What is going on here?

[MikeW]

[jancumps]

Blinky for the high power engineer 

[tron9000]

tempering the bolt by the looks of it!

[T3sl4co1l]

Awww, it's like a pretty jewel... want.... to.... taste....

*ElectroBoom's scream*

Tim

[Chris C]

That is a nut with a built-in indicator light, to let you know it's not properly installed.  Tighten it by hand.

(It may have really been a bit loose at one point.  Or surfaces in the junction had a bit of surface oxidation.  Either way, the junction had enough resistance to make it heat up under heavy current, which causes it to oxidize more, and so on until failure.)

[Simon]

Oh the warning light came on

[MikeW]

Oh you guys..

[Deathwish]

lick it with your tongue, its a cherry flavoured nut 

[Pillager]

A blacksmith would say it's very heavy (because nothing's too hot, they drop it because it's heavy ;-)

Let's look at this logically.

Why would the nut get so hot (unless someone used a torch)?

Because of a large-ish amount of power gets converted to heat.

That shouldn't happen on a connection. What causes power loss in casas like these?

Resistance. When does a connection have a higher resistance than normal?

Loose nut, corrosion, or both.

I asume the "wire" (and a cute little thing it is, too) is intact and not broken or damaged at the connection point (at or inside the lug)?

If you want to repair this, shut off the system, and wait 10 - 20 minutes for it to cool (and yes, I forgot that once ;-)

Then unfasten the nut and remove the lug. Give the lug, copper bar and screw a good scrub with a brass brush and check for any damage.

Put some fresh shrink tubing over the lug, leave enough clearance around the hole to ensure a good solid connection between the lug and the copper bar. This might have been the original problem.

Get a new nut and, if all else checks out, connect it again. Make sure to tighten the nut properly, but not too tight, or you will destroy the screw.

Check to ensure no tubing is between the lug and the bar, and try wiggling the "wire". If satisfied with the connection, power it up.

We nearly had a forklift battery explode because of something similar, so I wouldn't wait too long.

Or, if you don't feel up to the job (which isn't uncommon in scary high power systems), tell someone who is responsible for the system, before you get hurt or start a barbecue ;-)

[German_EE]

Looking at the right side of the strip it looks like there's a lot of heat so they could start by redistributing the connections better across the busbar. A small amount of conductive grease (I believe it contains copper) will help here as well after everything has been cleaned up.

Nice picture though.

[TheElectricChicken]

Color code : Yellow = cable

[Simon]

wow, in military looms everything tends to be white just because the wire is not cheap and comes with a minimum purchase of 1Km but wow with all that wire surely they could change some colours. Or maybe it would just look nuts.

[Deathwish]

You just know that the first pic is of a network in a spaghetti factory dont you ......

[TheElectricChicken]

You just know that the first pic is of a network in a spaghetti factory dont you ......

[mikerj]

That is a nut with a built-in indicator light, to let you know it's not properly installed.

  I do like that

[tron9000]

Or a visible demonstration of Kirchoff's Current Law!

[leblanc]

I've had this happen to me too. The bolts/nuts need to be very tight, make sure the holes are just big enough for the bolts, and that washers ensure maximum contact surface.

If the contact is not quite good enough, the metal heats up, oxidation takes place at a super-accelerated rate (in a matter of seconds), this makes the resistance much higher (can easily make it in the order of kohms), then even more heat is dissipated here (P=R*I^2).

How to fix it? If possible, replace busbar. The contact area should be bare copper, so file down the area around the holes. Get new screws with the proper material and coating (I don't know too much about this one). Replace ring terminals, ensure that there is no oxidation on the surface. Make sure the bolts are tightened thoroughly. 

[CatalinaWOW]

The more interesting question is why the nut and visible part of the bolt is cherry red while the washer and lug show no visible signs of heating, meaning they are probably a couple of hundred degrees cooler.

My guess would be that there is poor electrical, but relatively good thermal contact between the lug and the brass bar.  Good electrical and thermal contact between lug and washer.  Thus the primary electrical flow is from the lug, through the washer to the nut, then to the bolt and back to the brass bar.  Maybe the electrical contact between nut and washer is also good.  Then the heating would occur at the nut-bolt interface.  The cooler temperature of the washer would be explained by the better heat sinking to the lug (larger area and possibly lower thermal resistance on the lug side), and the lower temperature of the lug by larger area of contact with the brass block.

So root cause is tarnish on the brass block and lug.  Perhaps it wasn't cleaned at last installation, or wasn't tight enough to form a gas tight seal.

[electr_peter]

My guess is that everything is badly oxidised (bus bar, lug, washer, nut) and that nut has a sharp/pointy and non-oxidised corner. That corner somehow scraped a washer and got a good electrical connection while all other nut-washer interface is oxidised and very resistive.

