Wiring or Connection Issue and Advice on Conduit

Mountain Don

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.

 

Thanks everyone.

mike95490

PVC or EMT does not matter.   PVC, even the gray electrical, weakens under constant sunlight.
pulling a splice block into a conduit was a poor choice, going to be a real pain to check on it.

Try disconnecting the PV from the charge controller and then see what voltage is at the controller end of the PV run.

BB.

Do any electricians carry TDR equipment (aka "cable radar") for finding buried power line faults?

Time-domain reflectometer - Wikipedia

-Bill

Dave Angelini

BB. said:

Do any electricians carry TDR equipment (aka "cable radar") for finding buried power line faults?

Time-domain reflectometer - Wikipedia

-Bill

I have and do use a 10$ sony AM radio. You can go between the source and destination and often find a change in sound of a weak station. Or, go between stations.  The Inverter should be powered up with a decent  load on it. Turn the CC on and start hunting.

The propane delivery guys also have a device for hunting a gas line (the wire they put next to the plastic). Good Luck Don !

Raj174

Don,
Is it possible to just pull in a new cable using the one that was spliced?

Rick

BB.

Neat idea with the AM radio--If there is a "short"--I would suggest a 40 watt light bulb in series with the hot lead to the "shorted line"--At least you can inject noise with faulting the inverter (a noisy device such as a CFL or possibly LED bulb might work even better--These tend to be "noisy devices").

-Bill

Vic

Mt  Don said,  "   ...   

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. ??   ...   "

Hi Don,

YES,  when the PV input breaker is open,  and the CC's battery breaker is closed,  there should be some voltage showing at the CC input side of the PV breaker,  and shown on the FM's display.   On many/most MPPT CCs,  this is because there is a fairly high value resistor across the CC's input relay.  This pre-charges the input capacitors,  if nothing else.  So seeing some fraction of battery voltage is normal with the PV breaker open,  and at night.

SO,  it does seem that the PV cables from the array disconnect must have an open.   This is better than a short,  as many MPPT CCs will toast if their PV input terminals are shorted to  the CC's negative buss.

Raj's idea of trying to pull  in new cable is good one,  and common practice,  when there is not a pull-rope in conduit.  The cable with the splice is probably the open,  but it may not have the mechanical strength to pull in a single replacement cable,  so probably would need to pull both out at the same time,  while pulling in two replacements  --  YES,  expensive.

Just my guesses,  Good Luck Don,    Vic

Mountain Don

Thanks for the comments, ideas. I may try to find the exact position with an AM radio; I have one of those up there, and lots of empty bandwidth.  I know more or less where it is... one of two positions about 30 feet apart. (I can tell from the previous lightning strike repairs. 

I may try to pull the wire and see what happens.  Yes, yet another error was to not leave a cord/rope in the conduit for future "whatevers."      This will be in a few weeks time unfortunately as previous, non changeable plans are in the way. 

BB.

Tie a pull cord (brand new, don't use old stuff that can break) when you old cable fit inspection/repair/replacement.

-Bill

westbranch

if you have to pull both wires out, why not pull 2 new ropes and pull the good cable back into the conduit...??

Raj174

Don,
It might be easier/cheaper to use the spliced cable to pull in just a pull rope. That way, there would be a lot less stress on the splice. Then use that rope for a new cable and another pull rope.

Rick

Wheelman55

Don. What size PVC conduit did you use?

zoneblue

Yeah thats a long way to pull anything if the conduit has any sort of fill factor. Many electricians use TDRs now a days, it ll tell you exactly how many feet from the cable end the fault is.  There are some homebrew TDR ideas floating around if have access to a oscilliscope. https://www.google.co.nz/search?q=tdr+arduino+diy

Joining underground cables is a bit of an art, basically involving crimps, and an appropriate sealant. You can buy patch kits, but, i would think that an inline crimp splice, some epoxy/silicone/3M 5200 and a couple layers of heatshrink would also work.

As for the lightening issues, with such a long cable, your certainly got your work cut out. A slow twist in the home run pair, SPDs at both ends, and textbook grounding and bonding will all be required.

