AC input issues with solar power system

[Subdood]

Hey all, I had an incident occur with my solar setup and thought I'd share my experience.

A couple weeks ago, I had my EG4 6500EX on grid bypass power and grid charge because we had had several days of cloudy weather so the batteries weren't getting hardly any charge at all. In the afternoon, the batts were about 75% charged and the system was still in bypass mode (SUB mode, no solar available, so basically grid power). I noticed that the lights started flickering and I thought that I was hearing the relays clicking on the inverter.

I went to the solar closet and saw on the inverter display that the grid icon was blinking on and off, and the AC input voltage was around 50V, nowhere close to 120V. The clicking was the bypass relay switching and the system switching to battery mode.

At the time we were going thru a family emergency, so I was already distracted. I figured we were going to have to leave the next day so I had to figure it out before we left. I didn't want to leave the system going like this if we weren't going to be here for a while. I tried a few experiments that bore no fruit that evening so I decided to put the system in battery mode and deal with it the next morning. The only relevant thing that I noticed was that with the grid power breaker turned off at the pole panel, was that there was no continuity between the neutral and ground wires. There should've been because both wires are bonded at the panel.

We had to leave the next morning, so I decided to turn off the entire system, and put the shed and refrigerator circuits back on the grid while we were gone. The shed has a freezer in it, so obviously I needed those two circuits on grid.

Fast forward a week, we returned home and I was wondering what could've went wrong. The fact I couldn't get continuity between the N and ground wires at the inverter kept sticking in my mind. Yesterday after we got home from work, I returned the pole panel where the wires were hooked up. The neutral wire is 4awg, so it was too thick to fit into the holes on the ground bar. When I originally did the wiring here, I used a jack that screws into the bar and the larger wire and was tightened with another screw.

The screw has an odd star head which required a special bit to loosen which I just found I had yesterday. So after loosening it, I took out the wire and saw that the copper was very oxidized with green and white gunk on the wires. This was the culprit. There was so much oxidation it was keep it wire from making a good contact with the jack and thus, the ground bar. See attached pics for the evidence.

So I cut off the bad wire, restripped it, scoured out the jack as best I could and reinserted and tightened the wire. I didn't get it perfectly clean, but it was good enough for a solid connection. I hooked up a jumper wire between the neutral and ground wires there and went inside to measure the continuity and there was zero ohms, perfect. So I hooked the two wires onto the ground bar and did a few tests before I powered everything back up. Before powering up the inverter I checked the AC voltage at the inverter and it read 120V.

Everything looked fine so I powered up the inverter in bypass (grid) mode and checked a few circuits on the critical loads panel to make sure it would take a load, something it wouldn't do before. Those turned out fine, so I felt confident enough to turn all the circuits with no issues. I switched the inverter over to battery mode and it worked fine and has been running good.

SO, to end this novel, the issue was a wonky neutral connection at the pole. I'll be picking up a new jack and get some anti-oxidation goop to put on the wire to prevent this from happening again. Thanks to @Steve777 for troubleshooting suggestions.

 

[WorldwideDave]

Wow lots of oxidization.

 

[Subdood]

Could I use Noalox on the copper wire where it goes into the lug? I'm assuming the lug can accept either aluminum or copper, so I don't think it's a galvanic corrosion issue?

Or should I use dielectric grease?

 

[Subdood]

Here's a pic similar to the lug I used. Small screw attaches lug to neutral/ground bar, large screw secures wire to lug. I'm using 4 AWG copper.

 

[MattMan119]

I would suspect that you have high moisture in the area with these connection.. I would definitely give them some noalox or dielectric grease that would limit it.. depending on the amount of moisture I would recheck from time to time…

 

[Q-Dog]

I'm assuming the lug can accept either aluminum or copper,

It should have CU/AL printed on the lug if it is copper and aluminum compatible.

 

[Subdood]

I would suspect that you have high moisture in the area with these connection.. I would definitely give them some noalox or dielectric grease that would limit it.. depending on the amount of moisture I would recheck from time to time…

Well it's at the outside pole panel, so it gets plenty of humidity. It is inside a weather proof panel box, of course, but that's not going to keep the humidity out.

