Freaky Amazing DMM?!

bud-- wrote in news:e5611cbd-ea3c-4de1-88dc- snipped-for-privacy@v18g2000pro.googlegroups.com:

He whom I killfiled long ago is persistently reminding me why I killfiled him. And he's wrong. And when he gets a fine red-gold-black coating across his face sometime he'll know how wrong he is.

That's about the size of it. It only happened to me once, and it wasn't even that big, it was just the ends of some 100A cables burning back from a contact, lasting about half of a second. I'm a civilian, but that's about as close I know to the experience of being shot at by live rounds at close range. It's a deeply shocking experience, it makes reactions poor, instead of reversing the move that caused the event, a stunned brain only registers a failure and retries the SAME move! Never mine autonomous seizure in case of electric shock, neural shock DOES this without the added woe of electrical contact. It took a real effort of will to override my body's false assumptions and prevent a third blast, and it taught me something of what soldiers have to learn to do in combat, so they respond correctly. I'm lucky I remained standing and didn't shit myself, and equally lucky I have good eyesight remaining after being flashed at and coated with enough copper to make my eyes sting for days. If the whole cable had gone up it would have probably slammed me against the wall and broken my spine and fractured my skull. As it was the sound was like the most brutal and guttural swearing, it carries an emotional weight as well as just being very loud. I know this is just the brain trying to rationalise its experience, but that's my point, even in mild form like that one, arc flash at many tens of amps is a STRONG experience.

I had a lesser one that did nothing to me, but still shows the power. It was two fully charged industrial deep cycle 105AH 12V lead acid batteries in parallel. I managed to let one wire drift and gently pass its end across the side of another one, and there was no resistance, just a complete destruction as one passed through the space occupied by the other. In this case the arc was just weak enough that some sputtering occured instead of total plasmafication, but there was a lot less copper bits than were eaten out of the cable, so even there, most turned to separate molecules of copper oxide and vanished in the ambient airflow.

I wrote this because I'm annoyed with the claim and counterclaim, flame and counterflame. It's MY experience, and no-one, whatever they say, is going to be able to contradict it. Hopefully no-one's going to try.

I know that a high resistance input can be interpreted across a known load, but I also know enough not to argue against assertions that meters made to do this are both safer and more convenient. I just use a Fluke meter and some load I have to use if needed, but I don't have to do this every day. If I did, I'd make it pay for the meters that do it as I'd need it done.

Reply to
Lostgallifreyan
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How surprising. You still have no idea what arc flash is.

The thread is about "low voltage" - below 600V (particularly 480V for the US).

The quote above is about "low voltage" as is the source article.

You are still stupid. And do not know the limits of what you know. And not willing to learn.

-- bud---

Reply to
bud--

So does a screwdriver against the case, and to a buss bar, but I won't do it.

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There are two kinds of people on this earth:
The crazy, and the insane.
The first sign of insanity is denying that you\'re crazy.
Reply to
Michael A. Terrell

??????? Don't be stupid.

Reply to
Arlowe

How NOT surprising that you are still making retarded assessments based on ZERO facts.

You do not know a goddamned thing about what I may or may not be familiar with.

You are a goddamned retard. You should f*ck off and die... Hopefully as the result of a huge copper vapor arc flash. Bwuahahahahaha!

Spattered... spattered... his brain's been splattered, spillin' all over...

Goddamned google groups retards.

Reply to
Archimedes' Lever

Do you means stupid, like a row of question marks is?

I have always hated little gang boy retarded punks in my news groups.

You cannot gauge stupidity from your depths of stupidity, you stupid twit. Yes, you are deep in the barrel.

Reply to
Archimedes' Lever

Poxy hell. Step back Mike. I am not ready to believe you are that damn ignorant about arc flash hazards yet.

Reply to
JosephKK

You really don't get what Bud's talking about.

Arc flash while working in 'low voltage' switchgear (600V or less) can be deadly. And most electricians *do* use a handheld meter working in such switchgear. There is no need for high-voltage probes there. Bud's not talking about high voltage overhead transmission lines.

The very high fault currents available in such load centers can/do cause vaporization of copper. (yes, *vaporization*, where the copper actually changes to the gaseous state). Such load centers may have a feeder that won't trip below 1000 amps or higher. A 'high impedance' fault such as a sustained arc that draws several hundred amps at 600V will not trip the feeder and so it will continue to arc for quite some time. All that power concentrated in the confines of a load control center will vaporize a good deal of the conductor.

Arc flash protection includes specially rated face shields that can absorb the energy of a condensing gas cloud of copper without melting. Ordinary plastic face shields are not allowed in such work as the heat from the plasma gas cloud will just melt them onto your face. Similar precautions are needed for the arc flash suit material worn.

daestrom

Reply to
daestrom

I don't want your job. You're the expert at stupid.

