Good wire gone bad

[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

[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]

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]

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]

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.

[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]

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:

[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.

[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]

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]

Chris I know solar manufactures use mechanical clamps and I hate it. They do so because consumers do not have the tools or knowledge to terminate compression terminals correctly. Mechanical is OK for solid wire but just suks for stranded wire. It is a SORE SPOT with me as you can tell. Reason it is because of just what Mike is going through. It is a very big weakness and a real fire concern. If any of my friends were to suffer a fire from such termination, you can bet I wil be an Expert Witness free of charge to sue the crap out of the manufacture.

[ChrisOlson]

Correct me if I am wrong Mike, but your installation is pretty new isn't it to already have a failure?

I'm not Mike, but it has to be fairly new because MidNite has not had the ePanels out for too many years.

While I agree that that type of bus bar with stranded wire is not the best idea, they do work pretty good if you tin the end of the wire before putting it in the terminal bar. Then retorque it after a few thermal cycles until it gets "seated in". I've only had that type of failure here if I neglected to check the torque on the screw after awhile so it naturally loosens up a bit with time with stranded wire - and you are putting a wire in there that is too small for the hole so it mauls it and gets squeezed out to the side.

The connection on that bar is sort of the same as the connection in a solar MPPT controller. I tried to snap a photo of the connection in a XW-MPPT60-150:



But there is one important difference - the lugs in the solar controller have a set of "jaws" that close on the wire. The screw does not bear on the wire. These ones in the solar controllers don't come loose if they are torqued properly in the first place. When the screw bears on the wire it mauls multi-strand wire from the screw twisting on it as it tightens up. If you tin the wire so it can't get mauled and squeezed out damaging the strands, it will stay tight.

[Mike90250]

Yep 35 years worth. Best grease out there is Sam Chem NO-OX-ID A Special. It is default choice for all utility, bridge, and water works utility. There are installations over 50 years of service with no failures. In electrical applications you apply a very light coat onto wire skinners before compressing terminals on the wire, and a very light coating onto mating surfaces. Even a little bit applied on threads of nuts/bolts to make disassemble easier down the road a few years. Air and water cannot penetrate the stuff.

Mike I must also warn you on the use of flexible power wire designs. Do not use it with any mechanical pressure type connectors like you have in your picture. It is guaranteed to fail. Flexible cable designs are intended to use either irreversible compression connectors or thermal welds. If possible I would advise you to get rid of that term strip in your picture and use a copper buss bar and use compression connectors with two-holes using either 1/4-20 or larger for lager wire gauges above # 6 AWG.

Correct me if I am wrong Mike, but your installation is pretty new isn't it to already have a failure?

That ePanel has about 4 years on it, and that is the high stress (55Amp) wire. I believe Midnight engineered it to work with coarse stranded wire, trying to bend solid wire in that compartment would be quite difficult. I'll be calling them today about this, and posted the pic's at their forum too.

[Sunking]

Anyone have any experience on the copper filled conductive grease ? Is it suitable for set screw terminals ?

Yep 35 years worth. Best grease out there is Sam Chem NO-OX-ID A Special. It is default choice for all utility, bridge, and water works utility. There are installations over 50 years of service with no failures. In electrical applications you apply a very light coat onto wire skinners before compressing terminals on the wire, and a very light coating onto mating surfaces. Even a little bit applied on threads of nuts/bolts to make disassemble easier down the road a few years. Air and water cannot penetrate the stuff.

Mike I must also warn you on the use of flexible power wire designs. Do not use it with any mechanical pressure type connectors like you have in your picture. It is guaranteed to fail. Flexible cable designs are intended to use either irreversible compression connectors or thermal welds. If possible I would advise you to get rid of that term strip in your picture and use a copper buss bar and use compression connectors with two-holes using either 1/4-20 or larger for lager wire gauges above # 6 AWG.

Correct me if I am wrong Mike, but your installation is pretty new isn't it to already have a failure?

[ChrisOlson]

Could have been cold flow loosened the effective torque on the wire and it cascaded from there.

Anyone have any experience on the copper filled conductive grease ? Is it suitable for set screw terminals ?

Mike, the thermal cycles on the wire and bus cause them to get loose after awhile. After 14 years of dealing with wind turbines and having the same problem several times over I have learned that at least once a year go over all the screw lug connections in the system with a screwdriver to insure that they have stayed tight. You will be surprised at how many you can get a "quarter turn" out of after being in service for awhile. Even bolted eyelet connectors on bus bars are not immune. A few years back during a good "blow" I had a wind turbine melt a 1" x 1/2" thick copper bus bar completely off due to a bolted battery cable connection on the bar that had developed a high-resistance connection after being thermal cycled over time.

The screw connections in breakers and bars where the screw pushes on a clamp type deal instead of bearing directly on the wire, I have found, tend to stay tight. The ones where a screw bears on the wire tend to get loose with time. Single strand wire works the best in the connections where the screw bears directly on the wire. Aluminum wire tends to be worse than copper.