optoisolated power supply

John makes his USB cables out of multiple 0000 AWG cables.

Many years ago, when I worked as a CO tecnician at GTE, I came in one day at 4:00 and my boss hands me a box, and says to take them to the

1000 Palms CO, about 15 minutes away. I go grab my tools and look for the key to the truck, and he sees me and shouts "Why are you still here!"

I take the truck and the box, and as I drive up to this little office, out RUNS my second line supervisor! He grabs the box and runs back in. Now, having never seen my second line move faster than a saunter before, I became curious. I park the truck, and go inside.

There are a bunch of techs, at least a third line manager in there buzzing like angry hornets. Ask one of the techs what happened...

Seems a contractor was tightening the bolts on the buss bars over the batteries with an un-taped socket wrench, when he dropped it. It had fallen across both sides of the 48VDC bus. (buss bars were 1/2" x 4" copper, doubled) When it hit, there was a flash like lightining and it had knocked the entire office out of service.

What was in the box? Fuses for the power inverters. He had taken out every single one in the office, and they didn't have enough on hand to replace them all!

It was a good thing the guy was working on the buss from ABOVE!

They were sweeping up 'ball bearings' for months following that.

Charlie

That's because of the ringing voltage, which is higher, and AC, and dangerous.

Certain Eastern European countries used (use?) telephone ringing generators as "interrogation aids".

--
"For a successful technology, reality must take precedence 
over public relations, for nature cannot be fooled."
                                       (Richard Feynman)

BTDT.

--
"For a successful technology, reality must take precedence 
over public relations, for nature cannot be fooled."
                                       (Richard Feynman)

That

Answering both of you:

@JL This was about twenty years ago, they were not so extreme back then.

@FB This was NOT subscriber line interface equipment, is was switching systems and SONET. No ringing voltages, mostly 5 V and below digital signaling. But the labels were for the 48 volt supply.

BTW the arc voltage in welding is about 20 to 30 V and currents as little as 20 A. Of course the welding supply has a rather inductive output so that arc failures can result in sudden voltage jumps into 100s of volts.

?-)

He was lucky the batteries weren't venting hydrogen inside the building, or they would have had to start from scratch. Were those the special fast operating semiconductor fuses, that cost over $25 each?

Ohio Bell installed an early (SN < 20) ESS CO in Middletown Ohio. It went into a new addition, and they didn't notice that the electrical contractor had used zinc plated bolts in the overhead bus bars. The building contractor went cheap on the roof, so as the first heavy rain hit, the water ran through holes in the roof, and into the bus duct, followed by an explosion that blew out a lot of the cheap bolts. Sections of the bus bar had to be replaced, because it was too damaged to put back into service. Luckily, that was 'only' 10K out of 50K lines to that CO that were out of service for >18 hours.

But only once?

I don't think the fuses were that special, just large... 8-)

In the Palm Desert switch, they had cut over one exchange to a new #2EAX switch, while the rest was to remain on SxS till they were ready. Some customers, like Eisenhower Medical Center were put on special cutover blocks after the first major switch outage that lasted over an hour. For the first few month, those blocks got a lot of usage!

Charlie

That 10K ESS in Middletown was installed for Armco Steel (Now AK Steel) after they told Ohio Bell to either move them up the list, or they were taking their 10K block of numbers to a private exchange. The old CO was built of 1920's junk that had been removed from larger exchanges as the town grew. We had been told it would probably be another 20 years before we got the first ESS, because they had so many systems to scrap for parts to keep the mess running. There were times you had to wait a full minute to get a dial tone, or for a called phone to ring. People freaked when the public lines were updated. Dial tone on pickup, and the called number ringing as soon a dialing was complete. Also, they was a lot of noise & crosstalk on the old exchange. Sometimes you had to hang up and call back two or more times to get a usable connection. This was in the early '70s!

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it's just not a good idea to have anything connected to a living body at the time.

safety film

TWO reasons: (1) there is more than sufficient voltage to produce heart-stopping current for most people, and (2) there is more than sufficient current available to vaporize your stupid lip ring.

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safety film

** WARNING! DO NOT DISREGARD THIS WARNING! **

This might be the case, if the skin is punctured, especially in any medical equipment.

But for intact skin, it would be very hard to drive 50 mA through the heart, even if the skin is wet.

The EU LVD (Low Voltage Directive) is specified for AC 50-1000 V and DC 60-1500 V.

The IEC border line between ELV and LV (Extermely)Low Voltage is 50 Vac and 120 Vdc. However the 120 V is actually +/-60 V from grounded object, thus LVD and IEC agree quite well.

A decade ago, there was a great interest in increasing the voltage to

42 V (3 x "12 V" lead-acid battery). One reason was to remain within ELV even when charging (DC+ripple). Also above 50 V, it is harder to quench the arc.

On interesting data point: The 1890's street lights used arc voltages about 55 V.

Even a bank of 12 V batteries could cause severe burns.

Once was enough.

--
"For a successful technology, reality must take precedence 
over public relations, for nature cannot be fooled."
                                       (Richard Feynman)

That was kind of what I meant. :)

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At a ski area:

CAUTION: SIGN

--

John Larkin                  Highland Technology Inc
www.highlandtechnology.com   jlarkin at highlandtechnology dot com   

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME  analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

Robert Baer wrote Here in the US, cars used to use 6V batteries which were regarded as being very safe due to the low voltage. But there were many incidents of someone wearing a ring getting their hand in exactly the wrong place..losing the ring and finger at minimum. Then there was one case i personally know about where a person with rather low skin resistance "bought" that "its safe" BS and failed to use gloves for protection; the excess current thru the heart killed him; IF that had been AC,he might have had a chance.

----------------

Robert Baer wrote You are talking about 99.9% of the crowd. But this guy, like i said had very low skin resistance; a 1.5V penlight cell would shock him. A number of years later, i met someone with very high skin resistance

- hardly felt 120VAC.

----------------

Saying that a 6V BATTERY (itself) cannot shock is true.

For someone to say that a 6V automotive SYSTEM cannot shock is foolishness. People COMMONLY overlook inductive kick from a spark coil primary, relay coil or even generator field windings.

People are just not salty enough for 6V to matter. What is the range of salinity for the human body? Google hits report .09%, (8 oz salt) ocean is 3.5 %

Resistance/conductivity of a human body likely indicates salinity and any vulnerability to low voltage. Google searches for the resistance of a human body vary wildly from Megohms (typical textbook) to an absurd report of 100 Ohms.

I don't for a minute believe that it varies that much from person to person. I think those variations are reporting error, don't you, Robert?

This shows variations in dielectric parameters at 10-6,000 MHz. While not DC, it gives clues about salinity of various organs and body parts.

The standard for safety used to be 1 ma, has that changed?

Has there ever been a figure reported at which a person can even FEEL a current through skin?

It's easy to notice the electrochemical effect between two nearby points on your tongue, that you'd never notice through skin.

Is there a bottom limit for that?

The best I can do with wet, salty fingers squeezing alligator clips is about 60K.

--

John Larkin         Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro   acquisition and simulation

Then, it is NOT the 6V at that point, you STUPID FUCK.

G > For someone to say that a 6V automotive SYSTEM G > cannot shock is foolishness. =A0People COMMONLY G > overlook inductive kick from a spark coil primary, G > relay coil or even generator field windings.

J Shepard > =A0Then, it is NOT the 6V at that point,

Exactly.