remote grounding

erne · November 2012

I am helping a neighbor build an off grid solar system for his home that has grid (200 amp service) but will not back feed solar into the grid. It will use a transfer switch that allows only one or the other systems to operate his home. System specs are 2 Outback 3624 inverters, classic stacked presently running to the well (40 feet) using #8 wire to the well head. The inverters batteries and associated equipment are housed in their own structure. My intent was to use the wire from the grid a/c box to the wellhead (120 feet) to feed the transfer switch with the solar. This wire turns out to be #12 copper. The #12 wire is run from the grid connection to the well (3 wires 220 volt)(2-110v hot legs,1 neutral) No ground wire from the grid, and has been running the well for a number of years. The well is now running on solar and will not receive grid electric.The intent was to use the abandon a/c wires to hook the solar to the transfer switch to run the household during outages and to help reduce the electric bill by switching to grid during heavy loads (laundry etc) The house is another 50 feet from the transfer switch and a/c disconnect, and is ran in aluminum and probably #4 or Larger.
Problem #1, Why was well running without a/c grounding. Was this a code violation? Is #12 wire sufficient for a 220v pump 100 feet of wire to well head plus 200 feet down to the pump? Wire size down well unknown at this time.
Problem #2, The inverters are grounded at power house to run the well. Can the inverters line 1&2 and neutral be ran without a ground to the transfer switch then to house system? Would this create a ground loupe and inter fear with the single ground neutral point in the house panel? Would I need to bring a ground from the transfer switch to the well and abandon the ground at the inverters? It looks like I need #6 or #4, 4 wire burial-able cable and abandon the existing system. This would also reduce the distance from the power house to the transfer switch to around100 feet. Which is correct? Any help?

Cariboocoot · November 2012

Re: remote grounding

Deep well pumps don't really need ground wires as they are submerged in water; instant grounding all around. It may be a code violation because the people who come up with codes don't always understand this.

Is the wire sufficient? Depends on the pump. But the lack of a ground wire between the pump and house does present a problem for using the inverters at the pump to supply emergency power to the house (that is the layout/intent, right?) I'm pretty sure leaving out this ground connection between the inverters and house would be a code violation, although it no doubt would work. Ground doesn't do anything until something goes wrong. Considering the distance between the two grounding points, I wouldn't worry about it. But if it has to be inspected, an AHJ just might.

For what it's worth, ground (literally) used to be used as a conductor in some wiring situations way-back-when. Frankly it didn't always work well because the resistance varied with te rain.

The actual wire size is another issue. If the specs are 240 VAC @ 30 Amps over 60 feet, 12 AWG is capable of that with

% V-drop. But as a rule it would only be allowed 20 Amps continuous in conduit if I recall correctly. If I've got those numbers confused, just work out the V-drop and Ampacity for the correct ones. Looks like you should replace the 12 AWG with 10 AWG to me, and then they'll want that ground wire in there. Again, the distance between grounding points should not present a ground-loop problem.

As always, others' opinions may vary and feel free to disagree.

remote grounding

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