Post by thread:[OT] Muscle contraction. was: cats! -Reply

> Van: Kevin Allenzovic <spam_OUTMETakeThisOuTDOH.HEALTH.NSW.GOV.AU> > Aan: .....PICLISTKILLspam@spam@MITVMA.MIT.EDU > Onderwerp: Re: cats! -Reply > Datum: vrijdag 10 september 1999 7:02 > > This sounds a little impossible as AC would alternately contract and release your muscles forcing you to release it! This is one of the reasons we have AC supplied to our home and not DC, among ather obvious reasons. > Edison pushed for the use of AC by demonstrating on a horse. He'd fist hit it with AC and watch it bolt. When caught he'd again shcok it with DC killing it stone dead. No, you won't. Muscles are *NOT* current-direction sensitive ! AC (in a 50 or 60 Hz cycle) only means that your muscles are not contracted the whole time. just about 100-120 times a second. In the time between *you* would have to force your hand open & retreat. I wish you good luck with that. By the way: Your example with the horse does not prove that you will be "repelled" by a AC current, just that AC is not as deadly as DC. And that's because your (or the horses) hart will try to beat in a 100-120 Hz rithm. And that goes better than trying to beat when a DC current constantly pull's the hart-muscle together ... My 0.02 cents. Greetz, Rudy Wieser

All this out of my head - probably approximately correct but don't trust your life to it: Defibrillation (or more properly here, fibrillation) depends not only on current but also on duration. RCDs are designed to disconnect power within a critical period. I think it's within 50mS (which fortunately makes sense in the context of 50Hz (or higher) mains frequencies) and corresponds to a critical period during the heart's cycle. In fibrillation the normal voltage patterns of the heart are disturbed and while it may still oscillate it may subsequently do so in a mode which is not conducive to pumping blood. The television (and real life) "300, joules, clear, zap" routine is designed to polarise the muscle, clear all oscillation patterns and let the oscillator try and start clean again. (Master Reset). As you'll well appreciate if you've "field tested" one, an RCD does not stop you receiving a shock (the kick is not necessarily pleasant) but strictly limits the duration. RM From: G.C. <gary.cadmanKILLspamTIUK.TI.COM> >I think that these figures air on the side of caution. An RCD usually has a trip of 30mA all though you can get them in many sizes. >When I last looked at these type of figures I recall a statement that 30mA at 40V was sufficient to cause defiblaration. > >Jim Main wrote: >> >> I found the following pertinent info in a mag the other day, detailing >> whether or not you'd be able to let go a live source - it depends on the >> amount of current that's flowing through the muscle.. and gave the following {Quote hidden}>> rough guidelines.. >> >> 1mA - tingling feeling - no problem letting go >> >> 10mA - probably still able to let go >> >> 16mA - borderline able to let go >> >> 20mA - you're locked to it! >> >> Jim

Once again I must plead ignorance: Could someone please tell me what an RCD is? Thanks, Sean At 07:48 AM 9/14/99 +1200, you wrote: {Quote hidden}>All this out of my head - probably approximately correct but don't trust >your life to it: > >Defibrillation (or more properly here, fibrillation) depends not only on >current but also on duration. RCDs are designed to disconnect power within a >critical period. I think it's within 50mS (which fortunately makes sense in >the context of 50Hz (or higher) mains frequencies) and corresponds to a >critical period during the heart's cycle. In fibrillation the normal voltage >patterns of the heart are disturbed and while it may still oscillate it may >subsequently do so in a mode which is not conducive to pumping blood. The >television (and real life) "300, joules, clear, zap" routine is designed to >polarise the muscle, clear all oscillation patterns and let the oscillator >try and start clean again. (Master Reset). > >As you'll well appreciate if you've "field tested" one, an RCD does not stop >you receiving a shock (the kick is not necessarily pleasant) but strictly >limits the duration. > > > >RM > > > >From: G.C. <.....gary.cadmanKILLspam.....TIUK.TI.COM> > >>I think that these figures air on the side of caution. An RCD usually has a >trip of 30mA all though you can get them in many sizes. >>When I last looked at these type of figures I recall a statement that 30mA >at 40V was sufficient to cause defiblaration. >> >>Jim Main wrote: >>> >>> I found the following pertinent info in a mag the other day, detailing >>> whether or not you'd be able to let go a live source - it depends on the >>> amount of current that's flowing through the muscle.. and gave the >following >>> rough guidelines.. >>> >>> 1mA - tingling feeling - no problem letting go >>> >>> 10mA - probably still able to let go >>> >>> 16mA - borderline able to let go >>> >>> 20mA - you're locked to it! >>> >>> Jim > | | Sean Breheny | Amateur Radio Callsign: KA3YXM | Electrical Engineering Student \--------------=---------------- Save lives, please look at http://www.all.org Personal page: http://www.people.cornell.edu/pages/shb7 EraseMEshb7spam_OUTTakeThisOuTcornell.edu ICQ #: 3329174

