M-C branch plugs: Legal? Safe? [RE-wrenches]

Bill Brooks bill at brooksolar.com
Mon Feb 4 21:16:17 PST 2008


Mark,

You are correct. With few exceptions, paralleling plugs can only be used on
small inverters smaller than 3kW and cannot be used on 95% of crystalline
silicon arrays larger than 3kW. The Shell SQ-175 with the 20-amp fuse rating
no longer exists. With the 15-Amp fuse rating modules on the market today,
one string--one fuse if the array has 3 or more strings. I have never liked
paralleling plugs because many installers who use them do not understand the
design implications.

Bill.

-----Original Message-----
From: Mark Frye [mailto:markf at berkeleysolar.com] 
Sent: Monday, February 04, 2008 8:33 PM
To: RE-wrenches at topica.com
Subject: RE: M-C branch plugs: Legal? Safe? [RE-wrenches]


I am starting to be a bit interested in the discussion regarding
battery-less vs. battery.

What is the difference between having a hugh AC grid on the other side of a
transistor in an inverter and having a big battery on the other side of a
transistor in a charge controller.  Are the charge controllers so different
from the inverters that they can be expected to put current into the source
circuits? In a fault?

I don't really see how the batteries matter here.

Isn't this really about, generally, depending on the math, that when you
have three or more strings you should have individual string fusing per the
SMA white paper.

Perhaps someone could help clarify this for me.

Thanks,

MPF


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