AIC rating of laptop...

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e57

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Posted on another forum is a link to an interesting 'Cable Guy' story. As links dont really work here anymore, It is summerized below: What do you think he connected to? And do you think it was capable of this damage.

I ordered high speed broadband internet from the local cable company. On November 16, 2006 a technician arrived to install it.

He connected the coaxial cable that was coming into the wall from outside into a cable modem for Mac. He then connected an Ethernet cable out of the modem and into my fully loaded Apple 15? Powerbook.
After over an hour, and with the installation CD still spinning in the laptop, the technician said he still could not get the proper signal into the modem/computer. He said he was going to trace the coaxial cable from the wall up onto the roof and see if he could solve the problem.

About 10 minutes later I was standing on the back porch just outside the window of the computer work desk when I saw a bright flash of light accompanied by a very loud explosion at the work desk. It was as loud as an illegal M-80 on the Fourth of July. After being stunned and confused for several seconds, I ran inside my home into a thick cloud of grey smoke which smelled like gunpowder. Then I ran outside and yelled for the technician, thinking that perhaps he had been electrocuted.

Everything on the desk was blackened with soot and burned either partially or completely. Three external hard drives, a digital camera, videotapes, papers, CD?s, etc. The floor, wall, and radiator cover were burned, along with the tabletop.

Every cable that was connected to the laptop, Ethernet, Firewire, Power, and USB, was forcibly shot out of each portal, and each portal covered with the black soot. Metal bits and electronic debris from the power cable hub and other cables was scattered around the room and some wires had split apart into copper shreds. Molten silver metal flecks are still lodged in the windowsill.

A supervisor arrived later that day and after surveying the scene and materials, conceded that their company had caused the accident. He noted, in particular, the internally fried coaxial cable.

It seems likely that the young technician connected the rooftop end of the cable to a similar-appearing, but now obviously incorrect electrical cable. In any case, both technicians stated that the company-installed ?system? of cables on the roof were ?a real mess? and were unsafely stretched over and near an electrical box and associated cables.

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http://www.macwork.com/2006/12/09/m...w-the-cable-company-incinerated-my-powerbook/
 

Jraef

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I'd bet this is another urban myth being started. There is nothing I can think of that would be a "similar-appearing, but now obviously incorrect electrical cable" to which anyone in their right mind could find a way to connect to a coax cable. And at best, they coupld connect to what, 120V? Not likely to be that explosive. This hoax was concocted by someone who has little or no knowledge of electrical installations or equipment.
 

don_resqcapt19

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Jeff,
I tend to agree with you. The computer equipment is connected to the cable modem by the ethernet cable and there is internal isolation between the coax and ethernet cable in the modem.
Don
 

e57

Senior Member
Jraef said:
There is nothing I can think of that would be a "similar-appearing, but now obviously incorrect electrical cable" to which anyone in their right mind could find a way to connect to a coax cable. And at best, they coupld connect to what, 120V?

Imagine an RG-6Q connector on a #4-2 AL service conductor, and think arc flash/blast....
 

don_resqcapt19

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e57,
Imagine an RG-6Q connector on a #4-2 AL service conductor, and think arc flash/blast....
The current would be very limited by the impedance of the conductors and 120 is unlikely to jump across the burned parts of the modem. I could buy that the modem smoked and maybe even had case damage, but I can't buy the current jumping on the cat5 and causing the damage to the other equipment.
Don
 

tallgirl

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don_resqcapt19 said:
e57,

The current would be very limited by the impedance of the conductors and 120 is unlikely to jump across the burned parts of the modem. I could buy that the modem smoked and maybe even had case damage, but I can't buy the current jumping on the cat5 and causing the damage to the other equipment.
Don

Dittos. Cat5 is something like 28AWG (quick, where's a roll of Cat5 when I need one) and its not going to carry the current needed to do all that damage, short of if hit by lightning. On top of that, neither are USB cables for the 3 external disk drives, which I assume from the photo of the smoked USB cable were connected via USB cables and not something phat like a 50 conductor SCSI cable.

For all that to happen, the PC board traces would have had to support all that current, in both the modem and laptop, with the fried chips still being un-fried enough to continue conducting. Not very likely that happened.
 

e57

Senior Member
This is my post from the ECN thread on this topic:
I think it is quite possible as mentioned for an "Ordinary" 120 drop on the POCO side of a main breaker to do just this type of damage. No 'freak of nature' or high voltage... Just 120 at several thousand amps vaporizing a very narrow path to ground in a microsecond... (A ball of super-heated metalic gas) Admittedly the scenario is strange, but not so far out there, IMO. There a lot we don't know about the incident, but having seen a POCO side short at 120 up close remove roughly 9 square inches of 14g steel in a simular explosive detonation, I'm gonna pull a 'mythbuster - plausable' on it. And not that I would suggest anyone try this at home.... (Without proper PPE and notification/participation of your local POCO) I don't think the RG-6 impedance would make any noticable at all at with that amount of energy.
 

