A bit of a problem.
Yesterday when we finished our second 350’ 7 wire pull we discovered that one conductor had slipped out of the pulling head and didn’t make it to the other end.
Ugg.
This is a real problem. We used a machine to pull these wires in( that’s the tugger), but the machine isn’t capable of pulling these wires wires out without damaging the wires.
Sometimes you can use one remaining conductor to pull in the missing conductor and it’s replacement-but the longer the conduit run, the more likely that fails or becomes very difficult due to how the wires twist around each other in the conduit. And this was a pretty long run. And often enough, the conductor you used as a pull wire becomes trash. Not a pleasant prospect given how long this wire is and how expensive it is.
In our case, the problem was further compounded by the type of wire we used-PV wire.
PV wire has an extra thick insulation designed to resist UV Rays and normally you don’t pull it through conduit because that thick insulation takes up a lot of space and is also very “sticky” and so doesn’t pull through conduit worth a damn.
We normally wouldn’t put this stuff in conduit for all of these reasons. However, the high voltage of these strings exceeds the 600 volt rating of normal THHN/THHW wire. This PV wire has a rating up to 2000 volts and as expensive as it is, was the most cost effective solution for the high voltage solar circuits.
So that leaves us with a difficult decision-use one wire to pull in two new ones, or pull out the entire 7 wire bundle and then pull them back in Either option has a real risk of failure and we could end up having to scrap all 2,450 feet of wire.
We elected to pull the entire bundle at once, as it had the best chance of success in our opinion. However, that brought up another problem. We had to use copious amounts of wire, pulling lube in order to overcome the friction that comes with this PV wire. That means the wire would be coming out coated in lube, and if we laid it on the ground, every little pebble, stick, and piece of debris would stick to it, and you cannot put the wire back in the conduit that Dirty or it will damage the wire.
So we came up with the idea you see in the picture above we carefully spooled it back onto a half full wire reel.
Thankfully, all that lube made it possible to pull the entire bundle back out of the conduit by hand, which was a real concern if we would even be able to do that. It was doable, however, I got one hell of a arm, elbow and shoulder workout out of the deal!😬😬
Anyway, after about a 2 1/2 hour delay due to our little mishap, we finally had all the wires pulled into the gutters out at the array pad and into the disconnects there. Just before sundown, we had all of the make up done in the disconnects and were ready to close up these gutter covers and disconnects for the final time.
Even in the fading light of the early evening, each one of these solar circuits had a voltage of well over 700 V. That is nothing to mess around with, and we took no chances and tagged out the disconnect so that somehow they didn’t inadvertently get turned on while we are still terminating the other end of them.
Normally, I don’t do electrical connections in this order. As sort of a double back up, I usually do connections from the “dead” end of the wiring and hook them to the power source last. This creates sort of a second layer of protection against accidental electrocution. However, in this case because we are pressed for time, it made more sense to terminate the disconnect or “live “end of the wiring first.
As the sun made its daily drop below the western mountains, we were finally moving the freight shaker off of the array pad and back over to the equipment pad. Our time crunch and the lost time with the wiring mishap and some other problems we encountered throughout the day meant that we would be working late into the night to try and stay on our tight time schedule.
By around 9 PM that evening, we had all of our DC power conductors and our communication cables pulled into the batteries and had made significant progress elsewhere. By then we were tired , cold, and it was time to hit the rack for some rest and tackle all this again in the morning!