Silly Q re electrocution

Must look at bad side of preceding post.

Wearing rubber gloves around hot metal is bad idea. Think about all of the chard leather gloves you've seen. If you had on rubber gloves the rubber would be melted into skin. Not a problem welding underwater. But rubber gloves can prevent shocks and wet leather gloves helps protect rubber melting when knee deep in mud or water. Would be nice if high temp silicon rubber gloves were available.

Bob Robinson wrote: If any part of the pipe is buried or in contact with the ground (they usually are), then you will automatically be grounding the return regardless of where you attach the clamp. So if you are in contact with the water (or wet ground) and you touch the stinger the current will have a path through your body. ^^^^^^^^^^^^^ Thanks, Bob. That answer dawned on my as I thought about it later. I wish I had an eraser.

In welding school (vo-tech school) there was a slight problem with the welders and tables at times. All of the welders were mounted to the "frames" of the welding booths (and all the booths were connected via angle iron, basically how everything was kept from falling over). We would typically use our stools to clamp our test plates together to tack them. So you'd move the ground to the stool of course. If for some reason you had your hand on the stool and touched the table you'd be pretty much stuck there for a short time. It was a good enough shock to wake you up, but you could break your hands free... it just took a lot of concentration to jerk them free. Everybody did it once, but it was good amusement (not safe, but some how funny at the time) when someone would do it more than once.

I'm not sure how this happened, but looking back on it, it just seems that can't be very good for the people, or even for the other welders.

-- Lynn "I have opposable thumbs, and I'm not scared to use em" Amick

Rod: Very possibly! Esp. how wet with sweat your arm is. Most ARChy's are 90 volts open circuit and that's what you'd feel. Ac or DC is irrelevant.

Rod: Most MIG's have _only_ 46 volts and yes you'll feel it too.

Mig you may feel it and remove your arm. Arc you may feel it and remove your arm. But good news! You have also sub conscious self preservation and you will react, move your arm, and LIVE! :):):)

Rod Ryker... It is reasoning and faith that bind truth.

least not as silly

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while - just never

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the bench top and

a 'wake up' call?

occasionally I

tip / wire while

"what if" type

I'm an electronics technologist, not a profesional welder, but I do know a thing or two about being shocked. First off, the most dangerous shocks are not the big ones, it's the medium ones that pass through your heart. It's something they call "the fatal current" which is, IIRC, about 50mA: yes, it's very little. This will set your heart fibrillating and you will die if it doesn't stop. Less current and you just swear. More current and you get burns but your heart keeps going. More current than that and you cook.

The moral of the story: be careful and use the one-hand rule. In welding, I suppose this means "don't hold your work with one hand while holding the welder with the other." Otherwise, any stray current would pass through your heart. If you only use one hand, or use both hands in the same place, then the current can't pass through your heart. Of course, if you're standing on some huge metal structure while welding, or in water, then this is pretty well moot. I only weld little stuff, on nice days ;)

David...

There's another issue with AC which makes it more dangerous.

Most voltages are specified in RMS terms -- this an average voltage (well not strictly true but close enough for this argument) so in the case of DC the RMS is the same as the actual voltage.

With AC however the RMS is less than the peak. Because AC is a sine-wave, there are times when there is *no* voltage and there are times when there is way more than the average (RMS).

So, 100V DC has a peak voltage of 100 -- because peak and average are the same.

But, 100VAC has apeak voltage of around 140V -- because 100 is only the average level and sometimes it's less (0V) sometimes it's more (140V).

Obviously 140V is a lot more than 100V so, in theory, you run a greater risk of electocution from AC than from DC -- if the RMS voltage is the same.

-- you can contact me via

A minor point. AC is more likely to cause problems. And with more current, your heart stops, but resumes its regular beating after the current stops.

That is what they are doing on the TV shows with those paddles. Stopping your heart so it can start up correctly.

Dan

More current and you get

Edison called AC the executioner's current and demonstrated by frying an elephant on stage.

Of course, the fact that he was pushing a DC power distribution scheme had absolutely NOTHING to do with this, right?

