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

[Peter Parrish]

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 

-----Original Message-----
From: Bob Ellison [mailto:reellison at gmail.com] 
Sent: Monday, November 12, 2007 7:24 PM
To: RE-wrenches at topica.com
Subject: [Norton AntiSpam] Re: Heating oil vs. electric heat [RE-wrenches]



Electric is more expensive, hands down. In this area, (Northern New York)
electric is pushing .18 (18 cents per KWH) generally you have to double the
figures on the energy tags in the stores to get close to the true operating
cost of appliances.

Bob Ellison


On 11/12/07, Joel Davidson <joel.davidson at sbcglobal.net> wrote:
>
>
> Would a wrench in heating oil territory please tell me if it is cheaper to
> heat with oil than electricity?
>
> I was told:
> 138,000 btu per gallon of fuel oil at $3.00 per gallon.
> 3,413 btu per kWh of electricity at $0.11 per kWh.
> Efficiency of oil = 78%
> Efficiency of electric furnace = 95%.
> Cost per 1,000,000 btu from oil = $27.73.
> Cost of 1,000,000 btu from electric furnace = $33.94.
>
> Thanks in advance,
> Joel Davidson
>
>
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[Non-text portions of this message have been removed]


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