[RE-wrenches] DC Discos for Enphase

Matt Lafferty gilligan06 at gmail.com
Tue Sep 14 11:48:03 PDT 2010


Stir away....
 
Modern locking module connectors serve as DC disconnects for
micro-inverters. This point was alluded to in the Code Corner sidebar, but
not addressed in detail. It takes a little dance along Route 690 to drive
the point home to OCD-afflicted AHJs... But it's right there...
 
The simplest dance steps generally start with 690.14(A). This clause
specifically says disconnects don't have to be suitable as service equipment
and must comply with 690.17. 690.17 requires disconnects to be manually
operable switches or breakers that meet a host of requirements. And then
there's the exception, which throws all that out the window... Or off the
roof, as the case might be. (Exception: A connector shall be permitted to be
used as an ac or a dc disonnecting means, provided that it complies with the
requirements of 690.33 and is listed and identified for the use.) Listed and
identified as a PV connector meets this requirement. 
 
As your AHJ is quivering with OCD discomfort... Quickly flip to 690.33 to
send him/her into full-on convulsions... 
 
690.33 requires connectors to be polarized, noninterchangeable with other
stuff on the premises, guarded live parts, latching or locking, require a
tool to open, 1st make/last break grounding member and... Either be rated
for interrupting current without hazard to the operator OR require a tool to
open and marked "Don't open under load". 
 
Demonstrate your compliance to the AHJ this way: Flip your module over, grab
both connectors, plug them into each other, yank on the wires to demonstrate
that a tool is required to open the connector, and flick the sticker-tape
labels that say "Do Not Disconnect Under Load". Hand the connection to your
AHJ. Make hm or her check it out closely. While he/she is examining the
connection, reconciling in their own head the irrational concept that a
disconnect doesn't have to be a switch here.... Turn the module to face the
sun and point out to them that they are now holding an energized dead short.
Just for fun :)
 
If they can't wrap their head around the concept, take them over to your
work truck. Pull out a skilsaw. Show them the nameplate amps and discuss the
power of the tool. Way more watts and higher voltage than your module. Carry
the thing over to a live receptacle, plug it in, squeeze and hold the
trigger, pull the plug out of the receptacle. Happens every day with all
kinds of tools and appliances. There's no label on the cord or receptacle to
say you can't... 
 
Now compare this to your module connectors to demonstrate how much safer and
more effective the locking, labeled connectors are. Buried up there behind
the modules and all. Where only a qualified person can get to them. Where,
in the event of an emergency, shutting down the ac circuit reduces the
maximum potential current to one module. No matter how bad the fault is or
where it's located. Which is the lowest possible unit of energy in a modern
PV system. Can't get much safer than that!
 
Hope it didn't take too long to fall asleep...
 
Matt Lafferty

gilligan06 at gmail.com

 

  _____  

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of
SOLARPRO at aol.com
Sent: Tuesday, September 14, 2010 10:19 AM
To: re-wrenches at lists.re-wrenches.org
Subject: [RE-wrenches] DC Discos for Enphase


Howdy Wrench  
I don't try to stir things up, but I was just wondering last night as I fell
asleep reading the latest issue of HomePower magazine (# 139), if anybody
else caught a chill when they read this in the Code Corner (highlighted in a
box):
 
"Both microinverters and microinverters attached to PV
modules in the field or in the factory that have any exposed
DC single conductor cables are required to meet all of the
NEC's DC wiring requirements. These may include Section
690.5 ground-fault detector requirements, DC and AC
disconnect requirements (potentially handled by connectors
listed as disconnects), and inverter DC grounding-electrode
requirements."
- John Wiles
 
 Which begs the question: Are <any> module connectors currently listed as
disconnects?
 As well as: If DC voltages for each disconnect are less than 48 V, would a
simple  switch suffice, should the poor hapless installer run into an AHJ
with OCD?    
 
 
Patrick A. Redgate
AMECO Solar, Inc.
Serving Solar California
Since 1974
7623 Somerset, Blvd.
Paramount, CA 90723
562-633-4400
www.solarexpert.com <http://www.solarexpert.com/> 
www.amecosolar.com <http://www.amecosolar.com/> 


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