Ecnerwal wrote: Of course, the fact that he was pushing a DC power distribution scheme had absolutely NOTHING to do with this, right? ^^^^^^^^^^^^^ His opponents could just as well have fried an elephant on stage with DC. However, we elephant lovers object to such demonstrations.

If Edison had prevailed, our energy grid would not exist, and we would really have a crisis. Thank goodness for people like Steinmetz.

Lets not forget the guy who gave us all the original dynamo designs and distribution systems.

Nikola Tesla.

I still wonder what motors would be like if he had succeeded in getting

No one I know of would work in 3" of water unless it was a

I've also got a picture of a friend of mine about 20' out in a lake, wearing fishing waders, in water almost up to his waist, welding a lookout on a 36" steel pipe pile. His leads were strung out on the bottom of the lake, I told him he was lucky to not get a citation for illegal fishing : )

JTMcC.

Well, there are several DC components in the Grid, and those components have been touted for adding reliability to the areas they involve. i.e. The Hydro Power generated in Quebec is sent to NY by way of DC lines, then regenerated into DC at the user end. As I understand it, the Texas grid is also isolated by DC lines. If long distance transmission is done by DC, then reactive power does not need to be generated for those lines, and grid stability may be enhanced.

Stuart

The larger problem with AC is the frequency. And 60 hz used in the U.S. is worse than the 50 hz used elsewhere. The problem is that AC causes the heart to fibrillate. Twitch without the larger movements that pump blood. The same thing happens with heart attacks. And the cure is to use a pulse that causes the heart to stop and then allows it to start up with all the muscles in sync.

The higher peak voltage would cause higher peak currents, but to cause fibrillation the current only has to be about 30 ma. This is well below the amount that causes burning.

P.S. I enjoyed watching you in Junkyard Wars.

Dan

Hey it was a blast (quite literally :-). Mind you -- welding thin-guage stainless sheet into a pulsejet with a crappy MIG on build day meant a lot of TIG work was done on the safety day -- just so the whole thing didn't suddenly disassemble itself on starting ;-)

-- you can contact me via

Hum -

Having consulted with Texas Electric, Houston Light & Power, and a few more prior to merging - None had DC lines. I believe they had DC customers but rectified on-site.

I know that Houston Light & Power (might have the name rotated a bit) supplied electric power to the east coast during the first big blackout. Likely during the latter.

They eased back NASA and turned on the switch(es) to connect to the national grid.

El Paso wasn't on the Texas grid for years (if it is now ) since it supplied power to Mexico. THey might not do so now and might be on the Texas grid. The isolation was for political and govemental control of power generation and delivery. Texas wanted lines where they needed them not where some xxx person in D.C. said to put them - as is in California where the north-south lines are way undersized. They don't consider an emergency of general nature. Storms and pipeline issues force use.

The big DC users are steel companies and chemical plants. Most chemical plants generate their own. Or the large ones do - as DOW chemical does. MegaWatts of DC isn't handy to ship around so the power houses generate the 3 phase AC and rectification is done.

Martin

Rod: What is the (TYPICAL) AC Voltage and Current of High Frequency?

Rod Ryker... It is reasoning and faith that bind truth.

Yes, but I don't think the technology to do that was available in Edison's day, so AC won the battle because of the ease with which it could be transformed into a higher voltage for transmission.

My experience differs from yours. I contacted a 285 volt DC bus in a WP33 power supply (very stiff supply) and could not let go. I had to break a regulator tube (killing the supply) with the screwdriver in my other hand to get free.

Electricity causes the muscles to contract, period. If the contraction jerks you away from the power source, well and good, but if it clamps you tighter to it, tough luck.

Unfortunately, when you grab something with your hand, the muscle contaction causes the hand to clamp down tighter. If you brush it with the back of your hand, the contraction draws the hand away from the power source. So it depends on how you contact the live power source whether you'll be clamped to it or knocked free.

BTW nothing forces a muscle to violently extend. It can only contract or relax. Muscles operate in pairs across the joints so that the contraction of one will extend the other, and vice versa. So if, for example, the current passes through the biceps, your arm will contract. If it passes through the triceps, your arm will extend. But it is always the contraction of a muscle which causes the movement.

Gary