Author Topic: Interesting and sad case of electrical injury  (Read 4183 times)

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Offline zapta

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Re: Interesting and sad case of electrical injury
« Reply #50 on: May 26, 2024, 04:30:31 pm »
       I spend a few years working with 12,000 volt systems and later spend 4 years working on U.S.A.F. Search RADARS ..

Did you use to clap behind the back of people working on high voltage?

We did.
 

Offline temperance

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Re: Interesting and sad case of electrical injury
« Reply #51 on: May 26, 2024, 05:15:16 pm »
Quote
Did you use to clap behind the back of people working on high voltage?

We did.

How funny. I had a colleague who like to do just that when I was working on a 5 kW +200 -200 V SMPS. He tried it twice. The third time I pushed him into a cabinet. He told me I wasn't normal.

Later on he electrocuted himself by grabbing the busbars of 3 phase powered system while the thing was still plugged in. One burned tendon later, he's probably still having trouble masturbating.
 
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Offline Marco

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Re: Interesting and sad case of electrical injury
« Reply #52 on: May 26, 2024, 05:37:12 pm »
When looking at the Fluke 28, he points to the large PTC and identifies it as a MOV, that is basically the front end I would expect to see.   

So to hold off the allowed transient indefinetely you'd either need a large string of PTC's in series, or disconnect the ohm/diode path with the selector switch. Also the series resistance for the Voltage path to the MOV's would need to be 10+ Meg to keep dissipation reasonable. Doable, but maybe not having the meters blow up until even more dangerous voltages would just cause more dangerous behaviour.
 
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Online Harry_22

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Re: Interesting and sad case of electrical injury
« Reply #53 on: May 26, 2024, 06:44:04 pm »
I was somehow struck by Wimshurst machine while having fun.
The next day I was admitted to the hospital with atrial fibrillation.
 

Offline jitter

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Re: Interesting and sad case of electrical injury
« Reply #54 on: May 26, 2024, 07:30:20 pm »

Not sure why you thought to add to the conversation.

Because you claimed to have measured more than 10X higher at your parents home. 

And why not? It all depends on the impedance of the wiring between your distribution board and the transformer.

I live pretty close to a distribution station, but the people living right nextdoor have a (calculated) wiring impedance of just 23 mΩ. If my calculation is correct, then they should have a short circuit current of about 10 kA at their board.

« Last Edit: May 27, 2024, 05:31:07 am by jitter »
 

Online coppercone2

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Re: Interesting and sad case of electrical injury
« Reply #55 on: May 26, 2024, 07:52:30 pm »
making decisions not based on the standards is a bad idea even if your current is lower because the power co can always change things, especially with EVs and stuff requiring more power. you might have a drastically changed situation if they do upgrades

I.e. i see in pheonix they put these ugly ass towers up for mains to support grid load on AC and EV where there is not enough local storage and very high peak demands. they might be getting some scary fault currents there now. it looks like thick 'pylons' in a residential neighborhood in peoples backyards.
« Last Edit: May 26, 2024, 07:54:05 pm by coppercone2 »
 

Offline SeanB

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Re: Interesting and sad case of electrical injury
« Reply #56 on: May 26, 2024, 08:06:23 pm »
I have seen a Fluke 77 that was returned "under warranty" because the arctrician tried to measure the primary side of a 11kV distribution transformer, and  just grabbed the meter, and a long stick ( some thought there) to hold the probe near the connection. Inside the case was copper plated all the way down from display to input jacks, and there was no more copper on the board, other than the copper by components under the soldering. All blown off the soldermask, leaving bare board behind. Meter did not power on at all, the Fluke ASIC was there, missing the top of the package, and the thick film resistor network was cracked, and the resistors in it had marks of flash over on them for the input side one. Fuses were intact, along with the 9V battery, and the display was still working, put into another meter to verify, as that one was there because they had broken the display. Meter was scrapped, and the broken leads were also cut to pieces. New meter sent, along with the bill. I was still in school, visiting the one place that was a RS distributor (when RS catalogues were still the only way to get data sheets or more exotic IC's, and a 2 week wait for them to arrive) and which is still running these days.