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There are two kinds of people on this earth:
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The first sign of insanity is denying that you\'re crazy.
Reply to
Michael A. Terrell

I'm not. I was pointing out that it can cause the same damage. Anything to create the initial plasma will cause the same thing, including fuses with too low of an extinguishing voltage, or an idiot sparky who uses damaged test leads. I always though it was odd that electronics techs use well insulted probes, while sparkies use crap probes with a lot of exposed metal. Let one of his test lamps short and he can see the fireball that erupts, if he lives long enough. He talks about not understanding dangerous test methods, yet he uses one himself.

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There are two kinds of people on this earth:
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The first sign of insanity is denying that you\'re crazy.
Reply to
Michael A. Terrell

Actually it does cause false voltage readings even in circuits with no "loose nuts". You can connect the meter to a point in the circuit that is open somewhere, perhaps because of an open switch contact, and you get false voltage readings that can range from 10V to close to line voltage due to stray pickup of the wires. It causes electricians to sometimes misdiagnose problems, and it causes confusion. I often demonstrate this to my training classes so that they are aware of it.

This is an unavoidable and unfortunate side effect of high impedance digital meters. You need to understand it when you use them so that you can question and investigate readings that don't make sense.

Analog meters don't have this problem, but they are disappearing because the analog circuits can not meet the necessary safety standards.

Ben Miller

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Benjamin D Miller, PE
www.bmillerengineering.com
Reply to
Ben Miller

You mean that cheap analog VOM had low impedance inputs. There were millions of VTVM and FET input analog meters with a 10 Megaohm input impedance in use over the years, and a lot are still in use.

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There are two kinds of people on this earth:
The crazy, and the insane.
The first sign of insanity is denying that you\'re crazy.
Reply to
Michael A. Terrell

Of course not. The "loose nut" is the one interpreting the measurements.

Right. The typical sparky is clueless. This fact has been demonstrated here endlessly.

It certainly may be if you're clueless.

"Analog" has nothing to do with it.

Reply to
krw

Those are great on a lab bench, however very few were ever used for industrial power measurements. FET inputs are not notoriously rugged, although they could be used if desired. It is difficult to run an extension cord for a VTVM out on a factory floor, not to mention the smoke that can escape when you apply a grounded test lead on a power system measurement, assuming that you survive to talk about it :-(

You will not find very many analog meters with an IEC CAT rating, with good reason. The typical analog industrial meters such as the Amprobe RS series or the Simpson 260 series have resistor networks on the inputs, and very likely don't have the requisite creep and clearance distances in their construction. There are also problems with the Ohms circuits. One of the IEC requirements is that you can safely apply maximum rated voltage (ie. 600 or

1000 volts for example) to the meter inputs with the range and mode switches set to any setting. The meter doesn't need to continue working, just fail safely or do nothing. Many meters have fuses for the amp ranges, but analog ohms circuits can fail catastrophically if high voltages are applied to them. The manufacturers just can not justify the redesign of those meters to meet the safety standards.

Ben Miller

--
Benjamin D Miller, PE
www.bmillerengineering.com
Reply to
Ben Miller

AND they worked fine for the purpose being discussed and still do.

Reply to
Archimedes' Lever

Bwuahahahahaha! I just love made up statistics.

Your true colors are showing.

I know you are smart, but this bolstering of your OPINION bullshit is just that and nothing more.

Reply to
Archimedes' Lever

No bolstering of anything and no statistics. This is based on personal observation.. I have seen electricians of all ages using many types of meters, from wiggy's to amprobes to Radio Shack digitals to high end Flukes. I have NEVER seen any of them carrying around a VTVM and an extension cord to power it! It is completely wrong for industrial measurements, not to mention unsafe. Explain, for example, how you would measure line-line on a

480 volt three-phase system, with a VTVM that has a grounded probe (yeah, I know, a three-prong adapter and a piece of cardboard to isolate the meter enclosure.)

I won't say the same thing about FET input meters, as there might be some used. I just have not seen any. Since they are battery powered, they at least have isolated leads.

We have electricians on this group. Let's see what they say.

Ben Miller

--
Benjamin D Miller, PE
www.bmillerengineering.com
Reply to
Ben Miller

Some VTVM had a built in battery for portable use. They were rare, but they existed. They used subminiature tubes with a 1.5 or 3 volt filament like those in early hearing aids.

The 260 is a dinosaur, over price instrument in today's work environment. Even if it was modified and certified, it would be sold to a niche market and not worth the engineering costs.

The early FET input analog meters I've used would die if their was a tiny spark when probing. If they had a small choke on the input to filter the RF, they were fine, but it would void the certification.

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There are two kinds of people on this earth:
The crazy, and the insane.
The first sign of insanity is denying that you\'re crazy.
Reply to
Michael A. Terrell

NOBODY said a goddamned thing about an AC powered device. Other than YOU.

Reply to
Archimedes' Lever

I have seen VTVMs powered by old B+ batteries, as in a 63 Volt source.

Just to depose what I know was going to be your "You don't even know what a VTVM is!" CRAP, before it even starts.

Reply to
Archimedes' Lever

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