Does it matter if it's Noalox or dielectric grease, or are those the same basically? This connection is for grid backup to the inverter, but we rarely use grid unless the batteries are low and they need to be charged via the grid and/or we need grid to run the 120V loads. 240V loads are still on the grid.

 

[Q-Dog]

Does it matter if it's Noalox or dielectric grease,

Use whichever you have. I use dielectric grease a lot on automotive applications, so I have plenty of that.

 

[Hedges]

Yes, goop the connection.

Terminal is tin plated aluminum, not meant to get wet. But used in outdoor 3R boxes, needs to be humidity tolerant.

Tiny flat-head screw is all that connects lug to aluminum busbar. I've got one like that coming out of utility/meter side of a 200A box. Don't like the idea of losing neutral and getting 240V split unevenly between loads on the two legs

Since that goes onto a neutral/ground bar, is there another screw location that could secure a different lug better?

 

[Subdood]

Yes, goop the connection.

Terminal is tin plated aluminum, not meant to get wet. But used in outdoor 3R boxes, needs to be humidity tolerant.

Tiny flat-head screw is all that connects lug to aluminum busbar. I've got one like that coming out of utility/meter side of a 200A box. Don't like the idea of losing neutral and getting 240V split unevenly between loads on the two legs

Since that goes onto a neutral/ground bar, is there another screw location that could secure a different lug better?

Yeah there's a few other locations on the bar I could use, but space is limited. I think I screwed the lug into a different hole on the N/G bar.

Thankfully this is just for a 120V connection, so I don't have to worry about unbalanced legs.

I'm going to pick up a different lug today. I scoured off the original lug best I could but I just need to get another one along with some goop of some type.

 

[Vigo]

There are probably multiple connections in the same ambient conditions there and probably only one of them got seriously corroded, right?

It was probably never a 'good' connection to begin with. Poor connection = resistance. When you flow current across resistance, you drop volts. But they don't 'go away', it's an energy conversion. In this case it converts to heat. Wire corrosion = oxidation, which is a chemical reaction that accelerates with heat.

So, a poor connection gets hot and corrodes faster than the other connections right next to it.

Grease would slow or stop the oxidation, but it wouldn't address the connection having high resistance in the first place. If a wire gets hot enough, the grease will mostly run off of it anyway. So grease is 'nice' but it wouldn't have fixed the original issue here.


Another thing about a bad connection on a neutral is that depending on how balanced the loads on each 'leg' are, a bad connection to neutral will cause a voltage shift between legs. Whichever leg has more resistance in the circuit will drop more volts, and the leg with less resistance will drop less volts. So a bad connection to neutral could cause one leg to go up to 180v and the other one down to 60v, etc.

 

[Hedges]

Yeah there's a few other locations on the bar I could use, but space is limited. I think I screwed the lug into a different hole on the N/G bar.

Thankfully this is just for a 120V connection, so I don't have to worry about unbalanced legs.

I'm going to pick up a different lug today. I scoured off the original lug best I could but I just need to get another one along with some goop of some type.

Ignoring whatever the NEC might say, I'd much rather split the strands into two groups and slip into two adjacent N/G bar holes. Set screw compresses it against surface, doesn't have separate joint.

At least that lug has an extension to keep it from rotating on bar.

I find I can it up to 4 awg in ground bar.

Downside of my idea is you can't rotate the two groups of strands to promote settling while re-torquing.

 

[Subdood]

Ignoring whatever the NEC might say, I'd much rather split the strands into two groups and slip into two adjacent N/G bar holes. Set screw compresses it against surface, doesn't have separate joint.

At least that lug has an extension to keep it from rotating on bar.

I find I can it up to 4 awg in ground bar.

Downside of my idea is you can't rotate the two groups of strands to promote settling while re-torquing.

I think largest wire I can get in my ground bar holes is maybe 6, or 8, so 4 is a no go. To be honest, it'd be a pain to try to strip out the 4, and then separate them into separate smaller strands.

 

[Subdood]

There are probably multiple connections in the same ambient conditions there and probably only one of them got seriously corroded, right?

It was probably never a 'good' connection to begin with. Poor connection = resistance. When you flow current across resistance, you drop volts. But they don't 'go away', it's an energy conversion. In this case it converts to heat. Wire corrosion = oxidation, which is a chemical reaction that accelerates with heat.

