Ungrounded PV

Re: Ungrounded PV

As far as I know--NEC would allow to pairs of solar arrays to be carried in a single conduit/cable tray to two separate PV controllers (say two 5kW arrays and two independent 5kW inverters). One inverter is negative ground (+600 wrt ground) and the other has a hot to ground short that popped the 1 amp fuse causing the second array return to be at -600 VDC (worst case, Voc-cold)...

I am not saying that this is the worst thing in the world--Just from my experience, if I designed a system with +/- 600 VDC power lines, it would be difficult to justify sharing the same conduit with 600 VAC rated insulation. I asked Wiles directly--and he avoid the question.

I am listening. I just am not always at a full computer+keyboard (doing some stuff from my phone).

Regarding #59:

It seems to me that if charge controllers for OG systems used the same (dual ammeter) GFP method that ungrounded (non-isolated) GT inverters use, this whole issue might be solvable, without the issues Bill keeps harping on. The GFP device would be powered by the PV and would open both sides of the PV circuit if it detected a ground fault. The battery side and the battery grounding connection would be unaffected. As far as the NEC is concerned, it probably needs some language to clarify if the PV circuits in such systems should be treated as grounded or ungrounded (I think it should be the latter, even though I don't think the same for GT systems.) But it's already permitted by the current code.

I have never needed to look at "precision" DC paired leakage detection circuits (or DC paired +/- circuits such as done with AC GFI systems and a simple current transformer)--But I have mentioned in earlier posts that such circuits as being easy or cheap to implement (DC current Hall Effect transistors tend to drift a fair amount over a few minutes of time--The other "obvious" way would be a pair of current shunts and use the sense leads to drive the disconnect circuit). It could get a bit messy--You would need to sense at the destination (GT inverter or Solar Charge controller that there was a miss-match of current flow in the +/- current lines, then send a signal back to the solar array to pop a dual pole breaker/relay of some sort. Not a very elegant solution.

Yes--I could see the PV circuits as being at least "labeled" as ungrounded circuits.

And, the current DG GFI system with a sense breaker/fuse--The location of the return to earth fault is dependent if the fault occurs at the array (where you can drive some current through the ground) vs a fault near the destination (where a return to earth fault simply bypasses the fault detection fuse/breaker).

Regarding the DC Off Grid System side--Ryan "Halfcrazy" from Midnite tested my suggestion that a Hot to Earth fault will result in ground reversal on a DC power system (i.e., typical off grid system with battery bank/inverter for stored energy) which would deliver "excessive" current through a return wire (no breaker/fuses on grounded neutral return wires)--depending one where the fault would occur. So--It has been confirmed that such a setup is "not ideal".

And, again from Ryan:

Quote from: jtdiesel65 on January 04, 2012, 09:50:04 AM

In terms of the classic hardware, I'm reading this as

if I tie my ground bus to negative bus, it will defeat the gfp capability of the classic since the classic won't be able to detect voltage differences between ground and (-). Is that correct? Other than that, there is no impact to the classic. Is that also correct?

That is correct. And is most likely how you would find my system with a big fat wire connecting battery negative and earth ground.

In of my previous posts here--I asked what you guys would think if an AC Mains system for a typical North American Home we put a 1 amp fuse between the White Wire Bus and Earth Ground (instead of the standard Earth Bond at the mains panel, and at the pole transformer to its own ground rod)... Would that be safe (assuming we don't have a double pole breaker on the distribution transformer--that would be similar to how we wire DC Battery banks and Solar panels today).

And would anyone want the entire power to their home (and the three or four other sharing the pole transformer) want to have their power killed if there was a "simple" hot to earth fault anywhere in those homes (in the DC GFI system, a hot to earth fault anywhere in the system--Solar panels, charge controller output, battery bank, loads, MS Inverters, etc.--Would pop that detection fuse/breaker).

-Bill