Good wire gone bad

[Mike90250]

Been getting high battery voltage alarms from the charge controller, and I went over all the battery interconnects and the terminals in the charge controller with an IR thermometer.

Then, when getting into the ePanel, to prep for the Midnight Controller for the new array, I saw the cause. And all the screws seem tight. Putting in new #4 wire (55A) and buss bar, and that should fix it up. Yow!

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Photos here

[Sunking]

Somebody had a Short Circuit, or a poor connection and never new it. You got lucky it did not catch on fire. If it was from a short circuit you really need to look over your Over Current Protection scheme because something is wrong with it.

Just from looking at it and the location my guess is just a poor termination that heated up. Pretty classic burn pattern for poor connections.

[inetdog]

Wow indeed!

Just from the pictures, I would say that either the screw was not sufficiently torqued down or there were quite a few damaged strands in the wire where it came around the bend.

"Seemed tight" is the operative word here.
Once it has overheated like that, the screw could be binding rather than being fully tight.
I have also heard electricians say that once you have torqued down a screw like that on stranded wire, re-torquing it or removing and replacing the wire justifies cutting back the end of the wire so that you crush some fresh wire.

Also, did you confirm that the terminal is in fact rated for stranded wire in that size? I do not expect that it would not be, but worth a check.

[Sunking]

I have also heard electricians say that once you have torqued down a screw like that on stranded wire, re-torquing it or removing and replacing the wire justifies cutting back the end of the wire so that you crush some fresh wire.

Well on ething every electrician will tell you is all mechanical connections will fail and the stats back that up. In addition a majority of all electrical fires are from poor connections. That is on ereasons utilities do not use mechanical connections. They either use thermal weld or reversible compression.

In addition the Air Craft industry prohibits mechanical electrical connectors. They have to use irreversible compression connectors with calibrated and tested tools.

[inetdog]

They have to use irreversible compression connectors with calibrated and tested tools.

Is that all the way into the powered equipment, or is it also considered OK to crimp a ring terminal to a wire and attach that to a bolt?
I understand that a suitable connector will have very precisely engineered contact force and area, hopefully maintained through thermal cycling, but a bolt and locknut with Belleville washers should be pretty reliable too.
Those high current connector pairs can get really expensive really fast.

[ChrisOlson]

Then, when getting into the ePanel, to prep for the Midnight Controller for the new array, I saw the cause. And all the screws seem tight. Putting in new #4 wire (55A) and buss bar, and that should fix it up. Yow!

Looks identical to wind turbine wiring. Wind turbines can melt anything in sustained high wind.

That screw connection made a pretty nice resistance heater.

[Sunking]

Is that all the way into the powered equipment, or is it also considered OK to crimp a ring terminal to a wire and attach that to a bolt?

That is a irreversible compression.

Here is the tool a DIY would use that cost him $10 at any Auto Parts or Electronic store.



Here is what a Aviation Mechanic or Professional Electrician might use. They are ratcheting and will not let go until you fully complete the crimp. It leaves a Die Mark with either a Letter, Number, Dots, or Symbol so an inspector can verify the correct tool is used. This one tool here made by T&B cost around $250 to $300.



And for wire over #6 AWG up to 750 MCM something like this that uses a hydraulic pump to deliver 15 tons of pressure. .

[Sunking]

Crap they will not let all the pictures go.

DIY



Pro

[Mike90250]

Any short would have tripped a breaker somewhere. The midnight boxes are pretty smart that way. And since that's on the battery buss, a short would be more than spectacular. Till the 250A breaker blows.

#4 into a midnight buss bar, for a 6KW inverter, should have been OK. I'll call midnight and see what the valid range of wire is for the busses. But it sure did work like a heater! And it was coarse wire, not fine welding wire. So that should have been OK. And yep, the heat could have sized the setscrew into the tinned buss, and that's why it feels solid now. And the buss conducted enough heat to melt the insulation on the upper wire too. if it was loose 3 years ago, I'd have been getting the Battery Bus overvoltage warnings for a long time. Just started about 2 months ago. 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 ?

[Shockah]

Brings to mind the old saying "it happens to the best of us".

Glad to see it's ONLY a melted wire and nothing more serious.

[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.

[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?

[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.

[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.

[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.