# Solar Panels Shorting Out and Backfeeding



## Rick (May 10, 2002)

"You also need to install a 10A breaker on each string in the combiner box. This prevents the other 3 strings from backfeeding to one should it short out."

This recommendation was made to me by a poster. I am not in a position to install breakers at this time.

Can anyone give me an example of what could cause a panel to short out? What would be the result of panels back-feeding into one that had shorted out?

Thanks,

Rick


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## 12vman (Feb 17, 2004)

If you have a blocking diode installed at each panel, you probably wouldn't have to worry about "Back Feeding". 

It would take a lot of panel to kick a 10 amp breaker in this situation. Panels usually don't short. They'll open.


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## ace admirer (Oct 5, 2005)

agree, each panel must have a diode, if not any panel that is shaded more than the others will act as a load instead of a source. that would cause a condition that could be called back feeding and could look as a "mild short"


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## TnAndy (Sep 15, 2005)

Most newer panels 50 watt and above come with bypass diodes built in so if part of the panel is damaged or shaded, the power flows around that section so all power isn't lost from the panel.

Learned that this past weekend from a NABCEP certification class.


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## Rick (May 10, 2002)

Thanks.

I did a google check and these panels are said to have an "ultra reliable bypass diode".


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## wy_white_wolf (Oct 14, 2004)

The indidivdual breakers are to protect you, the structure, and the system should one of the wires from the panel to the combiner box short out. From what I understand you are running about 15 feet of wire from the panels before it reaches the combiner box. Nice little strings exposed to elements and other causes for shorting out.

Blocking diodes and bypass diodes are different and serve different proposes. Bypass diodes will not prevent backfeeding. 

Blocking diodes mounted in or on the panels will not stop the other panels from backfeeding into the wire should one wire short out. Without protection the one shorted out wire will recieve the total amperage from all the other stings of panels in the system.


PV and NEC: Suggested practices


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