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_wiring/_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 ---

