Author Topic: What is going on here?  (Read 14670 times)

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Offline MikeW

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What is going on here?
« on: August 14, 2015, 09:47:28 pm »
 

Offline jancumps

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Re: What is going on here?
« Reply #1 on: August 14, 2015, 09:49:51 pm »
Blinky for the high power engineer  :)
 

Offline tron9000

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Re: What is going on here?
« Reply #2 on: August 14, 2015, 09:59:48 pm »
tempering the bolt by the looks of it!
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Offline T3sl4co1l

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Re: What is going on here?
« Reply #3 on: August 14, 2015, 10:02:53 pm »
Awww, it's like a pretty jewel... want.... to.... taste....

*ElectroBoom's scream*

Tim
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Offline Chris C

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Re: What is going on here?
« Reply #4 on: August 14, 2015, 10:11:18 pm »
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.)
 

Offline Simon

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Re: What is going on here?
« Reply #5 on: August 14, 2015, 10:16:52 pm »
Oh the warning light came on ;)
 

Offline MikeW

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Re: What is going on here?
« Reply #6 on: August 14, 2015, 10:28:38 pm »
Oh you guys..
 

Offline Deathwish

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Re: What is going on here?
« Reply #7 on: August 14, 2015, 10:54:47 pm »
lick it with your tongue, its a cherry flavoured nut  :popcorn:
Electrons are typically male, always looking for any hole to get into.
trying to strangle someone who talks out of their rectal cavity will fail, they can still breath.
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Offline Pillager

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Re: What is going on here?
« Reply #8 on: August 15, 2015, 01:01:09 am »
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 ;-)
« Last Edit: August 15, 2015, 01:05:26 am by Pillager »
Greets

Tom
 

Offline German_EE

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Re: What is going on here?
« Reply #9 on: August 15, 2015, 07:14:42 am »
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.
Should you find yourself in a chronically leaking boat, energy devoted to changing vessels is likely to be more productive than energy devoted to patching leaks.

Warren Buffett
 

Offline TheElectricChicken

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Re: What is going on here?
« Reply #10 on: August 15, 2015, 09:37:48 am »
Color code : Yellow = cable





 

Offline Simon

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Re: What is going on here?
« Reply #11 on: August 15, 2015, 09:41:10 am »
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.
 

Offline Deathwish

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Re: What is going on here?
« Reply #12 on: August 15, 2015, 09:48:55 am »
You just know that the first pic is of a network in a spaghetti factory dont you ......
Electrons are typically male, always looking for any hole to get into.
trying to strangle someone who talks out of their rectal cavity will fail, they can still breath.
God hates North Wales, he has put my home address on the blacklist of all couriers with instructions to divert all parcels.
 

Offline TheElectricChicken

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Re: What is going on here?
« Reply #13 on: August 15, 2015, 12:02:54 pm »
You just know that the first pic is of a network in a spaghetti factory dont you ......



 

Offline mikerj

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Re: What is going on here?
« Reply #14 on: August 15, 2015, 05:02:08 pm »
That is a nut with a built-in indicator light, to let you know it's not properly installed.

:clap: :clap:  I do like that :D
 

Offline tron9000

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Re: What is going on here?
« Reply #15 on: August 17, 2015, 10:10:05 am »
Or a visible demonstration of Kirchoff's Current Law!
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Offline leblanc

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Re: What is going on here?
« Reply #16 on: August 17, 2015, 04:51:50 pm »
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. 
 

Offline CatalinaWOW

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Re: What is going on here?
« Reply #17 on: August 17, 2015, 06:04:33 pm »
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.
 

Offline electr_peter

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Re: What is going on here?
« Reply #18 on: August 17, 2015, 07:59:37 pm »
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).
 

Offline MarkF

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Re: What is going on here?
« Reply #19 on: August 17, 2015, 10:54:34 pm »
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).
 

Offline SL4P

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Re: What is going on here?
« Reply #20 on: August 18, 2015, 02:35:05 am »
I wonder what gave it away first... the smoke or the smell ?
Don't ask a question if you aren't willing to listen to the answer.
 

Offline CatalinaWOW

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Re: What is going on here?
« Reply #21 on: August 18, 2015, 09:07:07 pm »
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.
 

Offline tron9000

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Re: What is going on here?
« Reply #22 on: August 20, 2015, 07:54:42 am »

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?
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Offline sleemanj

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Re: What is going on here?
« Reply #23 on: August 20, 2015, 09:59:33 am »
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.
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Offline Deathwish

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Re: What is going on here?
« Reply #24 on: August 20, 2015, 10:10:25 am »
i keep watching the nut to the left and waiting for it to fall off...
Electrons are typically male, always looking for any hole to get into.
trying to strangle someone who talks out of their rectal cavity will fail, they can still breath.
God hates North Wales, he has put my home address on the blacklist of all couriers with instructions to divert all parcels.
 


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