Another reason to dislike tray cable [RE-wrenches]

[William Miller]

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
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"Every decent man is ashamed of the government he lives under."
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