Good wire gone bad

[ChrisOlson]

Chris I know solar manufactures use mechanical clamps and I hate it.

I think most two-pole circuit breakers rated 30A and above also have those mechanical clamps. They are also used in welders, generators, and quite a few inverters.

[Sunking]

I think most two-pole circuit breakers rated 30A and above also have those mechanical clamps. They are also used in welders, generators, and quite a few inverters.

Is that for AC power?

[ChrisOlson]

Is that for AC power?

Well, some of them. But they are very popular in use on DC welders too that use fine stranded welding wire - both for connecting the wire inside the welder to the bus bars and for the stick holder and ground clamp.

A lot of smaller single pole breakers have a sort of mechanical clamp that consists of a flat plate that is threaded in the center that the screw threads into. As you tighten up the screw it pulls the plate and clamps the wire. Bigger breakers have the same type of "u-shaped" mechanical clamp that the solar controllers use. I've never seen one of those come loose if it's torqued properly.

I've seen lots of connections of the type pictured in Mike's photo come lose with time, especially with aluminum wire. On generators we always used Anderson contact lugs for stranded wire in bus bars of that type on less than 2,000 volts. There's a limit on the number of strands in the wire that you can use in those types of bus bars, but can't remember what it is (like 19?) before you have to use a ferrule or contact lug on the wire.

Edit:
Simply tinning stranded wire also works just as good as a ferrule or contact lug in those screw clamp bus bars.

[ChrisOlson]

I just looked at the MidNite forum and see Mike posted this there too. One of the fellows posted a photo, which I'm just linking to here. On the upper left see where that red wire is clamped in that screw on the bus bar? That's another one that's gonna burn up if it has any real amps going thru it. You can't squeeze your stranded wire out around the screw like that and expect it to stay tight. That's a case of putting too small of a stranded wire in too big of a hole, and then failing to use a ferrule, or tinning it:

[mapmaker]

I just looked at the MidNite forum and see Mike posted this there too.

Look again... that yellow label says to use fine stranded cable. --mapmaker

[ChrisOlson]

Yes, I can see what the label says. But I also know that what is shown in the photo is not the proper way to terminate a stranded wire in a bus bar with a screw like that. It won't stay tight. The process of tightening the screw on the wire grinds on it and squeezes it out to the sides, damaging the strands. So at the point where the wire first meets the screw the wire strands get partially cut thru and instead of terminating a cable with a connection that will handle full amp load, you end up with a fusible link that's going to get hot if you push it to the full ampacity of the wire.

[Sunking]

Edit:
Simply tinning stranded wire also works just as good as a ferrule or contact lug in those screw clamp bus bars.

That effectively makes it a solid wire for which a a mechanical clamp is made for. However it minimizes surface contact.

[ChrisOlson]

That effectively makes it a solid wire for which a a mechanical clamp is made for. However it minimizes surface contact.

Yes indeed. However, those bus bars usually come with several different sized holes. You should insert the tinned wire into the smallest hole it will fit in. The tinning is soft enough so the screw "bites" into it if torqued to the proper spec. But the tinning prevents damage to the strands. And thereby you get the proper amount of contact surface so the connection will handle the full ampacity of the wire. I've had really good luck with using that method.

To each his own. But I maintain that you cannot damage the strands in a stranded wire and expect the connection to handle the full amp rating of the wire. For commercial installations I don't think tinning a stranded wire meets code. They require the use of a ferrule or the Anderson contact lugs we used to use in the generator business on semi-trailer mounted 1.0 - 1.5 MW portables that usually are 480V three-phase and use flexible Type SEOW cable to power off-grid sites like for fairs and circuses, mining sites, etc.. Those low voltage gensets put out 3,000 amps on multiple parallel SEOW cables and the Anderson contact lugs, IIRC, were UL listed up to 2,000 volts and 260A/leg on 4/0 copper cable. I've seen where guys didn't use them and it would melt the wire right off on a straight screw type lug.

But tinning works "good enough" for the poor man doing his own installation, to insure that you don't damage your wire termination when tightening the screw.

[Sunking]

For commercial installations I don't think tinning a stranded wire meets code.

Does not meet residential, commercial, and industrial codes. All are the same. Th eissue is when you tin the wire, you are using it in the manner that does not meet the UL requirements.

The difference between residential and Industrial/commercial comes down to $MONEY$ and quality. You cannot have both. Residential is rock bottom minimum material and quality. Commercial and Industrial cannot tolerate interruptions like a residential application can. A person can certainly use commercial/industrial techniques and design, but it will cost $MONEY$ which most are not willing to undertake, and most are ignorant and do not know there is a much better and safe way.

Not arguing with you Chris, just stating the facts. You get what you pay for.

[ChrisOlson]

Does not meet residential, commercial, and industrial codes. All are the same. Th eissue is when you tin the wire, you are using it in the manner that does not meet the UL requirements.

Yep, I kinda knew that. For somebody working for-hire it better be done right, and that means using the proper ferrules, etc.. But for us off-gridders that live out in the sticks, the chances of the inspector showing up in a black helicopter is probably pretty slim. So I consider tinning stranded wire to be "good enough" to insure that your connection don't give out. When it comes to code, if the inspectors showed up they'd probably condemn our whole place because we don't have the minimum 100A service required for residential

[Mike90250]

Look again... that yellow label says to use fine stranded cable. --mapmaker

I believe that is find strand wire for the massive cable going to the battery & breaker, if it was coarse strand, it would be way too stiff and break a connector, or never tighten properly.

[Sunking]

Yep, I kinda knew that. But for us off-gridders that live out in the sticks, the chances of the inspector showing up in a black helicopter is probably pretty slim.

Trade-Off is the Fireman in Red/Yellow coats and the undertaker Men In Black showing up.

[Mike90250]

So, I'm going to go looking for a crimp on ferrule at any of the stores around here. got to get a pair of them, I'll be adding another controller and another 25 amps to that buss bar.

[ChrisOlson]

So, I'm going to go looking for a crimp on ferrule at any of the stores around here. got to get a pair of them, I'll be adding another controller and another 25 amps to that buss bar.

Mike, was the bus bar and the standoff damaged too?

When we put in our new system I debated and debated over whether or not I should get one of them MidNite boxes. But then decided to build my own. I stole a couple bus bars out of an old Cummins generator switchgear box and mounted them in a grey plastic electrical utility box that I got at Menards. It ain't UL Listed or none of that, but she'll handle 400 amps across the bus bars with no problem and it has bolted connections on the bars with stainless steel bolts. Although I did add a few of them bolt-on screw lugs to connect THHN wire to. I just tinned the wire where it goes in them screw lugs:

[Mike90250]

the hot buss bar crisped the plastic standoffs. Both of them. Got a new wire in today, to a new setscrew in the buss bar, and that's working fine. But #4 wire does heat up with just 45 amps continuous through it, so I may move to #2. Maybe NE code only assumes 30% duty cycle, but with solar PV, when the sun shines, the batteries charge for hours - 100% duty cycle.
And I'll have to recheck the set screws now.
And the large electrical house in the area, does not stock ferrules