Backfeeding a "240V Delta with a stinger" [RE-wrenches]

[Peter Parrish]

John Berdner explains it well, and I also got confirmation off-forum. The
IEEE requirement relates only to the manufacture of inverters. I believe all
of the major inverter manufacturers have either hardware (e.g. SMA, Fronius)
or software (e.g. Xantrex) settings that can disable the neutral sensing
where appropriate.

- Peter

Peter T. Parrish, Ph.D., President
California Solar Engineering, Inc.
820 Cynthia Ave., Los Angeles, CA 90065
Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885
CA Lic. 854779, NABCEP Cert. 031806-26
peter.parrish at calsolareng.com 


-----Original Message-----
From: John Berdner [mailto:jberdner at sma-america.com] 
Sent: Tuesday, November 13, 2007 12:38 PM
To: RE-wrenches at topica.com
Subject: [Norton AntiSpam] Re: Backfeeding a "240V Delta with a stinger"
[RE-wrenches]


Peter/Wrenches:
 
The issue is a UL1741/IEEE1547 issue not really an NEC issue.
The new UL1741/IEEE1547 requirement says that you have to measure
voltages line to neutral when the neutral is present.
For a 240 Delta (stinger) configuration the inverter would need to
measure the voltages L1-N, L2-N, and L1-L2.
On the other legs the inverter only has to measure L2-L3, and L3-L1.
For the inverters on the L1-N-L2 legs you need to run a neutral to the
inverters.
For the inverters on the L2-L3 and L3-L1 legs you do not.

There is a simple jumper setting that tells the inverter to measure
line to neutral or not.
It literally takes 5 seconds to configure the inverter and then the
rest is automatic.
This is possible with all of the new Sunny Boy "US" series, i.e. 3000,
4000, 5000, 6000, and 7000.
 
Best Regards,
 
John Berdner
 
 

>>> peter.parrish at calsolareng.com 11/13/2007 11:25:32 AM >>>

We have two customers with 240V/3P service with one center tap (neutral
and
grounded). I understand how these work in a conventional (i.e. non-PV)
world. Assume for the purposes of discussion the center tap is between
legs
L1 and L2. The following voltages can be derived: 

L1-N 120V, 
L2-N 120V, 
L1-L2=L2-L3=L3-L1 240V, 
L3-N 208V

My question is, "With the latest NEC requirement of wiring grid-tied
inverters with a connection to neutral, how can we backfeed the L2-L3
or
L1-L3 legs? Are confined to the L1-L2 connection?"

I have been told that Fronius might have a workaround by resetting a
jumper
(I'll look into this) but the question still remains.

Since we have two customers with this situation, and one job we have
already
started, any help would be greatly appreciated.

- Peter

Peter T. Parrish, Ph.D., President
California Solar Engineering, Inc.
820 Cynthia Ave., Los Angeles, CA 90065
Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885
CA Lic. 854779, NABCEP Cert. 031806-26
peter.parrish at calsolareng.com 



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