I got zapped! Where is the voltage coming from?

[qrper]

Well, where to start?

I added an extra 2kw to the battery based solar array. Now I have 6 kWp of solar going to the batteries.

The wire leading from the pv to the batteries was over 20 years old and to top it off wasn't even the correct wire to be buried. I know, my bad... but it did work for all those years.

Long story short. I replaced my old home-brew combiner box with a mid nite solar 12 circuit box. Disconnected the old wire and rented a trenching machine to put in brand new #2 gauge aluminum wire. This was direct burial, no conduit needed or used. This wire runs about 150ish feet to a junction box mounted on the side of the house. From there, it's spliced into #2 gauge copper wires that go to a Midnite solar MNDC175 where the Classic 150 sits atop. The chassis is grounded to the main and single ground of the house.

So, when I went to remove the heat shrink seal on the now presumed dead line, I got knocked on my @^#!
There was no, and I mean NO voltage across the wires. All breakers between me and the Classic 150 were opened. The wire from the pv was dead, cut off as a matter of fact.

Yet, if you measured from EITHER wire to earth (NOT GROUND) there was 70ish volts AC lurking on either cable. NOT between the two and not to ground, but only to earth. Connect one meter probe to a cable, jam the other into a pile of near by dirt and whoa! There be 72 volts.

If you connected the two cables together, and measured from that point to earth, you got voltage. Inside the garage where the classic lives with the batteries, measuring from either cable to ground and nothing. Of course there's wasn't any piles of dirt in the garage, so I wasn't able to try that test.

Gang.... any one have any idea where the AC voltage was coming from? I had the inverter running, the negative leads are connected to the whizbang in the MNDC175 the classic sits on.

I finished the connections to the new cable, and everything fired up without issue. Now, I'm overloading the Classic 150, but I figured during the winter months, the extra PV would be worth having.

mike

[ClassicCrazy]

Do you have grid AC to your house ?
Maybe bad ground on the transformer on that ?
There used to be stray voltage issues on farms because of the way some of those transformers were wired.

Larry

[boB]

Can you make a simple drawing/schematic of what is going on including any AC in the system ? 

Also, show the breakers that are open.

[qrper]

Do you have grid AC to your house ?
Maybe bad ground on the transformer on that ?
There used to be stray voltage issues on farms because of the way some of those transformers were wired.

Larry

Yes, the grid is connected. At the time, the grid tie was operating and the trace SW5548 inverter was up and running.

mike

[qrper]

Can you make a simple drawing/schematic of what is going on including any AC in the system ? 

Also, show the breakers that are open.

I'll see about hand drawing something up.

mike

[boB]

Well, the Trace SW5548 inverter does have a common mode filter on the AC that might be part of this or maybe nothing to do with it at all.

Each line and neutral too I think has a small capacitor to GND (chassis).  This makes a capacitive voltage divider where you can measure half the line voltage (close to 70 VAC) between two points.   I remember getting a tingle from this I think if the ground is not connected to chassis.

I may be remembering that *slightly* wrong on how it had to be wired but that voltage divider can definitely give around 60 to 70 VAC and tingle a bit.

I would have to draw that up to get it straight but this might be it.    Or not.