By me the distribution transformer (200kVA, is 50m away, 300m cable wise, and the cable itself probably dates from 1900 in places, being the original paper insulated cable, and the feed to me is only around 60 years old, well worn SWA paper insulated and oil filled, complete with lead wiped ends. 400A fuses by the substation, a standard size, though there are still a good number with 200A fuses, that date from the 1950's, still in use, only replaced when they blow, and they will not blow for 400A of load as evening peak, measured that one evening.
 
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Offline 44kgk1lkf6u

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Re: Interesting and sad case of electrical injury
« Reply #57 on: May 26, 2024, 10:42:16 pm »
Did you use to clap behind the back of people working on high voltage?

We did.

Why?  Was it to scare them?
 

Offline johansen

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Re: Interesting and sad case of electrical injury
« Reply #58 on: May 26, 2024, 11:00:10 pm »
Did you use to clap behind the back of people working on high voltage?

We did.

Why?  Was it to scare them?
we had no tolerance in the usmc for that bullshit.
 

Offline joeqsmith

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Re: Interesting and sad case of electrical injury
« Reply #59 on: May 26, 2024, 11:59:59 pm »

Not sure why you thought to add to the conversation.

Because you claimed to have measured more than 10X higher at your parents home. 

And why not?

Sorry, why not what? 

Offline joeqsmith

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Re: Interesting and sad case of electrical injury
« Reply #60 on: May 27, 2024, 12:15:42 am »
When looking at the Fluke 28, he points to the large PTC and identifies it as a MOV, that is basically the front end I would expect to see.   

So to hold off the allowed transient indefinetely you'd either need a large string of PTC's in series, or disconnect the ohm/diode path with the selector switch. Also the series resistance for the Voltage path to the MOV's would need to be 10+ Meg to keep dissipation reasonable. Doable, but maybe not having the meters blow up until even more dangerous voltages would just cause more dangerous behaviour.

That HV probe I made up for example is 400Meg but the resistors have a limited life.   Using non-contact would be better.
 

Offline johansen

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Re: Interesting and sad case of electrical injury
« Reply #61 on: May 27, 2024, 12:18:54 am »

Not sure why you thought to add to the conversation.

Because you claimed to have measured more than 10X higher at your parents home. 

And why not?

Sorry, why not what?
this ain't your grandma's outlets.

a typical industrial 120/208 system has a 10,000 amp fault current, and on industrial buildings they stencil the short circuit current on the panel.. -of course if you add in .25 ohms from 100 feet of 14 gauge wire then the short circuit current drops to what you measured, 390 amps.

but lets imagine you now have a 4000 volt service. suddenly that additional .25 ohms doesn't really do much to limit the current! not to mention the wires in a 4000 volt system will likely be nothing less than 6 gauge.

my house drops 4 volts at 60 amps, for a 3600 short circuit current, i'm about 60 feet of 4/0 aluminum cable direct to a pad mount 25kva transformer.

Attached is a photo of the transformer

Those wires sticking up out of the ground are live. I was able to stab them with my multi meter leads and measured a 3.6 volt drop at a 63 amp load.

meaning 90% of the voltage drop is in the transformer. this is typical of a 25kva transformer.

my neighbor had the power cut to her shed (it was a separate utility drop) i'm pretty sure they decided to just dig up the line and cut the cable and cap the ends, rather than pull the meter (which they didn't) --i've never seen bare wires left up out of the ground like this before but prior to this thread i wasn't inspired to mess with them.


« Last Edit: May 27, 2024, 12:27:46 am by johansen »
 

Offline joeqsmith

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Re: Interesting and sad case of electrical injury
« Reply #62 on: May 27, 2024, 12:25:36 am »

Not sure why you thought to add to the conversation.

Because you claimed to have measured more than 10X higher at your parents home. 

And why not?

