[RE-wrenches] Supply Side Tap Overcurrent Protection

[Hans Frederickson]

Ryan,
Agreed that the line side tap does not necessitate any change in the size of
the main... we got off track a bit there. Thanks for straightening that out.

The initial question from Nick was whether he could _avoid_ a line side tap
or service upgrade. He wants an exception to install load side PV source
breakers larger than 20% of the main by showing that the sum of the
residential load calc and the PV source does not exceed 120% of the bus
rating. I don't see how this could be accepted by the AHJ since 690.64(B)(2)
speaks only of the amp ratings of source overcurrent devices and does not
allow an exception based on actual loads.

When adding loads to a service, it is common practice (when in doubt) to
perform a load calc to show that the service rating isn't being exceeded...
Perhaps Nick heard from someone who was trying to creatively apply that
practice to size a PV source. Since the 120% limit is a frequent problem, I
think if there was a legal workaround as easy as showing a load calc, we
would all be aware of it by now.

-Hans



-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Ryan LeBlanc
Sent: Wednesday, March 31, 2010 4:29 PM
To: re-wrenches at lists.re-wrenches.org
Subject: Re: [RE-wrenches] Supply Side Tap Overcurrent Protection

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



Today's Topics:

   1. Re: Supply Side Tap Overcurrent Protection (Steven Lawrence)


----------------------------------------------------------------------

Why can't you do a line side tap and downsize the main breaker?  Use a 60A
main disconnect for the line side tap, and use a 60A main breaker for the
service panel.  That's similar to what I did except I downsized the 200A
main to a 150A. This also allowed a manual interlock kit in the main service
panel that can be fed from the backup load panel.  

Steven Lawrence

______________________________________________________

Date: Wed, 31 Mar 2010 08:13:10 -0700 (PDT)
From: Nick Soleil <nicksoleilsolar at yahoo.com>
To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
Subject: Re: [RE-wrenches] Supply Side Tap Overcurrent Protection
Message-ID: <342120.66732.qm at web44904.mail.sp1.yahoo.com>
Content-Type: text/plain; charset="us-ascii"

    Downsize the main breaker?  I would if I could, but the customer only
has 100 Amps now, and the solar is fed with two breakers, a 30A and a 40A.
So to be under 120Amps, I would have to size the main to 50 Amps, which may
be problematic.
    I can also do the line side tap, but had heard that a load analysis may
be accepted instead.  The loads of the house will never use more than 100
Amps.  I am wondering if any codes or white papers detail that option.  

 Nick Soleil
Project Manager
Advanced Alternative Energy Solutions, LLC PO Box 657 Petaluma, CA 94953
Cell:   707-321-2937
Office: 707-789-9537
Fax:    707-769-9037



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