessed here:
http://www.nmsu.edu/~tdi/pdf-resources/CC104.pdf.
Allan
Allan Sindelar
allan at sindelarsolar.com
NABCEP Certified PV Installation Professional
NABCEP Certified Technical Sales Professional
New Mexico EE98J Journeyman Electrician
Founder (Retired), Positive Energy, Inc.
505 780-2738 cell
On 4/30/2014 12:01 AM, William Miller wrote:
Ray:
Darn good question, especially since I will be doing the exact same thing,
*tomorrow*.
I have never been clear on the real problem. Fine stranded cables overheat
in the wrong lugs? Is this true for mechanical or compression?
Aside from code compliance, what is the best common sense approach to Sunny
Islands with fine stranded? Annual retorquing? Pin terminals? Solder
tinning the strands?????
I used to wrap thin copper sheeting around fine stranded just to corral the
strands. Is this a possible solution?
Thanks Ray for bringing up a question I forgot to consider.
William
Miller Solar
On Apr 29, 2014, at 10:48 PM, Ray Walters <mailto:ray at solarray.com>
<ray at solarray.com> wrote:
Hi All;
In order to avoid any of my work showing up in someone's slideshow of
horrors, I'm trying to find the correct way to wire 3 Sunny Islands with
Cobra X flex cable.
While it doesn't actually mention it in the SMA manual, a call to SMA tech
support confirmed my suspicions: the DC lugs in the inverter are NOT rated
for flex or fine stranded cable.
Both SMA and CED recommended I try Grainger's for crimp on adapters.
Grainger had no clue, and nothing came up in searches there.
>From a trade show, I have an ILSCO lug book, that shows a crimp on pigtail
adapter. It does not mention whether its flex rated though on the crimp
side of the adapter, as the adapter is used primarily to land over sized
cables into smaller lugs. (2/0 to #1, for instance)
The best I've found so far, is NSI, which makes sleeves, that are installed
around the wire, right in the connection:
http://www.nsiindustries.com/products/electrical/connectors/compression-conn
ectors/copper-compression/fsflex-cable-sleeve.aspx
I also found a Schneider white paper recommending sleeves with their lugs:
http://static.schneider-electric.us/docs/Circuit%20Protection/0515DB0301.pdf
So who has used these sleeves, and where do I get them?
The sleeves seem like a decent compromise, whilst the ILSCO pigtail adapters
are coming in at $40/ ea...... (ouch)
On the internet, I'm seeing several examples of X flex used directly (no
adapters) with the Sunny Islands, so are folks just blowing off articles
690.31(F) and 110.14, that specify the connector be rated for flex cable?
And finally, couldn't SMA use a lug that was flex rated?
For example, Marathon makes Class K rated mechanical Lugs:
http://www.marathonsp.com/NewRatings.html
I'd use THHN, but I really don't feel good about wiring the Heineman
breakers with that stiff a wire. I've cracked breaker cases
before......that's why the X flex is industry standard for off grid DC.
Thanks for your help,
--
R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760
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