[RE-wrenches] Supply Side Tap Overcurrent

[Steven Lawrence]

Ryan,

I agree with you 100% with the caveat that it's a straight grid-tied PV system.  A battery-backup system is a bit different.  Loads are being transferred from the main service panel to the backup load panel.  When there's no sun, the loads on the backup load panel are drawing from the grid.  The feeders now have to be sized to handle the existing main service panel and the new backup load panel.  In this scenario, theoretically 160A could be coming in on feeder cables rated for a 100A service.

Steven Lawrence

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Message: 1
Date: Wed, 31 Mar 2010 16:29:20 -0700
From: "Ryan LeBlanc" <ryan at naturalenergyworks.com>
To: <re-wrenches at lists.re-wrenches.org>
Subject: Re: [RE-wrenches] Supply Side Tap Overcurrent Protection
Message-ID: <FCD090A6D57E4B7B9EC92EF6B1FB8DCD at RJLPC>
Content-Type: text/plain;	charset="us-ascii"

Steven,

A Line Side Tap, by nature, allows us 100% of the Service Entrance Conductor
Ampacity.  This typically ~equals Main Breaker rating, but is regardless of
the Main Breaker rating or size of Loads, it's about the conductor.  NEC
recognizes that our systems produce power, not draw it, so downsizing the
Main would have no effect on the size of a Line Side Tap.  

Corrected PV output is considered continuous, so if you have 100Amps worth
of conductor, 100A worth of Loads (Coming), and 100A of Solar (Going), we're
still considered square on that service conductor.  Doesn't matter what the
draw is in the panel, the remainder of energy goes out the meter.  If you
downsize the main, you are just missing out on that much load capacity.

Downsizing Main breakers only assists Load Side connections, obviously by
increasing the Main Panel to Main Switch ratio for 120% Rule math.        

Check out: Solar Pro SP2.4 Article "Can We Land: Means and Methods of
Utility Interconnection." (LeBlanc/Yates)
Available Free online at SolarPro's website.


Ryan J. LeBlanc
NABCEPT Certified Solar PV Installer
Santa Rosa, CA
Cell: 707.591.1950
Direct: 707.536.9839
ryan at NaturalEnergyWorks.com
http://www.NaturalEnergyWorks.com