Sorry, why not what?
this ain't your grandma's outlets.

a typical industrial 120/208 system has a 10,000 amp fault current, and on industrial buildings they stencil the short circuit current on the panel.. -of course if you add in .25 ohms from 100 feet of 14 gauge wire then the short circuit current drops to what you measured, 390 amps.

but lets imagine you now have a 4000 volt service. suddenly that additional .25 ohms doesn't really do much to limit the current! not to mention the wires in a 4000 volt system will likely be nothing less than 6 gauge.

my house drops 4 volts at 60 amps, for a 3600 short circuit current, i'm about 60 feet of 4/0 aluminum cable direct to a pad mount 25kva transformer.

I'm sure your trying to make a point but it's lost on me.   I provided the data I collected from our home for a reference.   This was measured not calculated.   I've already explained there is no 4000V service feeding into our home. 

Offline johansen

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Re: Interesting and sad case of electrical injury
« Reply #63 on: May 27, 2024, 12:29:02 am »


I'm sure your trying to make a point but it's lost on me.   I provided the data I collected from our home for a reference.   This was measured not calculated.   I've already explained there is no 4000V service feeding into our home.

the whole point of this thread regards why electrical meters blow up at 4000 volts.

turns out 20,000 amps will do it?

somehow you're not convinced that could happen?
 

Offline joeqsmith

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Re: Interesting and sad case of electrical injury
« Reply #64 on: May 27, 2024, 12:35:08 am »


I'm sure your trying to make a point but it's lost on me.   I provided the data I collected from our home for a reference.   This was measured not calculated.   I've already explained there is no 4000V service feeding into our home.

the whole point of this thread regards why electrical meters blow up at 4000 volts.

turns out 20,000 amps will do it?

somehow you're not convinced that could happen?

I think you're reading more into my posts than what is there is all.

Offline Monkeh

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Re: Interesting and sad case of electrical injury
« Reply #65 on: May 27, 2024, 12:36:00 am »
I'm sure your trying to make a point but it's lost on me.   I provided the data I collected from our home for a reference.   This was measured not calculated.   I've already explained there is no 4000V service feeding into our home.

 |O

The 5kA mentioned before would be between both legs of the phase, at 240V, at the origin of the installation. Whether you have 4kV at home or not isn't really relevant to his post.
 

Offline joeqsmith

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Re: Interesting and sad case of electrical injury
« Reply #66 on: May 27, 2024, 12:38:15 am »
I'm sure your trying to make a point but it's lost on me.   I provided the data I collected from our home for a reference.   This was measured not calculated.   I've already explained there is no 4000V service feeding into our home.

 |O

The 5kA mentioned before would be between both legs of the phase, at 240V, at the origin of the installation. Whether you have 4kV at home or not isn't really relevant to his post.

He never posted how it was measured or at what location.   I did provide that detail.

Offline johansen

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Re: Interesting and sad case of electrical injury
« Reply #67 on: May 27, 2024, 12:42:37 am »
I'm sure your trying to make a point but it's lost on me.   I provided the data I collected from our home for a reference.   This was measured not calculated.   I've already explained there is no 4000V service feeding into our home.

 |O

The 5kA mentioned before would be between both legs of the phase, at 240V, at the origin of the installation. Whether you have 4kV at home or not isn't really relevant to his post.
This is all turning into a gigantic waste of time, but at least i was inspired to find out if the wires sticking up out of the ground on my neighbor's side of the road are live.

100 feet of 14 gauge wire (50 feet from your panel) is enough resistance that you can safely touch the wires together in front of your face and you will not be blown across the room by the expanding metal vapor cloud at 50,000 degrees kelvin!

here is a classic 480v clip
« Last Edit: May 27, 2024, 12:44:21 am by johansen »
 
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Offline joeqsmith

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Re: Interesting and sad case of electrical injury
« Reply #68 on: May 27, 2024, 12:57:39 am »
It's not like we have not discussed fault currents and arc flash before.  Normally I have no interest but I am still curious about Marco's original question, which is what prompted me to post. 