don_resqcapt19

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e57,
Just 120 at several thousand amps vaporizing a very narrow path to ground in a microsecond...
The 'very narrow path" is the problem....several thousand amps can't flow on that path at that voltage.
....I don't think the RG-6 impedance would make any noticable at all at with that amount of energy.
Have you ever looked at the short cicuit calculations to see how much the current is reduced by the impedance of the conductor? Using the short circuit calculator on the Bussmann site, if you start with 10,000 amps available short circuit current and run 50' of #14 in a non magnetic raceway, you only have 452 amps available line to neutral at the end of the run. Even if I take the available current up to 50,000 amps at the start of the run, the line to neutral available current at the end is only 464 amps. The impedance of the coax will be much much higher than than of #14 copper and reduce the available current even move. Note I used single conductors in non-magnetic conduit because that is the closest match for NM that they have on the calculator.
Don
 

kingpb

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I would have to agree with Don. Likewise, the damage seems much more extensive then would be consistent with the described situation.

One thing I've learned, there are always two sides to every story.
 

e57

Senior Member
Don RG-6's impedance value is based on the center conductor vs the shield and the capacitive effect between the two - if this was on the shield, or likely both, due to skin effect of the current travel you would have something the equivilent of #2 as a path to ground. (Remember the cable was not used as a limited conductor carrying a CATV signal) And the paths to ground could be anywhere... Via the hub to anything (all paths) connected to it, to a phone or DSL modem, computer power supply, through other RG6 connections...

We'll agree to disagree, but I'll maintain that it happened exactly as decribed with the given details.....

____________________________________________________________

I'll add a correction - something equivilent to #4-3...
 
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RG-6 is about the same size as #14. I checked it with my wire strippers. One time when I used to be a CATV installer, I was doing a routine reconnect. Nobody was home and my instructions were to just turn it on outside. I saw a little spark when I screwd on the connector. As I was walking away I smelled something burning. The insulation on the RG-6 was melting from the ground block to the tap on the main line. But from the ground block going into the house, nothing was happening. I disconnected the ground wire from the POCO equipment and the burning stopped. I don't know what the outcome was because I called the cable company and told them to have one of their techs look at it.
 
Anyway, with CATV the code says that we must bond to the POCO equipment. We used #10 bare copper to accomplish this. The ground block is a solid part, kind of a small bus bar with two male coax connections coming out of each side. The aerial or lateral CATV cable attached to one side and the home run into the house attached to the other. The shield around the cable is in contact with the connector which is in contact with the ground block which is bonded to the grounding electrode system of the POCO equipment. The center conductor is completely isolated from the shield. If this isolation is broken the center conductor would start to carry radio and TV signals that are picked up on the outside shield. This is called ingress and would cause rolling diagonal lines on your TV picture. Anyway I was thinking, what if something is wrong with the neutral in the panel, wouldn't the current try to return through the grounding electrode? If so, this would energize the cable equipment. Even the CATV taps at the pole are connected to steel cables that are also connected to the guy wires that go to the ground to hold up the poles.
 

coulter

Senior Member
E57 -I'm trying to get a handle on the physics of this.

e57 said:
...Just 120 at several thousand amps vaporizing a very narrow path to ground in a microsecond...
How can several thousand amps be delivered from a house service? A 15kVA 5%Z will deliver 1200A SC at the xfmr - quite a bit less at the end on a service drop.

Microsecond? A quarter cycle at 60Hz is 4miliseconds, about 4000 times longer. Are you suggesting there was a high frequency/high current event?

e57 said:
...RG-6's impedance value is based on the center conductor vs the shield and the capacitive effect between the two - if this was on the shield, or likely both, due to skin effect of the current travel you would have something the equivilent of #2 as a path to ground. ...
I don't see the physics of this at 60HZ - maybe at 2000MHz that might be true. Do you have any references on this? Or again, are you suggesting there was an unknown type of HF event?

e57 said:
...Imagine an RG-6Q connector on a #4-2 AL service conductor, and think arc flash/blast....
IEEE 1584 says one can discount arc flash/blast for xfmrs less than 125kVA or voltages less than 208V - which pretty well leaves out house services. What is the suggested source for the driving energy for this event?

e57 said:
...I'll maintain that it happened exactly as decribed with the given details...
Are you saying you have first hand eyewitness evidence?

I'm really struggling with the physics and science here - please help me out.

carl
 

tallgirl

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e57 said:
Don RG-6's impedance value is based on the center conductor vs the shield and the capacitive effect between the two - if this was on the shield, or likely both, due to skin effect of the current travel you would have something the equivilent of #2 as a path to ground. (Remember the cable was not used as a limited conductor carrying a CATV signal) And the paths to ground could be anywhere... Via the hub to anything (all paths) connected to it, to a phone or DSL modem, computer power supply, through other RG6 connections...

We'll agree to disagree, but I'll maintain that it happened exactly as decribed with the given details.....

Don's numbers came straight from the Bussman website's short circuit current calculator. I went there as well and that's pretty much what I got when I fed in umpteen zillion amps and 50' of #14.

