Backfeeding existing circuits

2 Posts
Apr 14, 2010 01:54 pm
Backfeeding existing circuits

As a result of adding propane for heating and cooking to my home, I now have 2 high-amp 240V circuits unused in my main circuit/distribution box.  As long as AC disconnects were in place, would it be kosher(ie, legal per NEC) to connect PVstrings with Enphase grid-tie only microinvertors(240V).  It seems doable and would save on wiring/box/etc. costs to just connect the AC line from the Enphase strings to the existing 60Amp circuit wiring via a disconnect/junction box.  Since no power is supplied when the grid is down, if disconnects were there, I don't see why this shouldn't be possible, but I don't know the ins & outs of this.  On the surface it seems like a good way to save $(since the Enphase are expensive, but suit my purposes otherwise). Also, if OK for NEC, does anyone know if it's legal in NH?  If you're a NH PV installer, send me your info.
351 Posts
Apr 14, 2010 05:49 pm
Re: Backfeeding existing circuits

While you can reuse the wiring, you will need to replace the breakers with 15 amp breakers.

The wiring will be greatly oversized. So if it isn’t going real close to where it needs to be, I think I would abandon it in place and just make some new home runs with more appropriate sized wire

The first ac connector in each branch circuit (a connector in the enphase supplied connector cable) is approved as your ac disconnect.  However, your local building inspector or your local utility may require some sort of separate AC disconnect closer to your breaker box, because they are used to seeing it on other solar systems. If either of them wants the additional disconnect, it will save both time and money to put it in, rather than to argue the point.  When you go in for the permit, discuss the issue with them.
2 Posts
Apr 14, 2010 08:34 pm
Re: Backfeeding existing circuits

Thanks a lot for your input. I did not know the first Enphase unit had an AC disconnect other than the anti-islanding feature.  Given the location of the unit relative to the main distribution panel, I suspect you may be right about the local inspectors and past experience with them  has taught me you are spot on about it being easier to just go along than to try to get them to understand something to which they're not accustomed (they sure didn't like the vent free propane 99.96% efficient fire log set I had put in my fireplace - even though it had a flu).
I was actually thinking of combining branches for the Amp rating of the current circuits, but since there are 2, just putting in smaller fuses is probably easier and cheaper - thanks again.  -  RML

Disclaimer and Disclosure

The Alternative Energy Store, Inc reserves the right, within its sole discretion, to refuse or delete any posting or portion thereof, or terminate or block the access to this forum.

The opinions and statements posted on this forum are the opinions and statements of the person posting same, and do not constitute the opinion or act of the Alternative Energy Store, Inc (AltE). The Alternative Energy Store, Inc does not endorse or subscribe to any particular posting. No posting shall be construed as the act or opinion of the Alternative Energy Store, Inc.

Click here for BBB Business Review

McAfee SECURE sites help keep you safe from identity theft, credit card fraud, spyware, spam, viruses and online scams
Desktop Website | Mobile Website


Click on an icon to share! If you don't see the method you want, hover over the orange "+".


What can we do to help you?

Please enter a summary
Sorry, the copyright must be in the template.
Please notify this forum's administrator that this site is using an ILLEGAL copy of SMF!
Copyright removed!!