Hi Richard, Thanks. Isn't this the same thing as a GFCI? I guess I have just never heard it called an RCD. I have never heard the term "MCB-type device" either. I assume "CB" stands for circuit breaker? Thanks, Sean At 11:43 AM 9/14/99 +1200, you wrote: >Residual current device (detector?) > >Basically an mcb type device that opens if the difference between phase & >neutral current exceeds a specified amount (5, 10 & 30mA are typical). The >difference current is assumed to be finding an alternative path via earth >and could then represent a hazard. > >Richard | | Sean Breheny | Amateur Radio Callsign: KA3YXM | Electrical Engineering Student \--------------=---------------- Save lives, please look at http://www.all.org Personal page: http://www.people.cornell.edu/pages/shb7 shb7spam_OUTcornell.edu ICQ #: 3329174

Ok, it all makes sense now, thanks. GFCI = Ground Fault Circuit Interrupter Sean At 12:28 PM 9/14/99 +1200, you wrote: {Quote hidden}>Yes - sorry - we get so used to our local jargon >MCG = miniature circuit breaker - as opposed to MCCB - moulded case circuit >breaker >I've also seen RCDs called "Earth Leakage Circuit Breakers" - elcbs > >Haven't come across GFCI but could well be the same thing > >Richard > | | Sean Breheny | Amateur Radio Callsign: KA3YXM | Electrical Engineering Student \--------------=---------------- Save lives, please look at http://www.all.org Personal page: http://www.people.cornell.edu/pages/shb7 @spam@shb7KILLspamcornell.edu ICQ #: 3329174

RCD = Residual Current Device. Measures difference between current in phase and neutral leads. Turns off power QUICKLY when the difference exceeds some pre-set value. A simple way to do this is to wind a few turns on a toroid from each leg so that the net currents sum to zero when they are balanced. When you get a return path to ground the go and return currents differ and the system shuts down. Speaking from experience (I think I was trying one out to see what it felt like :-)) you get a short sharp kick and then the power is gone. I don't recommend anyone tempting fate like this. If I MUST test something for liveness using my body (and the situations are few and far between) I make a closed fist and use the back of my hand - minimises risk of your muscle action causing you to grip the lead. You can still get a fatal shock this way if you are unlucky - YMMV. . RM From: Sean H. Breheny <KILLspamshb7KILLspamCORNELL.EDU> >Once again I must plead ignorance: Could someone please tell me what an RCD >is?

Thanks for all the replies. Perhaps this is a good time to bring up a question I posted a long while ago and never got a satisfactory answer: How do most people get shocked in general? In other words, what is the usual current path? Let's say that I grab a hot wire with one hand anf I am touching a grounded case with my other hand. Well,then its obvious. However, it seems to me that this would NOT occur in most cases. In most cases, only the hot lead would be contacting the body. In that case, the only available current path is into the floor. BUT, most floors are made of non-conducting materials. SO, how is the circuit completed? OR, would someone most likely not receive a shock in this case? In addition, you often hear of lots of people getting killed by dropping an electrical appliance into a bath tub. While I certainly recommend taking all precautions to prevent this,I don't understand why it is so often fatal. It seems to me that the obvious current path would be thru the water,bypassing the person completely. Unless the person was holding the appliance,in which case,again,the current path is obvious. However,this probably wouldn't be the case if the appliance just "fell" into the water,as the story often goes. Sean At 11:30 AM 9/14/99 +1200, you wrote: {Quote hidden}>RCD = Residual Current Device. > >Measures difference between current in phase and neutral leads. >Turns off power QUICKLY when the difference exceeds some pre-set value. >A simple way to do this is to wind a few turns on a toroid from each leg so >that the net currents sum to zero when they are balanced. > >When you get a return path to ground the go and return currents differ and >the system shuts down. Speaking from experience (I think I was trying one >out to see what it felt like :-)) you get a short sharp kick and then the >power is gone. > >I don't recommend anyone tempting fate like this. >If I MUST test something for liveness using my body (and the situations are >few and far between) I make a closed fist and use the back of my hand - >minimises risk of your muscle action causing you to grip the lead. You can >still get a fatal shock this way if you are unlucky - YMMV. > >. > >RM > >From: Sean H. Breheny <RemoveMEshb7TakeThisOuTCORNELL.EDU> >>Once again I must plead ignorance: Could someone please tell me what an RCD >>is? > | | Sean Breheny | Amateur Radio Callsign: KA3YXM | Electrical Engineering Student \--------------=---------------- Save lives, please look at http://www.all.org Personal page: http://www.people.cornell.edu/pages/shb7 spamBeGoneshb7spamBeGonecornell.edu ICQ #: 3329174

