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Can the following be caused by short circuit without any arc flash? There was an initial short between lugs and chassis. Did arc flash occur that caused the lugs to melt. Or can it melt just by the huge current during the short circuit?

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In the above. The live wire was lowered by the electrician to the terminal. Then somehow it shorted (between the 208v wire and neutral/chassis ground) causing the breaker lugs to melt and a hole to be produced at the chassis at the back. This also caused a rat size 2nd degree burn in the electrician arm. Was this caused by short circuit without arc flash or was it arc flash?

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    \$\begingroup\$ Both generate heat and cause the plastic to melt. Why do you want to know? This looks more like electrical destruction than electrical engineering. \$\endgroup\$ – Huisman Mar 12 at 9:00
  • \$\begingroup\$ What melted was both metal (aluminum lugs) and plastic. Im studying the electrical enginering of arc flashes. \$\endgroup\$ – Jtl Mar 12 at 9:10
  • \$\begingroup\$ @Huisman I changed the picture to show what melted was not just the plastic but the aluminum lugs. Was it caused by arc flash or just normal bolted short circuit without arc flash. Can over current enough to cause the damage without any corresponding arc flash? \$\endgroup\$ – Jtl Mar 12 at 9:21
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    \$\begingroup\$ You are wasting our time and making it less likely that people can answer well or will try to. You have changed the pictures twice and added text with completely new and different information. My answer was based on the information you gave initially and on your 2nd picture. I did not see your 1st picture as you deleted it. When you ask questions,PLEASE tell us as much as you can initially. \$\endgroup\$ – Russell McMahon Mar 12 at 11:52
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    \$\begingroup\$ I doubt that any part of that is aluminum. Steel probably, maybe brass. Aluminum would be unusual. \$\endgroup\$ – JRE Mar 12 at 11:56
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Most probable casue was a bad contact, it wasn't tighted well. I can see the healthy connection next to it - it's a wrong connection. The wires has to reside in the bottom of the lug, tightening the screw you compress wires and bottom of the lug.

The wire lost contact with the lug, but the distance from lug and wire was so small, that the electric field easily break the air, making an arc. This resulted like everthing is OK, the current was flowing and the appliance worked, but with help of an arc.

This is also one of the causes why houses get on fire.

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  • \$\begingroup\$ But can the small arc formed have enough incident energy to melt the aluminum lugs? \$\endgroup\$ – Jtl Mar 12 at 10:00
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    \$\begingroup\$ @Jtl Yes of course. An arc has a temperature of serveral thousands degrees. In metal forming industries you have arc welder, plasma cutter, arc furnace,... \$\endgroup\$ – Marko Buršič Mar 12 at 10:09
  • \$\begingroup\$ But 208v to neutral was not supposed to form stable arc flash. These are only for 400v. If you short your 120v or phase to phase, can you get melted conductors or lugs like that?? \$\endgroup\$ – Jtl Mar 12 at 10:26
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    \$\begingroup\$ You can find this kind of damage also on low voltage systems like in cars, trucks, boats where the voltage is only 12/24V. \$\endgroup\$ – Marko Buršič Mar 12 at 10:46
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    \$\begingroup\$ Excuse me, but I don't fully understand what you have done. Perhaps you should edit the question with some details on how it happen. \$\endgroup\$ – Marko Buršič Mar 12 at 11:20
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If you see blackening on surfaces above the destruction, it can be caused by long burning, by smoke-soot which lasted many seconds/minutes, without any plasma-explosion.

But if you see blackening on surfaces to the side and/or below, that's caused by "metal-black," pure metal-powder which was condensed out of a blazing bright plasma of arcflash.

Didn't the electrician report a huge flash of light and a loud buzz sound? If they were burned but not electrically shocked, that was from skin contacting the plasma in the arcflash, which is usually far hotter than any flame. (The arc-plasma mostly made of metal-vapor, incandescent gas heated far above the boiling point of molten copper or aluminum.)

In your top picture, the blackening is to the side (so not caused by many minutes of rising smoke,) and it has radial lines from explosive trajectory of gas and metal particles. Almost certainly there was a large plasma (arc flash,) many inches across if not larger. Where it touched cold metal, the vaporized metal inside the flash would condense, forming pure-metal "soot."

Metal nano-powder is typically colored black. Copper, aluminum, even etc., creates a light-absorbing black soot when its particles are fine enough. No carbon needed, the black stuff is pure copper or aluminum. You can buy "platinum black" or "copper black" from chemistry suppliers, which is simply ultra-fine pure metal powder.