Now, with such high currents flowing though, single point on a nut cannot do full job of nut, thus heating till red glow. Oxides are pretty good thermal isolators, so high local heating is possible.

I think that the root cause of all these problems is an over-current and not a simple loose nut. Connections were pushed over limit, metals overheated (slightly), the got rusty. From this point on, thermal runaway is going to be worse and worse.
Only possible solution - replace everything with shiny new cables and connections (and higher rating for a good measure).

[MarkF]

We always used conductive sliver paste on those connections too.  Most of our bus bars were 1/2" thick anodized bars with threaded holes (no nuts).

[SL4P]

I wonder what gave it away first... the smoke or the smell ?

[CatalinaWOW]

This picture poses so many questions.  How many of you would stop to take the picture upon discovering this?  How many bad practices can you spot in this one picture?  How long did this situation carry on before discovery?  (Based on the oxidation on the stud it was probably quite a while).

Thanks for posting.  The photo has entertained me on many levels.

[tron9000]

to me that looks like neutral is connected to that whole bus bar! erm....ok!

insulating tape round the crimp lugs - why? what are you hiding?

[sleemanj]

Contact resistance heating always makes me think of Goldilocks.

If the resistance is very low, no heating.
If the resistance is very high, no heating (and no current).
If the resistance is juuuuuuussst right, burn your house down.

[Deathwish]

i keep watching the nut to the left and waiting for it to fall off...

[Gyro]

Don't know if it's my imagination, but there looks to be less visible thread length above the nut and the tab doesn't look to be flush with the buss bar (hard to see). I don't suppose it's possible that someone put a washer underneath it?     Maybe it's just a thicker tab compared to the one on the right.

[AF6LJ]

I have two words for you......

  Ohms Law

[/b]

[jlmoon]

That red nut is a "POWER ON" indicator.   

[Kintekobo]

What I find puzzling about this picture is why is just the nut glowing cherry red when there should be little or no current actually flowing through the nut since it is above the current path. The current should be flowing through the cable to the terminal and then to the bus bar. For the nut to be that hot would suggest that there is no or poor current path between the terminal and the bus bar and all of the current is travelling up, through the nut and into the bolt and then to the bus bar.

[AF6LJ]

There is a gob and a bunch of If's and What-if's implied in the picture.

The picture does have a certain "coolness factor" going on with it.

[jlmoon]

What I find puzzling about this picture is why is just the nut glowing cherry red when there should be little or no current actually flowing through the nut since it is above the current path. The current should be flowing through the cable to the terminal and then to the bus bar. For the nut to be that hot would suggest that there is no or poor current path between the terminal and the bus bar and all of the current is travelling up, through the nut and into the bolt and then to the bus bar.

I am venturing to guess on this one:  Yes the nut is above the path for current... but is it really?  Especially if the joining surfaces between lug and bus bar are high in resistance due to state changes in conductive surfaces.  The Nut could be "Dicks last resort" for a current path that is from top surface of lug through washer into nut and back to bus bar via threads of stud.  Possible?.. Yes!!!

and I read back a few post and Catiline..... had the same exact explanation. 

[jlmoon]

I have two words for you......

  Ohms Law

[/b]

Is it my tendency of overkill or shouldn't the conducting surface area be close to or equal to the cross sectional area of that current carrying conductor?  Not sure but think the stud, lug, washers & nuts could be a size or two larger. 

[Kintekobo]

jlmoon[size=78%], I would agree with you there. That is one hell of a thick cable but it ends in a fairly insubstantial lug. Unless of course the cable is thinner than it appears and is covered with a very thick insulation making it look thicker than it is. Somehow I think it is the former rather than the latter judging by the heat [/size]generated.

[AF6LJ]

I have two words for you......

  Ohms Law

[/b]

Is it my tendency of overkill or shouldn't the conducting surface area be close to or equal to the cross sectional area of that current carrying conductor?  Not sure but think the stud, lug, washers & nuts could be a size or two larger.

That picture leaves a lot to question, under good conditions those nuts and studs look large enough. At the same time both of the large wires show heat damage, it could be from the one bad joint, or not.

Actually this picture is a prime example of why a picture is worth a 1,000 words.
So much speculation.

[Gyro]

The more you look at that photo, the more you see...

From all the blue wires I assume it's a Neutral Bussbar (those live brown wires at the right look a bit close considering how hot it must have been).

Curiously the wire that is snipped off on the first visible tag on the left had BROWN insulation 

[tron9000]

The more you look at that photo, the more you see...

From all the blue wires I assume it's a Neutral Bussbar (those live brown wires at the right look a bit close considering how hot it must have been).

Curiously the wire that is snipped off on the first visible tag on the left had BROWN insulation 

Dear god! yeh! what the hell is this butchery?!