Wiring or Connection Issue and Advice on Conduit
Sorry for the length of this, but the meat is in the first three paragraphs. Two basic questions; finding the problem and questions regarding best pratice when running conduit 300 feet from PV to CC & batteries.
We have a small solar setup at our remote cabin. Description is below. Thursday we dropped by to check on things. We had been absent a couple of weeks and left the PV disconnected as we are into rain and lightning season, though there's no recent evidence of either. The MN SPD'S are viable, the LED's light up. However when I reconnected the PV cable and toggled the breakers "On" the charge controller did not wake up. After flipping all the breakers off and back on there was no change. First I connected the CC to the batteries. The CC cycled up okay. Closing all input breakers from PV to CC was next. Nothing; no apparent input from the PV. Time of day 1030 (AM) with bright blue sky. Normally the CC would have been busy working for a couple of hours already.
Voltage at the CC input was a fluctuating 11 to 16 volts. A puzzle. ? A voltage reading at the pole mounted PV array disconnect breaker found 99 to 102 volts. That coincides well with the panel specs. Using a clamp meter on the + wire from the series connected panels produced a 0.00 current flow. Same reading of zero current and around 100 volts taken after the breaker with breaker closed. Zero current should indicate the absence of a short circuit in the 300+ feet of wire from the PV to power pole at the cabin end. Right?
However at the top end of the PV wire run there was virtually zero volts; 165 mV was read after leaving the breaker on the input side of the CC off for a while. With that breaker closed I would get something above 12 volts. I assume that is feed back from the batteries. ??
History & Equipment…
Three 208 watt pole top mounted, serially connected PV panels. Because of tall pines the array is about 320 feet down a slope with the PV at the bottom and the cabin at the top. Midnite Solar Kid controller at cabin end. Copper #2 AWG wire. At the PV there is a MN combiner box, not for combining anything but to provide an easy method to disconnect from that end.
At the cabin end there is a post mounted box with another MN-EPV breaker used as a disconnect. I call that post my power post. The power post is about 12 feet from the cabin. I use a flexible 10 AWG cable from power post to cabin as a means to disconnect the PV input when lightning is likely. The cable gets rolled up at the cabin; a big jump for lightning to cross.
That cable connects to yet another MN-EPV just before the MN The Kid charge controller. Another breaker is on the output side of the charge controller, to the batteries. The output wires connect to a pair of solid copper buss bars in the battery box. The 8 golf cart batteries are connected in two parallel series strings for 24 volts. Those are parallel connected via the buss bars with a type T in each + wire. The inverter connects to the buss bars via a type T fuse and a large DC rated breaker; the breaker for convenience as a disconnect.
The system went into service in summer 2009; now 7 years old. Same batteries. A couple of years ago we had major lightning damage. The original FM60 was toast and replaced with MN The Kid. The VFX3524M was rebuilt. The power pole disconnect cable was installed post-lightning strike.
Back in 2009 money was tight with all the construction going on at once. I got a very good deal on a full 500 foot spool of the #2 AWG copper, plus a remnant of about 200 feet. Yes, I used a splice block in one of the wires. Until now everything has been working as expected, hoped for. Maybe the splice was a mistake? It is a metal, tin plated block with twin set screws on each end. An adhesive lined heat shrink tube was used over the splice. Wires and splice are inside pvc conduit. Maybe another mistake was placing the splice inside the conduit instead of inside an accessible box? I know more or less the position of the splice in the run, but it means cutting apart the pvc conduit. Carefully cutting.
Conduit details, maybe another error. I trenched and buried the first 115 feet, from the power pole down the upper section of the hill. From that point the remaining 185 feet was left exposed, laying on the ground. Some reasons for my doing that... #1, the degree of slope. I did not feel I could control the trencher on it. #2,the rocks on and in the ground and large pine roots. #3, there is a dip, a small ditch that has to be crossed right near the PV pole. PVC was flexible enough to follow the contour.
The splice is not in the buried section of conduit.
Post-lightning I began to think that not burying the conduit was a bad idea. I also now wonder if I should have used EMT. Could I, should I, have buried EMT instead of pvc?
I suspect the problem may be at the splice. Any other ideas? Once I find why power does not make it up to the point of use what would be the better / best solution to the conduit if what I did was poor practice?
If EMT or other rigid conduit should be used can it be used above ground at the dip? Supported of course, with some sort of a trestle; whatever. Or should it be bent to follow the contour of the earth?
If buried conduit is best all the way, digging an NEC approved depth is going to be extremely difficult because of the aforementioned rocks, roots and slope. All 185 feet by hand. At 8800 feet elevation it does require some effort for those not acclimatized. Fortunately I feel I could dig a trench, but maybe only 6 inches or so. The original installation was passed but the inspector was not having fun walking his overweight self around.
FWIW, the flooded GC-2 batteries don't seem to mind being left disconnected from the PV for a couple weeks at a time. They still work well enough for their age. I would like to replace them with a lithium type as those seem to do well with being left in a partial state of charge for extended periods.