"Most technicians are shocked as Management had the workbenches built of metal, for extreme durability, and for "convenience" decided to ground the entire bench with 12AWG wire - That way there's always a ground handy when you need one." (My high school's benches were this way, we tended to stay well clear of HV stuff as if you were near the underside of the bench, your leg was GUARANTEED to be grounded or at best *near* ground, if you were wearing heavy long pants. NOT recommended, IMHO, to build benches this way!) I've seen techs working on live circuits, one habit for keeping you from grabbing a falling charged object is to cram the unused hand into a rear pants pocket, then make a fist, this tends to stop most people from whipping that hand out in time to catch that falling HV wire or whatever. Worst current paths are across the center of the chest - from left arm to right leg, etc. From arm to arm doesn't hit the heart AS badly as across the center of the chest, and of course neither's recommended <G> Mark Sean H. Breheny wrote: > > Thanks for all the replies. Perhaps this is a good time to bring up a > question I posted a long while ago and never got a satisfactory answer: How > do most people get shocked in general? In other words, what is the usual > current path? Let's say that I grab a hot wire with one hand anf I am > touching a grounded case with my other hand. Well,then its obvious. > <snipped>

Thanks for all the replies. Perhaps this is a good time to bring up a question I posted a long while ago and never got a satisfactory answer: How do most people get shocked in general? In other words, what is the usual current path? Let's say that I grab a hot wire with one hand and I am touching a grounded case with my other hand. Well, then its obvious. Back in 1955, Hurricane Hazel came through North Carolina. The eye of Hazel passed directly over the town I was living in. During the fist part of the storm, the neutral power line coming to our house came out of a screw connector at the house - thus we lost 110vac. There was about a 2 hour period of calm while the eye passed, so my Father decided to fix the problem his self. He knew that holding the neutral wire was not a problem - as long as he did not touch one of the hot wires. Up on a ladder, he was finding it hard to pull the neutral wire hard enough to get it into the connector. Suddenly he found himself with the neutral in one hand and a hot wire in the other. He could not let go. Fortunately, he had enough presence of mind to kick the ladder out from under him. The fall was enough to break his grip on the wires. He only suffered a broken foot (and probably some pride). By the time they returned from the hospital, the local power company had restored our power, since he was injured. I was only 4 at the time, and Hazel probably is my earliest vivid memory. My Father is 75 now and doing well. Here's hoping that Floyd (and Gert) miss NC - not that I willing wish ill-will on SC or Georgia! David V. Fansler (Burlington, NC) Network Administrator AutoCyte, Inc. 336-222-9707 Ext. 261 TakeThisOuTdfanslerEraseMEspam_OUTautocyte.com <RemoveMEdfanslerTakeThisOuTautocyte.com> Now Showing! http://www.mindspring.com/~dfansler <http://www.mindspring.com/~dfansler> Updated July 13, 1999 Thanks for all the replies. Perhaps this is a good time to bring up a question I posted a long while ago and never got a satisfactory answer: How do most people get shocked in general? In other words, what is the usual current path? Let's say that I grab a hot wire with one hand anf I am touching a grounded case with my other hand. Well,then its obvious.

On Tue, 14 Sep 1999 02:49:42 -0700 Mark Willis <mwillisEraseME.....FOXINTERNET.NET> writes: > "Most technicians are shocked as Management had the workbenches built > of > metal, for extreme durability, and for "convenience" decided to > ground > the entire bench with 12AWG wire - That way there's always a ground > handy when you need one." Any metal object that is routinely touched needs to be grounded. Otherwise it could become live and present a shock hazard by itself. It is bad practice to ground equipment to a bench. If the bench ground is defective, faulty equipment would make the bench live. It is best though to keep the number of conductive objects to a minimum where working with live equipment. >, this tends to stop most people from > whipping that hand out in time to catch that falling HV wire or > whatever. Get in the habit to not reach for *anything* that falls off of a workbench. Your brain isn't fast enough to evaluate whether it is safe to catch or not. Instead watch yourself and jump back if needed so it doesn't land on you. You may see a few expensive objects fall to the floor and break and wonder if you could have caught them. But that's a lot better than getting hurt by something that is too heavy, too hot, electrified, caustic, etc. to handle. The way to prevent things from falling to the floor is to not let them get close to the edge in the first place. ___________________________________________________________________ Get the Internet just the way you want it. Free software, free e-mail, and free Internet access for a month! Try Juno Web: dl.http://www.juno.com/dynoget/tagj.