So, a poor connection gets hot and corrodes faster than the other connections right next to it.

Grease would slow or stop the oxidation, but it wouldn't address the connection having high resistance in the first place. If a wire gets hot enough, the grease will mostly run off of it anyway. So grease is 'nice' but it wouldn't have fixed the original issue here.


Another thing about a bad connection on a neutral is that depending on how balanced the loads on each 'leg' are, a bad connection to neutral will cause a voltage shift between legs. Whichever leg has more resistance in the circuit will drop more volts, and the leg with less resistance will drop less volts. So a bad connection to neutral could cause one leg to go up to 180v and the other one down to 60v, etc.

I tightened pretty tight I had thought (this was about two years ago), so maybe it came loose a bit. But the screw was on there pretty good when I took it out.

 

[Hedges]

Wires settle under the screw. This isn't like a gas-tight crimp connection that mashes the hell out of it.
Standard advice is re-torque 24 hours later.

My advice is bend the wire into an "L", then wiggle back and forth causing strands to rotate under setscrew. Keep snugging and rotating until screw won't turn any more.

Corrosion inhibitor is a good idea. Equipment often comes with a little bit pre-applied.
I undid a bunch of wires to QO 3R safety switches, but one I couldn't turn the screw, and to cut wire. The threads don't appear to have corrosion inhibitor. Maybe I over-torqued and damaged tin plating.
And that was in a mild location, not coastal or anything like that.
I'd rather not have aluminum, but it is used all over my favorite equipment.

 

[Subdood]

Wires settle under the screw. This isn't like a gas-tight crimp connection that mashes the hell out of it.
Standard advice is re-torque 24 hours later.

My advice is bend the wire into an "L", then wiggle back and forth causing strands to rotate under setscrew. Keep snugging and rotating until screw won't turn any more.

Corrosion inhibitor is a good idea. Equipment often comes with a little bit pre-applied.
I undid a bunch of wires to QO 3R safety switches, but one I couldn't turn the screw, and to cut wire. The threads don't appear to have corrosion inhibitor. Maybe I over-torqued and damaged tin plating.
And that was in a mild location, not coastal or anything like that.
I'd rather not have aluminum, but it is used all over my favorite equipment.

I don't know what the torque specs are, tho. I just tighten until it's pretty snug, but I always worry about going gorilla and breaking something.

We aren't in a coastal area, but it is pretty humid, even in the summer. I lived in North Texas for 30 years, and I could tolerate the heat more there than here. Or maybe it's because I'm older.

 

[Steve777]

Might be good to put some of the goop under the terminal, between it and the neutral bar. As well as on the wire that goes into it. It's sorta like chicken soup, can't hurt

 

[Subdood]

Yep, can't hurt. I went to Lowe's after work and got a new lug and some no-ox goop. Will try to get it swapped out tomorrow if possible. I do have this grid feed breaker turned off so there's no rush. I usually run the system off solar/battery anyways.

We've had a couple days of good sun, including today. From 8:30a to 5:30p it was >300VDC, what I consider operating voltage.

 

[Hedges]

I don't know what the torque specs are, tho. I just tighten until it's pretty snug, but I always worry about going gorilla and breaking something.

Trouble is they settle. Might be torqued today, but in the future they are loose.

That's why I say wiggle in a manner that causes strands to rotate back and forth in the lug, snugging the screw repeatedly until it stops turning.

I do use a torque wrench for larger lugs, which take about 20 ft.-lbs.
I need to get a torque screwdriver for smaller ones.

You can probably get specs from any other brand with same thread size. My Square-D panels have a couple specs on their label.

We aren't in a coastal area, but it is pretty humid, even in the summer. I lived in North Texas for 30 years, and I could tolerate the heat more there than here. Or maybe it's because I'm older.

Goop, like everybody is saying.
I got some grease with copper shavings. Plenty of choices.
I've seen instructions to splay strands apart and fill between.

 

[Subdood]

Yesterday I installed the new lug with copious amounts of no-ox goop. Also put some on the hot wire where it goes into the breaker. Interestingly, that wire had hardly any oxidation on it, compared to the neutral wire. Why is that?

Anyways, got everything tightened back up and turned the grid back on. No issues. But, I eventually shut it off as it's been sunny and the solar/batteries can handle the loads.