[RE-wrenches] Conductor Sizing for Supply Side Connection

Wed Feb 27 16:41:14 PST 2013

Alan,

Thanks for the clarification. I believe you and Jeremy are talking about
the exception listed on the last paragraph of 705.12(D)(2). I've never used
that rule but it is good to know about. When we do battery backup we
typically route the critical loads through an external transfer switch
rather than through the battery inverter but this definitely has the
potential to open up doors and potentially reduce equipment cost.

Best,

August

August Goers

Luminalt Energy Corporation

1320 Potrero Avenue

San Francisco, CA 94110

m: 415.559.1525

o: 415.641.4000

august at luminalt.com

*From:* re-wrenches-bounces at lists.re-wrenches.org [mailto:
re-wrenches-bounces at lists.re-wrenches.org] *On Behalf Of *Allan Sindelar
*Sent:* Wednesday, February 27, 2013 4:08 PM
*To:* RE-wrenches
*Subject:* Re: [RE-wrenches] Conductor Sizing for Supply Side Connection

August,
The 60A breaker is intended to allow grid power to pass through to the
loads in excess of the inverter's stand-alone output. The point of 705.12
(moved in the 2011 NEC from 690.64 (B)(2)) is to differentiate between load
pass-through current and sell current. The amount of current fed into the
grid is (4500/230 =) 19.56A, while the amount that can be taken from the
grid and passed through to the load is much greater. If you were limited to
a 40A breaker in order to maintain 120% of a 200A main bus, you'd be prone
to nuisance trips under large cumulative loads.

Allan

*Allan Sindelar*
Allan at positiveenergysolar.com
NABCEP Certified Photovoltaic Installer
NABCEP Certified Technical Sales Professional
New Mexico EE98J Journeyman Electrician
Founder and Chief Technology Officer
*Positive Energy, Inc.*
3209 Richards Lane (note new address)
Santa Fe, New Mexico 87507
*505 424-1112*
www.positiveenergysolar.com

On 2/27/2013 4:23 PM, August Goers wrote:

Jeremy,

Good point. Even under the 2008 NEC 690.64(B)(2) you can install up to a 40
Amp breaker on the load side as long as it is on the opposite side of the
input feed per 690.64(B)(7). Garrison, do you need a 60 A breaker?

I haven't used this product myself, but if the continuous output power is
indeed 4500 W then you'd be fine with a 25 or 30 A breaker.

Best,

August

*From:* re-wrenches-bounces at lists.re-wrenches.org [mailto:
re-wrenches-bounces at lists.re-wrenches.org] *On Behalf Of *All Solar, Inc.
*Sent:* Wednesday, February 27, 2013 1:50 PM
*To:* RE-wrenches
*Subject:* Re: [RE-wrenches] Conductor Sizing for Supply Side Connection

There is an exception in NEC2011 regarding the point of connection. This
may not apply, but you could avoid the supply side.  4500W / 240V = 18.75 x
1.25 = 23.4A, well under the 120% rule. reference 705.12(D)(2)

Jeremy

All Solar

CO,USA

----- Original Message -----

*From:* Garrison Riegel <garrison at solarserviceinc.com>

*To:* 'RE-wrenches' <re-wrenches at lists.re-wrenches.org>

*Sent:* Wednesday, February 27, 2013 2:15 PM

*Subject:* [RE-wrenches] Conductor Sizing for Supply Side Connection

Wrenches,

On an upcoming job we have a Xantrex XW4548 interconnecting with a 200A
service, and I’d very much appreciate some advice if y’all are willing.

Since the inverter output OCPD is required to be 60A we are looking at a
supply side connection, and I have two questions:

1.       Before the point of interconnection the inverter output circuit
will first pass through the XW Power Distribution Panel and inverter
bypass, which is essentially a 60A breaker.  The service disconnect for the
supply side connection will also be fused at 60A.  Does the 120% rule apply
to the conductor between these two OCPDs?  Or since this is a supply side
connection in accordance with 690.64(A), 690.64(B)(2) will not apply? [this
AHJ is on the 2008 NEC]

2.       Can anyone recommend a reliable insulation piercing tap
connector?  Or would you recommend something else entirely for a
residential supply side connection?

Thanks in advance,

Garrison

847-677-0950

Solar Service Inc.

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