I just came back from a call back on a system we did last year. Problem?
Bad wire nut connection on the AC side. It it was a pump, so it took
several amps.
I still agree with August though, its not the wire nut; its not doing
the connection right.
This particular connection did not have enough copper stripped back so
it had insulation in the connection. This would be a problem with any
connection.
I've seen every type of connection fail at some point, almost always due
to installer error.
Regardless of the connection type, you have to do 2 things:
1) Strip the right amount of wire back (not too much, not too little)
2) Tighten the connection fully, and then a few minutes later, retighten
it, because stranded copper especially, seems to creep and loosen.
The internal arcing to the spring described by SMA, would only happen in
an improperly made connection IMHO. The spring shouldn't be the
conductor, the direct contact of wire on wire should be the primary
connection, and the spring is just mechanically holding that connection
in place.
Its amazing how otherwise knowledgeable NABCEP certified installers I've
worked with don't know some of the basics, like how to make a good
connection with a wire nut. We all need to be schooled by some good old
regular electricians on an annual basis IMHO. We could teach other a lot.
R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760
On 6/25/2014 11:12 AM, August Goers wrote:
Hi All -
We have been using outdoor Ideal brand wire nuts (the blue ones packed
with waterproof gel/grease) for all of our residential DC side splices
(typically #10 wire) for 10 years now and have never had a single problem.
If the installers properly strip the conductors and follow the
instructions I feel that these wire nuts make very robust connections. We
always do a good pull test after twisting the wire nut on. I would never
recommend standard wire nuts without the grease and have seen these fail
numerous times during inspections of systems installed by others.
Insulated terminal blocks also work well but don't have that nice
waterproof grease in them to help avoid moisture issues. You can wrap them
with a good splicing tape to help keep moisture out but the cost for these
connections is significantly higher than wire nuts:
http://solutions.3m.com/wps/portal/3M/en_US/EMDCI/Home/Products/Catalog/~?
N=5433135&rt=c3
Normally I error on the robust conservative side of the installation
spectrum but in this case it sounds like I may not.
Just my $0.02
Best, August
-----Original Message-----
From: RE-wrenches [mailto:[email protected]] On
Behalf Of William Miller
Sent: Wednesday, June 25, 2014 8:40 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] AFCI disturbances.
Richard:
Possibly. I think I prefer din mount connector blocks. However, if a wire
nut can arc internally a connector block might also. I am still wondering
about this concept.
William
Miller Solar
On Jun 25, 2014, at 6:09 AM, [email protected] (Richard L
Ratico) wrote:
William,
Would UL listed crimp sleeves be an acceptable substitute where you
would otherwise use wirenuts?
Dick Ratico
Solarwind Electric
--- You wrote:
Bob-O:
When you say verboten, what does that mean? Not kosher? Frowned upon?
Disallowed by law???
I am quite curious about this subject. Here is what I have learned so
far:
This is a unique case where we are replacing 3 dead SMA U series
inverters with 2 US series inverters. The U series seem to all be
dying at about 12 to 14 years of age. We have about a dozen of these
to swap on our calendar and expect more. It may be that to do this
right requires that we pull new wire from the arrays. This makes the
job a lot more expensive.
We have never used a wire nut on a PV lead until this project. It's
not that we disapprove of wire nuts in general, it is because we know
that if we were to use them regularly we would eventually have failures
and call backs.
We allow only one splice in a PV lead: between the cable provided by
the manufacturer of the module and a bulkhead mounted MC4 connector
direct to THWN in conduit
(http://millersolar.com/MillerSolar/practices/PV_wiring/PV_Cable_wirin
g/_PV_
Cable_Wiring.html).
We checked the manufacturer's listing and the wire nuts are rated for
600 volts. We do use wire nuts on AC circuits, such as switch and
receptacle circuits in a power room.
A tech at SMA told me that wire nuts "arc internally to the spring"
causing the AFCI faults. I am not aware of any process of "internal
arcing." To me, arcing means, as per the dictionary definition: "a
luminous bridge formed in a gap between two electrodes." The same
tech told me to solder the leads and apply shrink tubing. I don't
believe this is an approved method. By the way, we have spliced leads
on both US series inverters and only one is exhibiting AFCI
disturbances.
I do favor mounted terminal blocks, either screw or tubular type. I
need to check if the Amp model we stock are 600 volt rated.
I was told by another representative from SMA that on a ground-mount
system it is legal to disable the AFCI protection.
I will be troubleshooting this job tomorrow and I will let you all
know what I learn.
William Miller
--- end of quote ---
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