You really don't think 2017 is any better? You'll get no argument from me on the fundamentals you've described. I'm just curious how you would have the code improved. Personally I think it is a lot closer to reflecting the reality that you've described above. Is it the term 'functional grounded' that bothers you? I'm curious what you'd propose to replace it. 'Ground referenced'? For what it's worth I'm pretty sure the First Draft said 'Reference grounded' and for some reason they decided that was unclear.
A key operational characteristic of an ungrounded source (whether DC or AC) is that a single fault to ground will not cause current to flow. To a large extent this increases rather than decreasing safety.
A second operational characteristic is that for the purposes of insulation breakdown the voltage of any point within the source is not necessarily limited to the peak value of the line to line voltage. This makes it possible to read higher than expected voltages when using a high impedance meter, but is not likely to have safety consequences.
A third characteristic is that a single OCPD on one leg of the source cannot interrupt fault current if there are two ground faults both within and outside the source.
The "functionally grounded" array associated with a non-isolating inverter can produce fault current in the event of a single ground fault within the array.
So on point 1 it behaves like grounded rather than ungrounded.
The voltages at any point within the fg array (while the inverter is operating) can never exceed the peak AC line voltage plus the line to line DC array voltage. In fact it will always be equal to or lower than the peak AC line voltage or the DC line to line voltage, whichever is larger.
So on point 2 it is closer to grounded than to to ungrounded.
If there is a ground fault within the array, and the GF detector in the inverter does now work or the array is disconnected from the inverter input, a single OCPD on one leg of the array output will still be able to prevent fault current in the array unless there is a second GF at the same time.
Again, more similar on point 3 to a grounded array than to an ungrounded array.
IMO the biggest difference between fg and solidly grounded is in the details of point 3.
When it comes to the design and installation of SPDs, the details of point 2 are the most important. It affects the practical voltage thresholds of the SPD components.
. I would limit it to just two options, solidly grounded and ungrounded. All the requirements for the testing for insulation failure or ground fault by the PV system are, to me, completely separate functionality to the system grounding itself. But with the addition of the term "functional grounded” an attempt has been made to combine the ungrounded array with ground fault and insulation failure testing and create a new kind of system ground. I don’t think we were doing it right before when treating GFDI equipped arrays as solidly grounded and I still don’t think we are doing it right in treating “functional grounded” as anything other than ungrounded. The PV industry is just scared silly of calling anything ungrounded because of possible AHJ pushback.
