On 10/9/12 6:13 AM, John W wrote:
Installers are here and in the process of installing a PV solar panel
system on my house for electricity generation. My question is about
how they should ground the roof rails.
Their plan is to: (1.) Run the ground wire from the roof rail system
directly to the ground bus in the house's main circuit breaker panel,
and NOT install any separate ground rods to ground the roof rails
directly to the earth.
That would be the normal scheme, and be code compliant.
Is that acceptable for lightning protection? (The concern is
lightning, not code conformance, because the town inspector will be
here this afternoon to insure code conformance.)
Do you have any other lightning protection? (e.g. air terminals and
separate grounding for them?)
This design seems less than ideal because the existing ground wire
from the house circuit breaker panel makes several small-radius turns
between the panel box and the ground rod. Plus it brings lightning
energy from the roof into the house and right into the circuit
breaker panel box if the roof gets hit.
Small radius turns aren't a big deal.. sure, they increase the
probability of flashover to something next to it, but presumably, what
it would flashover to (i.e. conduit or junction box) is also grounded.
Is a ground rod your only system ground? No Ufer ground?
There are two other things that I can think of that could possibly be
done, either alone or in addition to (1.) above:
(2.) Run the roof ground wire down to one or two ground rods driven
at a point that allows for the shortest, straightest possible ground
You could do that, but you'd need to bond all the ground electrodes with
AWG 6 or larger.
(3.) Run the roof ground wire down to the existing main house
ground rod that is bonded to the panel. (As a practical matter, they
would strip part of the existing ground wire insulation and connect
to that wire with a split bolt at a point about 18" above the ground.
Mmmm.. I don't know that a splitbolt meets code. The code allows
"approved compression connectors" so maybe it is.
That connection point would be code compliant, and would address your
concern about the bonding path being "through the box".
My preference would have been a cad weld, but I don't think that will
be possible because they aren't equipped for that.)
I plan to eventually run a full perimeter ground around the house and
bond it to my 3 or 4 towers. But I have not run it yet, because I
haven't installed my towers yet. I am planning to tie the perimeter
ground to the existing house ground rod, hopefully by cad welding, as
well as to my station ground.
Is (1.) above sufficient? Should they also do (2.) and/or (3.)
and/or something else?
Another option would be to let them just do (1.) now, and then later
when I install the perimeter ground, I could run another ground wire
from the roof rails to the perimeter ground.
Curious if you have any thoughts on grounding option 1 vs. 2 vs. 3
vs. a combination of them.
How have other hams who have solar arrays grounded the array?
The NEC rules (and similar.. NFPA 780 for lightning) are evolving fairly
rapidly for solar panels. Solar panels raise all sorts of complex
issues.. For instance, you can't turn them off.. if there's light on
them, there's power coming out.
Hoping for very quick answer to this question, because they guys are
here now and they need a decision today so they know where to run the
wires. (If you are reading this after 5 PM EDT on Oct 9, then you
don't need to spend any time replying, because it will be too late to
change the design.)
Thanks in advance to all you lightning and grounding experts,
John W2ID _______________________________________________
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