Offline johansen

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Re: Interesting and sad case of electrical injury
« Reply #69 on: May 27, 2024, 01:05:31 am »
What actually happens to a CAT-III 600V Fluke if you connect continuous 4kV to it?

i fully expect it to explode.

two cheap meters, a VC-99 and an older 2000 count meter survived 1999 volts on a slow rise time, but the 2000 count meter blew up when i reversed the polarity suddenly. -pretty sure i did not test the vc-99 the same way after the other one blew up.
« Last Edit: May 27, 2024, 01:09:40 am by johansen »
 

Online Someone

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Re: Interesting and sad case of electrical injury
« Reply #70 on: May 27, 2024, 02:08:58 am »
It's not like we have not discussed fault currents and arc flash before.  Normally I have no interest but I am still curious about Marco's original question, which is what prompted me to post.
Orly? how about the post quoted in full:

...
An average 120/240 system on a larger building has a short circuit current of 10,000 amps depending on the size of the pole transformer and length do the utility drop. My parents house had a short circuit current around 5ka

4000 volt systems are typically fed from 100Kva and larger transformers of 4 to 10% impedance. Lets say a 10 megawatt transformer and 6% impedance, your short circuit current is 30 to 50,000 amps. Which my capacitor bank can do, for about 20 microseconds.

The highest ASCC I measured in our home for the 110 outlets was 0.39kA. 
https://www.eevblog.com/forum/testgear/trashy-meters-redux/msg4835948/#msg4835948
So you've cherry picked a lowball number as some argument against people discussing significant fault currents possible in residential/commercial installs. Pretty much exactly the same as the linked thread.

Why go on replying and arguing? Some installs have significant fault current available, some don't. But they're not specifically labelled or decorated differently (in most locations) so people need to treat them as worst case unless otherwise proven.
 

Online coppercone2

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Re: Interesting and sad case of electrical injury
« Reply #71 on: May 27, 2024, 02:50:43 am »
I'm sure your trying to make a point but it's lost on me.   I provided the data I collected from our home for a reference.   This was measured not calculated.   I've already explained there is no 4000V service feeding into our home.

 |O

The 5kA mentioned before would be between both legs of the phase, at 240V, at the origin of the installation. Whether you have 4kV at home or not isn't really relevant to his post.
This is all turning into a gigantic waste of time, but at least i was inspired to find out if the wires sticking up out of the ground on my neighbor's side of the road are live.

100 feet of 14 gauge wire (50 feet from your panel) is enough resistance that you can safely touch the wires together in front of your face and you will not be blown across the room by the expanding metal vapor cloud at 50,000 degrees kelvin!

here is a classic 480v clip


what is the current going on there? It looks like you combined about 40 or more high current stick welding arcs. That is gotta be like a few pounds of black powder going up in your face
« Last Edit: May 27, 2024, 02:53:39 am by coppercone2 »
 

Online coppercone2

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Re: Interesting and sad case of electrical injury
« Reply #72 on: May 27, 2024, 02:59:59 am »
does it do the jacobs ladder thing with multimeter leads?

Do the HV meters have like 40AWG meter leads for this purpose?
 

Offline joeqsmith

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Re: Interesting and sad case of electrical injury
« Reply #73 on: May 27, 2024, 03:02:43 am »
Why go on replying and arguing? Some installs have significant fault current available, some don't. But they're not specifically labelled or decorated differently (in most locations) so people need to treat them as worst case unless otherwise proven.

I wasn't aware of any arguments.  Rather I just provided a few measurements. 

Offline joeqsmith

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Re: Interesting and sad case of electrical injury
« Reply #74 on: May 27, 2024, 03:13:57 am »
What actually happens to a CAT-III 600V Fluke if you connect continuous 4kV to it?

i fully expect it to explode.

two cheap meters, a VC-99 and an older 2000 count meter survived 1999 volts on a slow rise time, but the 2000 count meter blew up when i reversed the polarity suddenly. -pretty sure i did not test the vc-99 the same way after the other one blew up.

I'm surprised you could apply 2kVDC into the VC-99 without damage.   Was in the DCV mode only? 

I've never tested a meter with enough energy to make one explode.   Worse case, I think a case once split open.   


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