Author Topic: How long would it take to replace all the electrons in a piece of wire?  (Read 6447 times)

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Offline TerraHertz

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Re: How long would it take to replace all the electrons in a piece of wire?
« Reply #25 on: February 08, 2017, 02:35:04 am »
Enclosed are a couple of pictures of the aftermath after some hapless electrician burned through two ΒΌ inch thick layers of copper bus bar with a little over 500 volts DC from a big bank of lead acid batteries of a 750 KVA UPS installation.

Looks like the experiment was inconclusive. Lucky you have a second panel over to the left to try it again. This time take a video?
Collecting old scopes, logic analyzers, and unfinished projects. http://everist.org
 

Offline T3sl4co1l

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Re: How long would it take to replace all the electrons in a piece of wire?
« Reply #26 on: February 08, 2017, 04:14:49 am »
Yikes!  Was that just the arc flash, or was it sustained (poorly fused, or unfused for that matter  :o )?

Having worked on 480VAC industrial equipment myself, I can simply say this:

Don't fuck around.  Treat it carefully, with respect.

Fuses are there for a reason, and guards, PPE, and safety procedure are there for a reason.

Don't die.

Tim
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Offline bson

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Re: How long would it take to replace all the electrons in a piece of wire?
« Reply #27 on: February 08, 2017, 04:35:53 am »
The problem with electrons is you can't have only one.
 

Offline Gregg

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Re: How long would it take to replace all the electrons in a piece of wire?
« Reply #28 on: February 08, 2017, 04:36:58 am »
It was DC fed by the battery bank which was connected prior to landing the wires in the disconnect cabinet.  It should have been connected in the cabinet first and every wire tested with a meter prior to final connection.  The battery bank is capable of thousands of amps for many minutes and because it is DC the arc sustained itself until the wire and bus bar burned far enough apart to stop.  The batteries are about 20 inches wide and 24 inches tall; the cables are parallel 750 MCM. 
 

Offline station240

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Re: How long would it take to replace all the electrons in a piece of wire?
« Reply #29 on: February 08, 2017, 04:12:59 pm »
Disregarding the 'all electrons are the same one' mind-bender, the answer is... forever.
Because only the outer shell electrons are free to move in the solid. Regardless that those ones only drift very slowly (less than walking pace) under an applied field, the vast majority of the metal atom electrons are not going anywhere.

My thoughts on the matter also, it's not possible to replace all the electrons.
A copper atom has 11 valence electrons, in the two outermost valence shells.
But it has 29 electrons, so you can only replace 38% of the electrons.
 

Offline T3sl4co1l

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Re: How long would it take to replace all the electrons in a piece of wire?
« Reply #30 on: February 08, 2017, 04:23:15 pm »
It was DC fed by the battery bank which was connected prior to landing the wires in the disconnect cabinet.  It should have been connected in the cabinet first and every wire tested with a meter prior to final connection.  The battery bank is capable of thousands of amps for many minutes and because it is DC the arc sustained itself until the wire and bus bar burned far enough apart to stop.  The batteries are about 20 inches wide and 24 inches tall; the cables are parallel 750 MCM. 

So there's no fusing at the battery?

If it was me, I'd want a fuse on there, early and often... even just while wrenching it together.

But I don't know what SOP is, as far as distributing and fusing such sources.

My thoughts on the matter also, it's not possible to replace all the electrons.
A copper atom has 11 valence electrons, in the two outermost valence shells.
But it has 29 electrons, so you can only replace 38% of the electrons.

With zero energy barrier to the exchange*, it would be foolish to think the electrons wouldn't swap constantly between locations! ;)

*Again, assuming one could ID electrons, which one cannot; for the same reason, the electrons on Pluto have zero energy barrier to exchange with the electrons in any wire, or any other combination of exchanges.  They're all identical!

Also also, copper "gives up" about one electron per atom, to the conduction band, so it wouldn't be quite correct to estimate the quantity of free electrons as the valence band, either.  But again -- it doesn't matter -- there's only ever been one electron, for all matter, for all time!  (Even the occasional positron is just an electron rewinding backwards through time!) :D

Tim
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Offline Gregg

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Re: How long would it take to replace all the electrons in a piece of wire?
« Reply #31 on: February 08, 2017, 09:32:22 pm »
Tim,
The battery current protection is the breaker in the cabinet.  It is a shunt trip breaker that the UPS controller can trip if there is a problem as well as standard breaker function of being able to manually turn it off for things like battery maintenance.  The breaker is located within 10 feet of the connection end of the battery string.  Usually there are two parallel connected redundant UPS units feeding the same load so that one at a time can be taken off line for maintenance.  Sometimes two battery strings, each with their own shunt trip breaker are connected to each UPS unit to allow for battery maintenance. 
The pictures were from a new installation at a data center.  Standard procedure is to connect the DC cabling to the breaker cabinet before connecting the battery end.  Then at the battery end everything but the battery terminal plate being connected gets blanketed from all other terminals and ground.  Then each cable is checked with a volt meter and ohm meter to ensure the correct cable is connected to the proper terminal.  The cables should be labeled on both ends during installation, but still must be double checked with a meter.
This incident didn't happen on one of my projects and the contractor was banned from the job.  (I retired from the power end of electrical engineering working for a large data / telco / cellphone company.)  I used to print some of my pictures to show contractors why they needed trained people on the job. 
In operating facilities there are standard and custom SOWs (scopes of work) that delineate step by step the procedures for almost anything that may affect the network and most of this stuff gets done between midnight and 5 AM.  On new construction, however, there isn't as much oversight as was the case here.  If an electrician that has only household and light commercial experience and thinks that this stuff is the same only with bigger wires is turned loose on something with over 500 volts of DC and over 10K amps available their first mistake may be their last.  Luckily the guy that vaporized the bus bar survived but did suffer some severe burns to his face and arms.  Stupidity should be painful, too bad his supervisor didn't get to share the pain.
I have lots of good stories of how not to do things.

 

Offline T3sl4co1l

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Re: How long would it take to replace all the electrons in a piece of wire?
« Reply #32 on: February 08, 2017, 10:42:39 pm »
Ah, yeah, that sounds good.

Guess I can't say nobody got hurt, but at least nobody died either!

Don't be afraid to share your wisdom.  There's no shortage of newbies here, some of whom may be going into power and electrical jobs some day. :)

Tim
« Last Edit: February 08, 2017, 10:45:59 pm by T3sl4co1l »
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