Wallwart safety hazard you'd never consider.

 Well it seems like several people have now come to the conclusion that the chain was in direct contact with the prongs.     If you look closely at the prong itself you see that a semi circular piece is missing! How is that possible if the prongs were fully engaged into the receptacle?

 What you saw and what actually happened maybe two different things. I have worked with many a technician who claim they saw this or that but in the end it was determined that their observations were completely wrong.

The only way  you can validate your initial post with respect to the Shorting  is to reconstruct the same scenario and see if it happens again. That's the scientific method that used in industry to to validate equipment malfunctions.

 It may very well be that you have a defective device but it cannot be ruled that all such devices have the same shortcomings especially since others have not been able to duplicate that scenario.

Look at the base of the prongs,  there is a distinct burned out weld mark notch on the base of each prong  which seems to perfectly match the size and shape of the individual balls on the chain. 

I admit I am using a large flat screen TV to view this but any close attention in person would reveal  this.

No need to chase down a rabbit hole for other reasons.

EDIT:  I just shunted over to my laptop screen.  The twin burn marks and dips are there but not as apparent as a large flat screen would show.

Die cut.

Adriatic posted:

  The chain's link between spheres seems like the weak point in the high volt short theory to me too. I'd think that link would be lucky to pass 2 amps without distructive heat. I pulled on the chain to check for softening; but over hardening is still a possibily.

This clearly flies in the face of what you've said recently, and it's also totally incorrect. 

You maintain that somehow, the even smaller conductor in the output line was able to inductively couple enough energy to do all the damage, yet you discount the possibility that the bead chain could cause the damage directly across the prongs of the outlet!  Let's dispense with that misconception right now.

I dug a hunk of bead chain out of my junk drawer.  The beads are 2.5mm (1/10") in diameter, i.e. a fairly light bead chain.  I connected a Z750 transformer across the chain and increased the current until the breaker tripped.  I got a trip after about 5 seconds of over 6 amps.  The bead chain was undamaged and totally unmarked, I see absolutely no difference in the chain from before the tests.

Here's the pictures.

Transformer connection to section of bead chain

Current flow through bead chain

Bead chain after testing, note that it is unmarked

Clearly, the bead chain is more than capable of carrying that much current and more!  Before you jump on the fact that I was using low voltage for my test, we'll head that argument off as well.  It's current that would do the damage to the chain, it doesn't matter what the applied voltage is, basic Ohm's Law.  The only thing the higher voltage did was make a more spectacular arc when the chain contacted the prongs.  I'm about 99.9% certain that this chain shorted directly across the 115V 15A circuit would easily trip the breaker with no significant damage to the chain, I'll leave that to someone else to verify.

Hey John. I have been following this post more for amusement than anything else. I am a structural draftsman, have been for over 45 years.

If I have learned anything throughout my work life is......never argue with an ENGINEER! 

Even the SPARKIES

You have been making perfect sense with your explanations and intuitive comments.

Just my two cents!

Donald

I again post my confidence in the "bead chain shorting across the AC plug" explanation.

I have never seen a plug that had die cut notches at the base of the prongs...

A direct short across the low voltage wire,  if the high voltage side was getting through, would have melted the wire a lot! and there would not be a burn mark across the white outlet.

There is no reason for the black trace marks across the white outlet except for the fact that the bead chain made them...

Just as an FYI:

When 3 prong AC outlets are installed in a home, some electricians mount the ground prong UP (more so in commercial installations), even though most people do not mount them that way.  One reason?  If a plug is in the outlet loosely, then a falling metal object that wedges its way between the plug and outlet would likely hit the ground prong instead of shorting out the plug/outlet.  No, it's not in the NEC, but it does make sense...

Kinda like GRJ's early explanation of the situation.... it does make sense!

 NOTICE: There will be a meeting of the Wallwart Shorting Society in the Orange Hall at York on Friday....time and location to be determined!

Ok that narrow link can carry far more than I thought. I guestimated from fuse wire dia. without considering metallurgys.

  With "huge" prong damage being an visually observed factor by some (the notches were just under bead dia. and larger than link dia.).  Why is the chain undamaged other than anodizing.? Why did two breakers not pop?

For the latter, with or without chain shorts or backfeed; simple, enough amps were not drawn for an overload. But it is odd that it didn't trip either if all that carbon came from a direct short and not a feedback loop.

I see three pieces of workable fact. The prongs are the strong point for me getting enough shock to effect my vision, but not feel .

Chain: light streaking carbon, anodizing lift, no pitting damage. 

Prongs: heavy carbon, small metal flower where only a link can fit*.