The problem I still have is that many of those paths won't carry much current at any kind of voltage at all. Those traces are designed to carry milliwatts, not tens of kilowatts, which is what ISCA x V is going to yield. With very little thermal mass, those traces will vaporize fairly quickly, and then the circuit is open and the entire event is over.
 
The equipment cabinets which are grounded can carry those currents. Since the event is over, we really don't know how much current that was. It really doesn't take much to fry electronic equipment. The whole huge explosion thing is probably an exageration though. One of the devices may have burned and put soot all over everything else. I don't believe the current would have traveled through everything for very long. A power surge could destroy the rest of the equipment. Since internal electronics usually operate on 5V DC, it wouldn't take much to destroy all those devices.
 
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e57

Senior Member
coulter said:
E57 -I'm trying to get a handle on the physics of this. Sure... Bear in mind that we do not know all of the specifics.

How can several thousand amps be delivered from a house service? A 15kVA 5%Z will deliver 1200A SC at the xfmr - quite a bit less at the end on a service drop. Pretty small can for most neighborhoods in my area... Most urban distribution here is 45-75 kva or more.

Microsecond? A quarter cycle at 60Hz is 4miliseconds, about 4000 times longer. Are you suggesting there was a high frequency/high current event? You get what I mean right? :rolleyes:

I don't see the physics of this at 60HZ - maybe at 2000MHz that might be true. Do you have any references on this? Or again, are you suggesting there was an unknown type of HF event? Nope - 60hz

IEEE 1584 says one can discount arc flash/blast for xfmrs less than 125kVA or voltages less than 208V - which pretty well leaves out house services. What is the suggested source for the driving energy for this event? Discounts in terms of PPE, etc... Although one can discount the calculations, one should not discount the dangers involved, although flash/blast would be relitively small in comparision - but should still not be discounted.

Are you saying you have first hand eyewitness evidence? Ever short a 120 service conductor? I have, it removed roughly 9sq" of 14ga steel and went off like a grenade. Looking, sounding, and smalling much like what is described in this incident....

I'm really struggling with the physics and science here - please help me out. I'll let you do the math....

carl

Sorry, dont know how to chop up individual quotes, my comments in red...

Anyway, as I described before, this is what I imagine happening, as said before there is not a lot known about this, but as described... I see it as entirely possible. Say you have some Cable Guy out there.... He's "tracing" a circuit, and sees something looking like an unterminated RG-6 drop - says to himself, "Well there's your problem" reaches over and terminates a F-connector to a 120v 60hz service drop - (or for that matter anything else of a simular size and jacket color...) Takes his RG-Q and puts a coupling on it, then atempts to put it on the unknown conductor he just blindly put an F-connector on. We dont know what the transformer was, or its distance, or the distance of the cable to these pictured items so I am not going to speculate on that. I am only saying that as described, this is totally possible!

Break out your calculator...
Lets say it was a ?? kva pot (Choose a size) about 100' away from the house fed on a #4 triplex. (Feeding the neighbor too) And lets also say that the RG-6Q run was about 50' from this equipment. Lets also say that both the shield and center conductor of the RG-6 are energized. Ignore the listed 75ohm impedance of the cable, as that is based on the capacitive effect of the grounded sheild that is now energized as a tubular conductor. As you may know about skin effect of ac on conductors - most of the current would be concentrated in the sheild as on regular conductors it is concentrated on the extrerior of the conductor. The shield is roughly the same as #6 in cross-section, but as a tube its outside diameter is roughly #1. So for the sake of argument/discussion lets call it #4 in terms of current carriying capabilty, and resistance... So 150' of #4??? Who knows what a return path would be??? This is not a normal calculation so wing it..... Find a short circuit calc for that in amps - calc wattage for that for sake of determining how much heat that is for a single cycle - or half or quarter cycle if you like. Convert it to BTU if you like....

Not trying to be quirky - but this is not a normal calc that can be broken down easily with the [rummy]known unknowns[/rummy].... :roll:
 

hillbilly

Senior Member
Just a thought....
What if the cable guy did somehow power the co-ax to 120V and that (somehow) caused the battery in the lap-top to short between cells and explode.
How much energy would that produce?
I've seen a automobile battery explode before, and it's scary.
Is that possible?
steve
 

rattus

Senior Member
hillbilly said:
Just a thought....
What if the cable guy did somehow power the co-ax to 120V and that (somehow) caused the battery in the lap-top to short between cells and explode.
How much energy would that produce?
I've seen a automobile battery explode before, and it's scary.
Is that possible?
steve
Laptop batteries have been known to start fires, but it sounds like the installer somehow connected the cable to 120V which would fry a lot of things and perhaps create a short to the battery which would then explode.
 

Bob NH

Senior Member
One test is worth at least 100 speculations and analyses that have no real data.

One of the first principles of failure analysis is to try to reproduce the failure under known conditions. Anyone have a Mac to offer for the test?

Is it beyond comprehension that a tech might do something like that intentionally to "see what would happen"?
 
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