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  • \$\begingroup\$ But how could the arc flash happened in 208v to chassis/neutral. The original IEEE 1584-2002 test data set (about 300 tests) included only a SINGLE 208 V result. All the other 208 V results failed because they never got to a stable arc. The original testing used 1/2" arc gaps. The new test data set used to develop IEEE 1584-2018 includes 1/4" gaps and used much thinner "fuse" wires to get stable arcing to occur down to 208 VAC. The obvious consequence here is that it is nearly impossible to have a stable arc at 1/2" (12 mm). What happened in my case is an arc perhaps 1"? I saw it flash too. \$\endgroup\$ – Jtl Mar 12 at 13:31
  • \$\begingroup\$ @Jtl what do they mean "stable?" If your source lacked breakers, and perhaps capable of tens of thousands of watts, and with conductors briefly touched together, then an arc-flash lasting less than 100mS, might be explosively destructive, spraying incandescent metal vapor (arc plasma) and melting the metal surface, leaving black coatings nearby. But it would certainly be completely unstable, and cannot persist after the first "bang!" A paper about stable (continuous, many seconds) arcs does not describe the transient arc-flash created by violent vaporization of the metal contacts. \$\endgroup\$ – wbeaty Apr 9 at 1:03
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That surely looks like a small arc flash to me, and no it does not take a 400V+ line to do it...

The actual voltage dropped across an arc once established can be measured in terms of a few tens of volts, with the rest dropped across the supply impedance (Which is why HUGE currents can flow), given a sufficiently stiff supply a 48V battery bank will absolutely get the job done.

A High impedance connection can of course develop sufficient heat to eventually damage itself, cause an arc and that can then create a path to chassis (Seen that one happen).

A modest arc due to a loose terminal can produce a plasma flame that if it touches earthed metal can go from a few tens of amps to the load via the plasma to a few kA to ground almost instantly (With the corresponding increase in the size of the cloud of metal vapour). TBH it looks to me like that conductor slipped out of the terminal and touched the back panel of the enclosure (You can see bit of what looks like ground zero behind that cardboard box (Get rid of it, cardboard in a distribution cabinet, bad plan!).

From your description that was a electrician failing to isolate the source of supply and feeding the fuckup fairy by working live in a metallic enclosure (Against most countries safety rules), the guy got very lucky.

A really stiff bolted short tends to be unimpressive because the circuit protection will open almost instantly, sometimes get impressive magnetic effects making cables jump, but a hard fault is generally uninteresting.

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  • \$\begingroup\$ What if there was no overcurrent protection or breaker upstream of it and the bolted short circuit continues..how many seconds before the wires and terminals melt and what happens..do they flow down like liquid or vaporize? If so how does the vaporization in pure bolted short without tripping of breaker upstream of it and without arc flash differ to one with arc flash? \$\endgroup\$ – Jtl Mar 13 at 0:18
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Updated: Based on your completely altered question, altered images and new information,
it seems highly likely that arc-flash was the cause of the damage.

Neither the damage to the panel or the damage to the electrician's arm is likely to occur without an arc being present.

A POSSIBLE mechanism is that the short circuit current overheated a poorly made connection at the breaker which released the wire. The wire then swung into contact with the panel with the results seen. Damage to breaker probably due to initial failure and subsequent arc due to swinging lead.

Most very major catastrophes require 4+ unexpected or impossible things going wrong 'simultaneously'. In an entry level catastrophe like this it may only have taken two.
- Firstly the poor termination of the wire.
- Secondly the wire then swinging against the panel.


Older: The fact that the adjoining connector shows no damage strongly suggests that it was not involved in the incident.

You can get damage that looks much the same as this without arc-flash.
As Marko says, a poor connection can cause this sort of damage.
Resistive heating increases with the square of the current (Power = i^2 x R). A short circuit current say 10 x normal operating current will result in 100 times as much power dissipation across any resistive components. If the connector was not properly used it would be easy to get enough heating to destroy it.

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  • \$\begingroup\$ It occured suddenly bec live wire was being lowered down for first time to the unused breakers. It shorted. Can bolted short cause that without involvement of arc flash? \$\endgroup\$ – Jtl Mar 12 at 11:20
  • \$\begingroup\$ @Jtl As above - yes. A high current and a poor connection may cause heating 100+ times higher than usual. \$\endgroup\$ – Russell McMahon Mar 12 at 11:32
  • \$\begingroup\$ But can it cause the melting slag to be blown to the surrounding area that can cause rat size 2nd degree burn in the electrician arm? Can normal short circuit without arc flash do it? Or was it arc flash? \$\endgroup\$ – Jtl Mar 12 at 11:46
  • \$\begingroup\$ Sorry. I didn't include the panel picture or hands injury detail because I was hoping to hear that resistive heating can melt the lugs and it can spread the debris to the surrounding (without getting into complicated details that may not be appropriate for question and answer format here). But if the current would be very high. Couldn't this vaporization of the melting lugs occurred without any arc flash? \$\endgroup\$ – Jtl Mar 12 at 12:34
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    \$\begingroup\$ @Jtl "vaporization of melting lugs," that's called arc flash. Vaporized metal is intensely bright, incandescently hot, a jet of arc-plasma. If there was no bright flash of light, then there was no vaporized metal. (But the radial-pattern of blackening is the signature of arcflash plasma, it's the place where the arcflash incandescent metal-vapor condensed instantly on a cold surface) \$\endgroup\$ – wbeaty Mar 12 at 13:25

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