Grounding diagram is attached with questions

Re: Grounding diagram is attached with questions

Here is how I would interpret your diagram as applied to the NEC:

If your "Off Grid Setup" is connected to the same AC distribution system as the utility by way of a transfer switch it is not a "Stand Alone System".
It is not an "Interactive System" unless it can "sell" to the grid.

Your house is grid tied. Your utility AC distribution system is grounded. Unless the "Off Grid Setup" is isolated from your utility's "Electrical Production and Distribution Network" your "Solar Photovoltaic System" is grid connected and the solar AC grounding should be common to the utility AC grounding system with a single AC neutral bonding point. If the utility and the solar AC system outputs are completely isolated, each one will require it's own Neutral to Ground Bond.

Whether they are isolated or not, NEC 250.58 requires both systems to be connected to the same grounding electrode(s). "They shall be considered as a single grounding electrode system in this sense."
They must have a minimum size conductor based on NEC 250.66.
NEC 250.53(D)(2) requires a "Supplemental Electrode" for under ground water pipe.
NEC 250.104 (B) requires bonding "Other Metal Piping" to the grounding electrode system.

The "can of worms" opens when you look at the battery system's DC ground connection requirements (NEC 250.166) and neutral bond. The large battery cables can require a large "grounding electrode conductor". NEC 250.166(C) specifies "...that portion of the grounding electrode conductor that is the sole connection to the grounding electrode shall not be required to be larger than #6 copper wire..." (This is the murkey part. It is vague and some AHJs will interpret this very differently. I'm not looking at the newest version of the NEC so this may have been recently cleared up.)

NEC 690.47(C) requires that both AC and DC systems be bonded together either:
(1) with seperate grounding electrodes which are then bonded by a conductor sized for the larger of AC or DC grounding conductors.
or
(2) connected to the same grounding electrode with seperate conductors sized for the AC or DC system which they serve.



In short, you should probably run a "grounding electrode conductor" sized per NEC Table 250.66 from your utility service entrance to a new "grounding electrode" (ground rod) placed at, and connected to, the DC side (however you or the AHJ chooses to interpret the DC bonding requirements) of your "Off Grid Setup".


Alex Aragon

Re: Grounding diagram is attached with questions

ok that's a little clearer. i would still add the rod at the solar equipment area and bury at least 1 ft down in the outside dirt a bare #6 copper wire to tie the solar ground rod to the utility ground rod with the proper rod connections. although the pipe is convenient i don't recommend using it due to lightning aspects as this aspect you want to keep outside of your home in the ground where it belongs.

now this i didn't make myself clear on as the underground tie from the utility ground rod to the pv ground rod is what i said would be optional, but do understand that the nec requires that ground lead go along with the pv leads and into the home. if you were to tie the pv ground rod to the utility ground rod that 2 paths would be created to ground and that isn't recommended by me. the one with the pvs is required, but not hearing this from me i'd disconnect it at both the pv and solar equipment and just use the underground rod to rod tie later after any inspectors have already approved the system. remember that you can only tie the pvs one way or the other and underground with rod to rod is best, but the code requires a connection that travels with the pv wires.

i do recommend the burial of ground wires to be at least 1 ft down, but soil type and conditions may interfere with such a requirement. this is to minimize any possible damage to the wire from digging or natural occurrences. there aren't any guarantees damage to the ground wire will not happen in the ground, but the efforts you make there can minimize any chances of damage. an example might be to put small rocks or large gravel just above the wire and then continue to throw dirt onto the rocks to allow grass or other small vegetation to grow. if growing larger vegetation like bushes would mean the roots could surround and possibly push through the wire thus breaking the wire. one could encase the wire in pvc or something similar, but the wire itself aids the contact with the ground and increases the effectiveness of the ground. one possibility would be to increase the thickness of the wire to lessen the possibility of breakage, but copper wire is soft so no matter how thick it is breakage is still possible.