Dave Angelini

Don's a good guy and we have spent some time together several times. 
I am going to bet that since there has been lightning involved that the defect in the wiring run is not where the splice is.

Why do I guess that?  Well, years of experience with lightning which in some ways is like hurricane season.
You don't reason with hurricane season!

mike95490

Use a submersible well pump splice kit, 4 lengths of goo lined heat shrink, made to be submerged

Dave Angelini

mike95490 said:

Use a submersible well pump splice kit, 4 lengths of goo lined heat shrink, made to be submerged

Or even better the heat shrink from Anchor rated also for salt water and spray.  I think Don did this or I am mixing him up....
How are the trees doing Mike?  The pond still full?

jonr

Interesting, looks like a TDR tester can be as little as $50.  (eg, VDV501-089 from Klein Tools).

mike95490

Hazels doing pretty good, pond is being consumed

Dave Angelini

Is that Bigfoot in the left of center in your pix above?
 Our pond was dry last summer the first time since the gold miners were here in the 1930's before WW2. Good this year! Fish too!

Mountain Don

We've not been ignoring the forum, per se, but we've been away, camping around various parts of CO, WY, MT and ID for the past 3 weeks+.

Just came back from the cabin where I spent 2 whole days investigating and repairing. I dug up the area where I knew the splice to be. It sure pays to photograph installations as they are being done.  I cut the PVC conduit carefully and pulled it apart, and found.....  drum roll... the splice was perfect. The heat shrink still shrunk and stuck in place like the day I did it. It was/is the type of heat shrink with adhesive inside.  But there was still no power making its way from the PV to the 325 foot distant charge controller end. 

Careful inspection of the conduit that was left above ground back in 2009 found a blown apart coupling. It was hidden under years of fallen pine needles. Inside I could see lots of black carbon. I disconnected the wires at the down slope PV pole and proceeded to pull the conduit downhill, off the wires. I made a few cuts and did it in 30 foot sections. FYI, I used a steel pipe cutter, the type you rotate around the pipe as you move the wheeled anvil closer to the cutting disc. Works good and reduces the risk of cutting into the wires. 

Right where the coupler was blown up I found a completely severed, burned, arc damage wire. Dave wins the cupie doll!  I continued and pulled the entire above ground length apart. One hundred and eighty five feet. No other damage to the wires was found although 2 more couplers were exploded just as before. FWIW the damage was in an area where the conduit dipped slightly before rising and then falling further down the slope. 

No pictures this time as I forgot the camera and my phone camera is non functional. But here are 2 photos from the previous lightning damage that took out virtually all the electronics in the PV system as well as the TV and anything with "chips" inside the cabin.  As a note of interest the previous strike and damage was on July 21, 2014. 

Previous damage photo...  Smallest conduit damage... Coupler side blown off.


... to one of the larger sections where the conduit was fractured and shrapnel spread all over the surrounding ground. . Nothing this time came close to this...


The bare copper ground wire is hidden. The other conduit is actually a seldom used, gravity feed water line used to extinguish fire. 

This time nothing was damaged anywhere, other than the hidden exploded PVC and the one wire. Two of the Midnite Solar SPD's had done some work as they were non functional as noted back in my OP. 

I dug up 30 feet of the buried line from the downhill end where it had been left above ground. No damage to any couplers. Also exposed 30 feet at the top end and there was no damage. Testing the wire from the break to the PV end revealed continuity was great. Ditto for continuity the other way, up the hill to the CC. 

I spent much of yesterday digging 185 feet of trench down the hill to the PV pole/array. Some 50 feet of that through a rock field. Fortunately the rock is a crappy volcanic pumice that succumbs easily to a pick axe. No basalt or other harder rock thank goodness.

So now all the conduit is buried. Now the new splice is in an above ground junction box. Now the repaired Midnite SPD's are installed at each end of the run. I have a spare and am thinking of installing it in the new junction box which is about the 60/40 point.  

Now the PV system is charging again when the suns shines.  Except that we are now in monsoon and lightning season and when we leave the cabin we disconnect the PV feed from the CC at the cabin end. 

