# PV question



## one man show (Dec 20, 2010)

Heres the senario

I have a 100 amp meter socket over a one hundred amp fused disconnect. "existing" fuses at 80 amps. below that i have a new 100 amp panel backfed with a 30 amp PV 2 pole breaker at a single family residence. 
can we do it


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## woodchuck2 (Feb 27, 2008)

I am not picking up what your throwing down here, need a little better explanation. What is "PV"? Your back feeding a panel with this PV breaker?


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## one man show (Dec 20, 2010)

*pv*

Photovoltaic article 690 NEC


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## jamesgr81 (Feb 14, 2012)

*max is 20*

690.64(b)(2) 2008 NEC

The max rating of overcurrent devices feeding the panel cannot exceed 120% of bus rating. So max 120 amps feeding 100 amp panel. Since the fuse is 80 amps and the PV feed is 30 amps you are good to go.


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## 97catintenn (Mar 13, 2012)

Not without the POCO's approval. When the poco thinks that they have cut power from the line, you may still be sending power from your house to them, and that would be a safety hazard.


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## solar guy (Apr 9, 2012)

it would certainly work so i guess your going with about 9kw? or so? what type of inverter are you using? many of these inverters are built with safety trips when the grid isnt available ( ie, the utility is down for maintenance or repair) then the inverters will automatically shut down for that reason so as not to feed power to line that are thought to be shut off.


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## woodchuck2 (Feb 27, 2008)

Ahh, picked it up now. Thanks.


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## aptpupil (Jun 12, 2010)

97catintenn said:


> Not without the POCO's approval. When the poco thinks that they have cut power from the line, you may still be sending power from your house to them, and that would be a safety hazard.


a properly setup pv system has blocking diodes, or similar, in place to prevent feeding the grid with your solar power.


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## jamesgr81 (Feb 14, 2012)

*no backfeed*

Any listed solar photovoltaic inverter has to shut down on loss of utility power. No chance of backfeed. See 690.61 NEC 2008


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## 97catintenn (Mar 13, 2012)

and you have pv systems meant for houses that are not on the grid, that are listed. :whistling


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## jamesgr81 (Feb 14, 2012)

*yes*

If the PV system is not on the grid there is nothing to backfeed...

Any Utility Interactive Sysyem has to shut down on loss of utility power to comply. That was the OP's situation.

Wish I had a system that could allow me to go off grid!!


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## solar guy (Apr 9, 2012)

There are lots of those systems it just takes money


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## 97catintenn (Mar 13, 2012)

What if your system is generating more energy than you are using. Does your system backfeed then, or shut down?


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## solar guy (Apr 9, 2012)

Where do you live and are you going to maintain a grid connection? What are your power needs? How many kilowatt hours a month do you use. There are too many issues to just say yes ir no to that question


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## 97catintenn (Mar 13, 2012)

nevermind.


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## one man show (Dec 20, 2010)

*pv*

Many systems have a special meter (supplied by utility) that reads backwards and they ( the utility ) pay u. Here in Calif bay area PG&E installs this meter after final. and yes most inverters are utility interactive so that when the power is interupted they will shut down but only from the inverter downstream. everything upstream is still hot


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## solar guy (Apr 9, 2012)

Alot of places i dont know about where you live will allow you to put electricity onto the grid but they wont pay you for it you need a contract with them


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## solar guy (Apr 9, 2012)

If you want to go off grid ill show you how and tell you who to buy from thats no problem you can do inexpensively compared to grid power for the restof your life


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## one man show (Dec 20, 2010)

well they credit your bill monthly for the wattage you have run back through thier meter mainley you are consuming the power you produce its a small amount you actually contribute


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## smalpierre (Jan 19, 2011)

aptpupil said:


> a properly setup pv system has blocking diodes, or similar, in place to prevent feeding the grid with your solar power.


Blocking and bypass diodes are both on the DC side, has nothing to do with preventing the system from powering up utility lines when they are supposed to be dead.

Blocking diodes prevent current from flowing backwards. In a stand alone system with batteries if you didn't have them, the panels would turn into a load on the battery without them. They also prevent multiple sources circuits from feeding each other - such as when one source is shaded and would become a load.

The inverters handle shutting off power feeding to the grid when the utility lines lose power.


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