Grid Tie 240 VAC w/ transfer switch? [RE-wrenches]

[Jeff Clearwater]

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Hi Chris,

I would recommend a yet different approach.  On a dual SW5548 system 
(120/240 Volt) that I did at Sirius Ecovillage that fed 2 main 
apartment panels (each 125 A Subpanels with 16 breakers each plus a 
few 240 volt loads),  I installed 4 GENTRANS, 2 on each panel.

That way the customer has the best of both worlds and you don't have 
to rewire the whole panel or create a new critical loads sub.  Every 
breaker in the house can easily be put on the Traces or all can go to 
the utility or any combination in between.  The 4  Gentrans cost me 
$800 wholesale and installation is a snap.

I use the hardwire GENTRANS - model number 30408 that has 6 15 amp 
circuits and 2 20 amp or you can combine two for a 240 volt load with 
6 singles left.   http://nbmc.com/gentran/30408.html  (I believe 
GENTRAN is now offering all 20 amp circuits or at least you can 
request that)

In fact I use this scheme for all my SW based intertie installations 
now.  It gives the ultimate transfer switch distribution flexibility 
for the lowest cost and installation time and can be used on 
retrofits or new construction equally well.  If you have a generator 
running into your Trace's then you also get to use the full 60 amp 
pass throughs and power the whole house with the gen/solar in gen 
support mode quite easily.

For intertie systems that insist on being in off-grid mode for the 
solar loads, this system all also allows the user to fine tune the 
loads so that the incoming matches the outgoing without much cycling. 
I could always keep my batteries at between 60-90% by just watching 
the Tri-metric and adding or subracting a circuit or two as needed 
just with a throw of a switch.

If you do follow this approach make sure your grounding system is 
thorough and you size your neutrals right so you don't get neutral 
current on the grounds.  Also make sure to provide a 30 Amp input 
breaker for each GENTRAN.  This system works especially well for dual 
SW 120/240 volt systems.

Cheers,  Hope that helps!

Jeff Clearwater
Ecovillage Design


>Dear Wrenches:
>
>My client's system is in California; he has two Bergey XL 1's on order, and
>has two Trace SW4024's and six 120W modules.  He is in a place with rolling
>power outages and wants back-up (vis a vis eight of the Surrette S460
>batteries).  His power is rarely out for more than an hour at a time.  His
>site offers excellent sun and winds, with 15 to 18 mph averages.
>
>But, he doesn't want a separate sub-panel for his important loads.  Has
>anyone done a grid-tie with a transfer switch (located before the main
>electrical service panel), where one side of the transfer switch is from
>utility power, and the other leg is 240VAC from the inverter's output?  My
>client wants total back up not just dedicated loads, and says he'll "power
>down" in the event of a power failure (and yes, I've cautioned him that if
>the grid fails, it would be easy to max out his inverters). There is no
>fuel generator integrated into this system.
>
>I've talked with a nice fellow from Asco (http://www.asco.com) about
>whether their transfer switches would work for this application.  We both
>think it would--but know of no one who's tested or tried this.
>
>One thing I'm uncertain about, code-wise, is feeding the utility input into
>the AC 1 "in", from the utility side of the transfer switch (like, with a
>separate 60A circuit breaker).
>
>Anybody got any ideas or experience with this type of system?  I'd
>appreciate any advice you could offer.
>
>Chris Daum
>Oasis Montana Inc.
>406-777-4321 or 4309
>406-777-2632  fax
>http://www.oasismontana.com
>
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-- 
~~~~~~~~~~~~~~~~~~~
Jeff Clearwater
Ecovillage Design Associates
780 Poplar Ave
Boulder, CO 80304
Community and Village Scale Renewable Energy Systems
303-546-0460, jeffc at ecovillage.org, clrwater at earthlink.com

Council Member - Ecovillage Network of the Americas 
http://www.gaia.org/secretariats/ena/
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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