[RE-wrenches] DC Discos for Enphase

[Bill Loesch]

Matt,

I like your writing/presentation style. I like the content even more. Excellent analogy.
I _will_ try this, given the opportunity.

Bill Loesch
Solar 1 - Saint Louis Solar
  ----- Original Message ----- 
  From: Matt Lafferty 
  To: 'RE-wrenches' 
  Sent: Tuesday, September 14, 2010 1:48 PM
  Subject: Re: [RE-wrenches] DC Discos for Enphase


  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
  www.amecosolar.com




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