Another reason to dislike tray cable [RE-wrenches]

Mon Apr 21 14:50:08 PDT 2003

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Hey William,

This method works well for me for that very reason:

http://home.earthlink.net/~clrwater/

Allows you to use MC connectors but go right into a J -Box with only
one KO per 4 MC wires (for 3/4" NM - More for 1" NM).

jc

>Friends:
>
>I am bidding an off-gird installation.  The customer purchased his
>equipment from a well known mail order outfit.  He has mounted his 8 Sharp
>165 modules on two fixed, pole mount racks.  I need to connect the Sharp
>modules to the Outback PV combiner.  Each module is a separate feed to the
>combiner, since the system is 24 volt, nominal.  I can't just run the tray
>cables to the combiner because 1, they aren't long enough and 2, there is
>no hardware I know of to bring the tray cables into an enclosure.  The tray
>cables with MC connectors are meant to connect to another MC connector. If
>I cut the MC connector off to feed the lead into a J-box, I void the
>warranty of the module.
>
>Here's the only way I can see to connect these modules up:  I provide a
>J-box on each pole with 8 tray leads hanging out of the bottom, each with
>an MC connector.  To do this, I need to spend $192.80 and lots of time.
>
>Below is an "ÄSCII" CAD drawing, if it doesn't get hacked up by line wrapping:
>
>
>
>-------------------------------------
>Module plus -----> >----Gland nut-| box ---splice-------THHN--|----\
>Module plus -----> >----Gland nut-| box ---splice-------THHN--|----\
>
>               conduit-----combiner
>Module neg  -----> >----Gland nut-| box ---splice-------THHN--|----/
>Module neg  -----> >----Gland nut-| box ---splice-------THHN--|----/
>
>-------------------------------------
>
>For each mounting pole I need to provide a J-box.  In each J-box I need to
>bring in 9 leads (4 modules with plus and minus and a ground).  I need 8
>gland nuts (Arlington LPCG50, $1.10 each) on the bottom of each J box.  I
>can't use a standard metallic Nema 3R box because by the time I find one
>with 8 existing KOs or room to add enough KOs to total 8, it would be huge.
>  So I need an 8X8X4 plastic J box (Carlon E898N, $24.00).  Then I need to
>purchase 8 prefabricated tray cables with MC connectors ($14.00 each).  I
>cut each one in two and install one end in each gland nut.  Once in the
>J-box, I need to get my leads over to the combiner.  I run PVC conduit from
>each J-box to the combiner.  If I put the combiner on one of the two poles,
>the tray leads from the J-box on that pole might be long enough to reach
>the combiner, but the leads from the other pole are not.  I need to splice
>the tray leads (the ones in the gland nuts) to some THHN.  I could use wire
>nuts, but I prefer a terminal strip ($24.00).
>
>Here's what this will cost:
>
>2	J-boxes		24.00	 48.00
>8	MC cables	14.00	112.00
>16	gland nuts	 1.10	  17.60
>1	terminal strip	24.00	 24.00
>
>Total				 211.60
>
>If instead of the infernal tray cables, I had J-boxes on the modules, I'd
>run 1/2"non-metallic flex and THHN from the module terminals straight to
>the combiner.  Cost:
>
>16	1/2 NMLT connectors	1.00	16.00
>6	feet NMLT flex		1.38	 8.40
>
>Total					24.40
>
>I would transition to 1/2 or 3/4 PVC and run right into the combiner.  I
>don't count the cost of the PVC in either scenario.
>
>Plus, with tray cable, I have multiple splices in the feed from each
>module, half of them outside of an enclosure.
>
>Where's the savings or reliability with tray cables?  Is there an easier,
>better way to do this?
>
>
>William Miller
>
>
>PS:  I am halfway through my first "top down"job using conduited wiring.
>It's a bit of a pain in the ass to use flex, but I have developed a
>technique that will become easier with practice, and it looks very solid.
>I will post pictures as soon as I can.  Contrast this with the Sharp
>modules on the neighbors house.  The prevalent view from the ground of the
>Sharp installation is of the gap between the modules and the roof.  You can
>see the spider web of wire hanging down, in spite of many wire ties used.
>The first Frisbee or ball that hits the roof will tempt some kid to use a
>pole to dislodge it-- and the MC connections.  Lets hope that pole is non
>conductive!
>
>WM
>
>
>
>
>
>__________________________________________________________________
>William Miller
>Miller Power and Communications
>PO Box 50, Santa Margarita, CA 93453
>Voice :805-438-5600     Fax: 805-438-4607
>email: wrmiller at slonet.org
>http://millerpowerandcomm.com
>License No. C-10-773985
>_____________________________________________________________
>Compatibility:
>Word processor: WP10
>Spreadsheet: Quatro Pro 10
>CAD: Microstation 95, DXF, Visio 4.1T
>_____________________________________________________________
>"Every decent man is ashamed of the government he lives under."
>                                     H. L. Mencken
>__________________________________________________________________
>
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--
~~~~~~~~~~~~~
Jeff Clearwater
Village Power Design Associates
Sustainable Energy & Water Solutions for Home & Village

877-SOLARVillage
PO Box 764
Boonville, CA 95415

61 Baker Rd
Shutesbury, MA 01072
413-256-6777, 413-825-0372 (Fax)
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