All these observations are nuggets of gold, in that it's not intuitive that the grounding system is more branched than the neutral system (which isn't branched); but it makes sense once you point it out.
Then you have to figure out how to connect the second bus to the first one.
What I remember is the set screw looked like it rusted. That suggests that the screw is steel. Steel has a rather different expansion rate than aluminum, and thermal cycling can cause a loose connection. Was the lug rated for aluminum? Expansion rate is one of the problems with aluminum.
What were the instructions for installing the lug? Did the manufacturer want the wire to be wire brushed and antioxide paste used?
Connections for large aluminum wires are generally reliable if the right lugs are used.
Could be it wasn't tightened adequately.
Ah! Now it starts to make more sense! I was trying to figure that out and just couldn't.
I'm amazed at what you can tell just by looking at a panel. I see, well, I see 'stuff' - but you see AA, BB, etc.
Ah. Again, It makes sense! Even though those high-tension wires are insulated, they're carring hundreds of thousands of volts, so, electrons strip off and build up in the metal of the tower (were it to not be grounded).
At some point, that static electricity would be great enough to jump, like lightening, to anything that was grounded.
And, were that to be me, it would be like getting hit by a bolt of lightening.
This is what it looks like:
If it's as simple as a loose connection, once I replace the lug, it's *still* going to be steel on aluminum, right?
If so, the simple answer seems, to me, to be that I should tighten the lugs once a year (or so).
Does that seem viable?
Clarification. You were apparently talking about lightning hitting a tower. I was referring to a downed transmission line. People have occasionally been killed or injured by having one foot closer to the downed line than the other foot.
As in taking a step towards it.
I think the yearly torque and tighten is totally excellent idea. I've gone down the row with screw driver in others power panels, and found loose lugs.
What you see on the lug might be heat related. With heating and cooling of a circuit, sometimes they work their way loose.
Not much of a problem.
It is more familiarity and years of experience. Plus the knowledge of how things are supposed to work. The example you provided was beyond odd.
It is actually the potential voltage in the soil that is a hazard. One foot of linear distance may yield over 100,000 VDC. Humidity and wind play a part in this.
Any new panel I enter gets everything tightened. Period.
With service contracts we would check all connections on an annual basis.
TO lay this one to rest, I snapped a picture of the placard on the generator next to the control panel:
SET EXERCISE TIME INSTRUCTIONS Place Manual/Auto Off switch to "Off" position. Place and hold "Set Exercise Time" switch to "On" postion for 5 seconds. Wait 30 Seconds. Place Manual/Auto/Off switch to the "auto" position. Failure to wait 30 sec. may cause engine to start. If engine does start, it will shut off automatically within 2 min. Generator will now exercise every 7 days, at set time.
It was from the PDF that was recommended earlier in this thread, for me to read, to understand how the power line transmission feed worked.
I turned off the power today, and tightened them all. They were all pretty tight. Only a couple would turn even a fraction of a turn. Specifically, the rusted & burned one was tight.
I turned off the power, and tightened *every* lug on every panel!
Who would have known that's part of normal yearly homeowner maintenance.
The funny thing is that this web site says the aluminum wiring was used in the 70s, but my home was built in the 80s and it has aluminum feeder wires.
Pretty much no one would know.
As to the lug that's rusty, I'd take that screw and wire out, and wire brush the wire and the lug. Might need to go to the plumbing department and buy a 1/2 inch fitting brush. Smaller fitting brush if they sell em.
How would you suggest Danny connect a second neutral bar?
Because of high copper prices, starting about 1965 and going through the early 1970s aluminum was used for 15 and 20 amp branch circuits. There were problems with both the wire and devices (switches, receptacles). There were fires, and as a result there were changes in the UL standards, twice. The link is about 15 and 20 amp branch circuits. The recommendations for making connections that are there somewhere, abrade surface of the wire and apply antioxide paste, are relevant to all aluminum connections.
Aluminum has been used for higher current circuits before that, and is often used now. The connections for 15 and 20 amp branch circuits are much different than for higher current circuits. Aluminum is quite reliable in the heavier circuits, like what you have.
I suspect the failed lug was not rated for aluminum, or was not tightened enough.
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