Sparks seen along low volt & carbon streaking (hearsay)

* if the link got over the prong till it contacted the I.Dia of the notch, it would likely have snagged as I withdrew the chain, the snag would have been as equally likely to have been noticed, more so because I was kind of expecting it to be a short on the plug myself. 

  I get what the heavy carbon looks like; it's presence was unexpected because that isn't where I saw sparks. I considered reflections, but there was carbon streaking along the top side of the rubber not just the bottom.

  Just for fun, could the repeatetive spherical shape of the chain effect the power fields running along it? Would it be more suceptible to cross wire induction wtih a wire partially in the valley between those sheres? I think so, a  wires crosssection vs expected fields is how they decide on insulatiion. Is it relevant in induction? No clue.

And landing centered between the the two topic stances; If there was a single prong chain connection, can that single leg be drawn on if induced by another current containing the other leg, or is there backfeed protection I'm just not considering. How about off phase possabilities& cancelations? 

  I still have chromed and stainless wall socket covers. My sockets don't get broken by anything other than cord abuse and I attribute that to the covers low profile and taking abuse  well.

   I tighten loose sockets, but had a border let one go totally until the plate did fall and short. He has tempered glass or ceramic covers now, and eyes watching him closer.

Hello 3 Rail 2,  You are correct in your assessment that you shouldn't argue with an ENGINEER especially if they if they have test lab experience!  This is because they've seen every trick in the book that technicians try to use to get out of work or to cover up their mistakes!  

Once you let the magic smoke out, there's no covering it up!

Kazar , The engineer was not here, and things slip by engineers too. I'm not discounting or putting them on a pedistal. I am listening, Ive heard the explanations on the plug, but nothing on the other carbon traces on the low volt.

I have had to chase non destructive feedback loops as a distict technical manager, worked with high voltage and low voltage near daily, and spoke with design engineers regularly. I'm familar with scientific processing and Ive set up a few things in the rooms of a million gadgets beating things to death too. Ive seen some big rooms that would entertain you all day. The lab can't find every issue, the real world usage and hands on repair folk do that later.

 I have not seen wall warts do this before that I recall, but have seen this in larger power supplies. And some that even ended up with toasted plugs just like this, but kept working; not once, not twice, but a handful of times.

Those had locking covers on them, no chain to blame.

  I've seen games and machines in the dark, on, working, and throwing enough blue spark around in the cabinet to look like an old car engine on a wet night...but still working. High volt low anp static traces from induction & dust. I have other induction hunts in communications and high voltage but had an engineer handy to explain what I found, not so with power supplies, except for one new design that couldn't handle 110v off a wye vs delta back at the 440v poles without feedback every 6 hours as an IC got hit hit with a perfect "stop" command.

   This is the only wart plug Ive seen with the die cut prongs; I thought it was unusual too ......when it was new and had no carbon on it.  But thanks for your confidence in my word on that FACT too. When you see another, think of me

..sigh...I'm usually such a fan of Occums razor too. You folks are weilding it like a hatchet, and discounting anything I have to say...have fun...TRY to be safe

John's expaination makes sense, but is not the only way to get arcing at a plug.

Experience, other than this one, tells me that. I however have no explaination for those cases either.

Forum dialog is only a portion of any conversation,  so much more can be ascertained face to face.  I'm with 3rail 2, this is amusing.  I remember when I was a child my parents caught me in a lie but I insisted I was right.  As a 6 yer old, I just could not admit my culpability.  Anyone on board here ever read the book "BLINK"? Somewhat intriguing.

Ed Diem.  I believe you will find the ground prong position rule for commercial application in the NEC.  On residential jobs the electrician asks us if we want the smiley face (ground down).  On commercial jobs I am told there is no option.  One of the initial concerns mentioned was a metal face plate coming loose and dropping onto the prongs.

If I ever learned one thing on OGR, place your bets on GRJ.  Both his theory and practical is spot on.

I agree, my conclusion is not the only way you could get arcing at a plug, a poor connection would do it, a power surge of sufficient size would do it, etc.  However, when you add all the elements that we got to see in your pictures, the obvious conclusion I come to is the chain shorted the prongs.  I'll bet money if that event caused a fire and a fire marshal had that in front of him, he'd come to the same conclusion that I did.  

If you allow for clues that we didn't see in the pictures, it's certainly remotely possible something else happened, we'll likely never know.  Again, those pictures are all we had to go on, and that's what we based our conclusions on. 

FWIW, you'll hear this from multiple sources, eye witness observations are notoriously inaccurate, many times you think you saw something other than what happened.  This happens to everyone, so I'm not singling you out, it's just the way we're built.  I've chased issues where I would have swore that I checked something a dozen times, only to find that the obvious cause was in fact the actual cause, I just somehow refused to see it.

