Bonding a large solar array

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lile001

Senior Member
Location
Midwest
We are putting a solar array on the roof of an apartment complex. Each subarray will consist of 15 panels connected with microinverters to a circuit in that apartment's subpanel. The arrays will be adjacent to one another on the roof. Total of about 60KW of solar panels. Apartments all are fed out of one meter bank.

Obviously we have to bond the panel rails. But to where? Should the array rails be discontinuous between each subarray, so that the bonding wire from a subarray feeds back to only the one panel? Or should all the rails be connected together, since they are all right next to one another? I am worried that if we bond all the rails together on the roof, and also have bonding wires going back to the apartment subpanel ground bus, that we are creating a giant ground loop on the roof. Each microinverter communicates over powerline carrier to an internet gateway. Will such a ground loop cause communication problems? This certainly would be the case in audio equipment where ground loops are a big deal. Is a ground loop more likely to function as an antenna, picking up lightning voltages? Most all the grounding systems I've done (a lot) have always been some kind of star arrangement where everything bonds back to a single point. There may be a ground grid, or a loop under the building, or what have you, but all the equipment ground wires star back to the same point.

How would you approach panel and rail bonding?
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
My intial advice is don't bond the arrays together. All you really need is equipment grounding which can be done via the circuit back to each apartment subpanel. If you need to have more than one unit's inverters on the same physical array, it's acceptable to bond the array and panels to the EGC for just one of those circuits, to reduce ground loops.

Depending on your code cycle and their awarenees of code, your AHJ may or may not cause trouble by requiring an electrode for the arrays. 2008 required one, 2011 deleted the requirement, 2014 put back a (stupider, IMO) requirement for an auxiliary electrode.
From the standpoint of ground loops and lighting, the requirement is unhelpful and possibly dangerous, so hopefully your AHJ won't bring it up or you can talk them out them out of it.

If the building is in a lightning prone area then it should probably have a lightning protection system. I believe it's a mistake to try to address lightning as an installer. Either consult a professional or don't worry about it.
 
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