>Get in the habit to not reach for *anything* that falls off of a >workbench. Your brain isn't fast enough to evaluate whether it is safe I have a friend who instinctively caught an Xacto knife that was falling. Stuck through his palm. Fortunately it missed the ligaments. Andy ================================================================== Eternity is only a heartbeat away - are you ready? Ask me how! ------------------------------------------------------------------ EraseMEandyrc-hydros.com http://www.rc-hydros.com - Race Boats RemoveMEandyEraseMEEraseMEmontanadesign.com http://www.montanadesign.com - Electronics ==================================================================

Sean H. Breheny wrote: > Once again I must plead ignorance: Could someone please tell me what > an RCD is? Residual Current Device(?). Core Balance Relay - type circuit breaker. Old Earth Leakage Circuit Breakers (ELCB) monitored current in the earth line - no good if you contact the plumbing, so pretty useless and rather unreliable when we had one, though it did trip when the 'fridge defroster shorted out (it wouldn't reset - had to be turfed!). Core Balance Relay describes it all, both lines (Active and Neutral) pass (once or more) through a toroidal transformer, a third winding on which, with or without electronic amplification, operates the trip relay within 50 ms. Rated at 30 mA domestic, 10 mA medical. Common problem relates to using only one to "protect" a whole household. Fridges are commonly excepted as (well-grounded and cord rarely open to damage) consequences in terms of food spoilage can be very nasty. *Proper* usage is one per power circuit. Most commonly tripped by (bugs in) dishwasher, other problem was with moisture build-up in unused clothes-dryer heater. I'm very surprised the washing machine hasn't tripped it yet! -- Cheers, Paul B.

Hi Paul, Thanks for the explanation. When you said that you were surprised that the washing machine never tripped it,are you talking about the washer in my house? If so, AFAIK, RCDs are NOT standard in US homes. In fact, I have never seen such breakers (that I recognized,anyway) on a whole circuit,only on individual low-current outlets (usually in bathrooms) and integrated into certain appliances (usually hair dryers). Do homes in OZ usually have one on each circuit? Sean On Tue, 14 Sep 1999, Paul B. Webster VK2BZC wrote: {Quote hidden}> Sean H. Breheny wrote: > > > Once again I must plead ignorance: Could someone please tell me what > > an RCD is? > > Residual Current Device(?). Core Balance Relay - type circuit > breaker. > > Old Earth Leakage Circuit Breakers (ELCB) monitored current in the > earth line - no good if you contact the plumbing, so pretty useless and > rather unreliable when we had one, though it did trip when the 'fridge > defroster shorted out (it wouldn't reset - had to be turfed!). > > Core Balance Relay describes it all, both lines (Active and Neutral) > pass (once or more) through a toroidal transformer, a third winding on > which, with or without electronic amplification, operates the trip relay > within 50 ms. Rated at 30 mA domestic, 10 mA medical. > > Common problem relates to using only one to "protect" a whole > household. Fridges are commonly excepted as (well-grounded and cord > rarely open to damage) consequences in terms of food spoilage can be > very nasty. *Proper* usage is one per power circuit. > > Most commonly tripped by (bugs in) dishwasher, other problem was with > moisture build-up in unused clothes-dryer heater. I'm very surprised > the washing machine hasn't tripped it yet! > -- > Cheers, > Paul B. >

Sean Breheny wrote: > When you said that you were surprised that the washing machine never > tripped it,are you talking about the washer in my house? No, mine. > Do homes in OZ usually have one on each circuit? Unsure on exact practice. Rules say must have RCD on power circuits in domestic use, not business(!). As common practice is still to have only two, maybe three power circuits per house, it would be sensible to have two as previously mentioned. Of course I have as I may have mentioned, no less that seven power circuits including two dedicated for computers and amateur radio, initially fitted on three RCDs, but to be extended to at least five. (Problem: RCDs use two slots; so where 2 circuits were fitted with 1 RCD, had RCD and 2 current breakers, total 4 slots, replacement with 2 RCDs which include current break no problem. 3 circuits on one RCD took 5 slots, can't be readily upgraded!) -- Cheers, Paul B.