Mountain Don

One more thing. July of 2014 the lightning strikes included three 60-70 foot tall Pondersosa Pines near the cabin. There were bark traces spiraling around the trunks as well as branches and bark littering the ground. Those three have died this year. The needles are half way to brown. Going by the woodpecker activity today the lightning may have made them less able to fight off the pine bark beetle. The next time we're up there I'll have to drop the three. They'll make great firewood in a year or two. 

Dave Angelini

Not happy about winning the cupie!
 Not even going to go there about the bark Beetles. It just makes me cry!
Good luck and don't save the good wine!
 Enjoy it now but keep being hopeful !

westbranch

good points guys but to add clarity to the issue:
 I believe you are talking about the Mountain Pine (Bark) Beetle Dendroctonus ponderosae  that is know to attack Lodgepole pine and Ponderosa pine as well as the rare White pine that grows at upper elevations, ie Colorado....  It has also been observed to have attacked Spruce trees in BC.
It has a cousin the Southern Pine Beetle Dendroctonus frontalis.
And finally  another (significant) cousin the Douglas-fir bark beetle Dendroctonus pseudotsugae found from California to mid-northern BC.
here is an interesting publication if interested ..http://www.barkbeetles.org/index.cfm.
for info on a specific tree search for the name, upper right... 
And for those with MPB as we call it,  read this and weep... http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2664.2010.01848.x/full...  It has decimated the L. pine stands locally!
enjoy

Mountain Don

Yes, that is the one.  We've seen way too many mountainsides and entire valleys with nothing but brown needled trees. And the years after hillsides of grey sticks.  Nature at work, unfortunately.

Dave Angelini

Thanks westbranch !  Mostly just ponderosa here so far. The colder elevations above 7,000 feet have been pretty safe so far. 
The one good part of this has been for skilled tree labor.  Pretty soon we will be stealing Canadians to come work in California because no one knows how to work outdoors anymore. I see them sleeping in a ac cooled truck during the day and then they must be dropping trees at night.

Yes nature at work Don.  Glad to have continuity I bet !

mike95490

You need a Lightning Decoy (flagpole or something) to get the strikes away from your cabin & gear

Dave Angelini

It is hard to do that Mike!  Big pines everywhere. Up here in the Sierra with the pines dying it can cost $5,000 and alot more (each)to take them down when they are near a house. They dye so fast that they are unsafe to climb. The expense of heavy equipment is unreal!  I have seen some very cool toys that can just grab the tree and cut in 5 minutes. The operator is in an armored air conditioned cab.

I think Don has done about all you can. You might read his list someday?
 I have a couple clients with similar situations and they store spares in a Faraday cage.

The other nice thing is the DSP on an XW with a gfci controller will shut down in escalating faults and "try" to protect itself. I have a client that went thru an outback inverter every season until he switched.

jonr

> You need a Lightning Decoy (flagpole or something) to get the strikes away from your cabin & gear

But this won't eliminate the huge difference in ground potential between two 325' distant points.  This will want to equalize by traveling on your wires.  So perhaps you need a buried uninsulated ground wire near the tube to give it a better path.  And a few loops in the wires you don't want it to travel on.  Ie, same design as lighting protection for a roof antenna or boat, but horizontal.

mcgivor

Just read the thread and found it to be both interesting and informative. The one thing  Mountain Don said was " FWIW the damage was in an area where the conduit dipped slightly before rising and then falling further down the slope." Got me wondering if perhaps that is where water collected, vaporizing to steam and rupturing the conduit?
There was little  further conversation regarding the lighting strike as the Pine Beetle took center stage, would be interesting to hear some theories on this, seems some have experience with lightning.

Dave Angelini

They are all theories when it comes to Lightning. You can try to reason with it and that often works until it doesn't.
If you like this stuff, search the Telcom industry where they can afford to do Failure Analysis on a professional level.

To me, it gets to the cost point of doing all of the basic things and then just have spares. Doing it right is just not easy, inexpensive, or guarenteed.
Even though we get a few bad ones nearby each year, it is not as bad in this part of the Sierra as some of my clients locations. 

We are up to 102 million dead Pines now in 10 counties with 400,000 trees on the ground. They are starting to fall by themselves now.

cupcake

so wait... all of this happened because you left NM conduit exposed on the ground right?