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

Wed Aug 8 18:58:23 PDT 2001

Hi Chris,

What you describe will basically work (maybe a little modified) but I would 
advise a different course. The set up as you describe will not allow net 
metering. The inverter system would sit there, batteries full, waiting for 
an outage. When the outage comes, the transfer switch senses power loss, 
and flips to the inverter side. Everything has lost power for at least a 
half second as the transfer switch senses and trips. this defeats another 
major advantage of the system, that is with the inverter you can set it up 
so that the power never drops out.

Here's how I would set this up.

Power from utility comes into main breaker panel (existing). ALL breakers 
are removed from this panel, and put into TWO sub panels.

Sub panel 1 is the REALLY critical loads. This sub panel is always powered 
through the inverter.
Sub panel 2 is powered through a MANUAL transfer switch. Power can be 
supplied to this panel either through the inverter or by the utility.

What this does is ensure that if he is not there, and the power goes out, 
he doesn't deplete his batteries. If the power is out, and he want the pool 
pump (say) to run, he turns off any breakers in sub panel 2 that he doesn't 
want to run (or leaves them all on) and then flips the transfer switch.

The AC1 feed is from a new breaker in the original main circuit panel. This 
lets him net meter and charge from the grid.

If he's absolutely set on having all the loads on one panel, then eliminate 
sub panel 2, put everything on sub panel 1.

Hope this makes sense.

Hope you're well in Montana.

Jeff

Jeffery D. Wolfe, P.E.
Global Resource Options, LLP
A Woman-Owned Limited Liability Partnership
4 Kibling Hill Road
P.O. Box 51
Strafford, VT 05072
800-374-4494 Toll Free
802-765-4632 Phone
802-765-9983 Fax
global at sover.net
http://www.GlobalResourceOptions.com

----------
From: 	Chris Daum[SMTP:info at oasismontana.com]
Reply To: 	RE-wrenches at topica.com
Sent: 	Wednesday, August 08, 2001 5:28 PM
To: 	'RE-wrenches at topica.com'
Subject: 	Grid Tie 240 VAC w/ transfer switch? [RE-wrenches]

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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