  I saw, I told, and didn't try to hide anything. I've answered including possibility of doubt, though admittedly  slim.

I think some evidence is still being ignored by some.

  I'm not upset with John one bit because he is nearly the only one to acknowdge a remote possibility along with his conclusion. Nobody seems to notice that. 

That's all I asked for; thought. A fluke? An accident ? Hopefully.

Do you home or industrial electricians ever run into blind spots/cancellations or suddenly realize the phazing isn't what you expected. You don't know how many times I've seen it wrong or found dead legs after using outside contractors who only see one type of drop or another in an area and pull, wire, but don't test. Running new wire doesn't really count so much as your trouble shooting ability if it is already ran.

  I'm upset because of those with so much less experience, not just making light of a warning,.."ok thanks",  but for issuing a ****ation of possibilities without first considering them. 

What if I did see a rare event and kept quiet? Then I'd be the idiot that didn't speak up, experienced or not.....  You're welcome.

  I can still reproduce the thermal overheat on an unconnnected wire laid across a diode. When I move them apart, the power supply stays on, and the diode cools. It really shouldn't happen.  I could try to show you; but then again, I could easily stage all the photography too, infrared temp and all. Especially now, I'll just tell you and hope that you believe. 

 Buildings full of children didn't ever have me taking serious things lightly either. But there is always room for joke about the little stuff.  I've never been fired or repremanded from a tech job, only promoted, sometimes much to the dismay of those with degrees; and those doors are still open if I could manage it. You're all welcome for the lowest downtimes and the cleanest stores that never made the news, with never a bypassed saftey concern. Explained or not, I'd avoid recreating the circumstances if it hppened there too.

 I worked in test rooms around live 2x8" 480 buss bars at your feet like railroad track. I'm still not clumsy, I have a very deliberate movement, it's not often I spaz or am inattentive. You don't apply for that so much as you are invited and have to sign confidentiality papers.

  Did anyone even read the saftey notes on plant wide communications concerns and note induction was included there? That's not enough to warrent thought about it? Because its not in a home or what? If you don't understand at least the basics, the comments are mindless trolling.

   I am not accustomed to being compared a lying child Tom; thanks for that, and more so for your looking beyond the obvious evidence for another cause.

Maybe you should take a note on the face to face bit combined with experiences directly with folks as a better way to make judgement on someones integrity than a book on stereo typing. The body language stuff isn't 100% either by the way.

   Instead, try reading up on high functioning Asperger's and short term vs long term memories of a photographic nature. My memories tend to grow sharper with time. That is more the norm for me, and the info would apply better here. My stance is set with my visual memory of the event. I could be wrong, but I know were the odds lay; IMO, I'm not wrong about the chain.

Dog drool, my sweat, a single, fine, stray wire strand, internal bridging, are also high high on the list of possible shorts. Higher IMO...espcially the liquids as it and vapor are as good an explaination for the carbon trails along the low volt is as good as any.

Grampstrains posted:

... utility companies ask people with generators to disconnect the main breaker in the house to prevent a backfeed on the lines.  This is a safety hazard for the linemen.

Oh no, no utility would give this advice. An isolation/transfer switch is necessary. The breakers cannot  be counted on as service disconnects, and there cannot be any  room for operator error in remembering either the position or order of operation of a panel breaker in an effort to back-feed a panel from a generator.

One conclusion can be drawn from the above discussion:  Whenever any plug or wallwart or other device with prongs is plugged into any electrical receptacle, whether in a wall or at the end of an extension cord, conductive materials should be kept away from that area.

gunrunnerjohn posted:

Once you let the magic smoke out, there's no covering it up!

Ah,,,,,.......the old "smoke and mirrors" trick.

I see this all the time from my structural and civil Engineers!!!

Works every time.

Donald

Reading this I am seeing a lot of different thoughts, and few saying they will keep that in mind. The only thing I know for sure is that what Adriatic may be possible, but I am not an electrical engineer, nor do I have a degree regarding anything electrical. I for one do not blame him for not wanting to try to replicate the problem, that can cause more problems.

My though it Electricity can be unpredictable, doing pretty much what is wants how it wants, we can kind of control, but there is a lot of variables. The only background I have in electrical equipment is my job I have done, building and testing components for elevators, as well as some for computers, since I have built my own computers, and my own Ethernet cables. As well as my other hobby that usually doesn't use more than 11 Volts at most, most of the time it is 7.4 V DC or less and maybe 3 Amps at most, but rarely that high.

I have been reading it and I says thanks for the information, and I will keep a look out, because you never know, it could happen.