Well David, I'm glad you liked it; but you didn't shoot any holes in it.
Transient analysis always applies...AC or DC...until you reach steady state. As a matter of fact, since the time constant for my assumed human body model (RC circuit 330pF and 5KOhm) is about 1.65uSec...when you first touch the circuit it will be very much like a DC response (think about it, the AC voltage has a period of 16mSec (in the US) so it won't change hardly at all during the first 5 time constants. (how much does AC line voltage change in 5 to 10usec? Not much at all) Most people assume that the initial transient conditions are over after about 5 time constants. I already did the math...at time zero, you will be subjected to 24mA of current, (assuming 120VAC and 5Kohm charging resistance through the body) which is well above the threshold of human sensation. Now, the current will only last a few time constants as your body capacitor gets up to charge. This would be a period of about 5 to 10 uSec. Can the human body feel such a phenomenon? Well, the human body can feel an ESD event which is even faster. (a period in the 100's of nanoseconds range). It would be about equivalent to setting your ESD gun to 120V and giving yourself a zap. I haven't worked up enough courage to go to my ESD gun yet...I think I'll let the numbers and inferences stand for themselves. Chris Maxwell Design Engineer Nettest From: David Heald [mailto:hea...@symbol.com] Sent: Monday, December 06, 2004 1:30 PM To: ken.ja...@emccompliance.com; emc-p...@ieee.org; Chris Maxwell Subject: RE: Is one-handed electrical shock possible? Most entertaining - particularly the last few posts :). Chris, I like your theory, and so I hate to shoot a hole in it... but this is AC, not DC (your model would be great for DC) - so we'd have a constant state of charge/discharge. Unless...the 60Hz is too slow to feel one handed, in which case the initial shock would also depend on the absolute value of the voltage at the time of contact. I'd like to see a current flow simulation run with AC including current at t=0 when the capacitor is connected to the AC source. You could get lucky and touch it when it was crossing zero and get no initial shock (?) or get progressively worse shocks as you reached peak voltage (woo-hoo!). I'm sure I could do the math and figure this out, but it's Monday. Best Regards, -Dave Heald While reading these posts, I was reminded of the time in college I was installing outlets at a campground and someone went down the hill to turn on the power (I was almost done). I apparently got distracted becasue a few minutes later I was still connecting wires and my hand started feeling funny. It took me a minute to realize what had changed and to adjust my grip on the outlet so that I was holding the top and bottom (not the sides) as I finished connecting the last wire. >>> "Chris Maxwell" <chris.maxw...@nettest.com> 12/06/04 12:07PM >>> Well Ken, I always admire a man who will put his tongue on the battery for the sake of scientific knowledge. I also admire a man willing to put up with a little electrolyte for the sake of canine companionship. There is only one living entity that is ALWAYS happy to see you come home...your dog :-) A couple of comments. According to "Electrical Engineering" by Carlson and Gisser; the threshold of sensation for the human body is about 1mA According to this same reference, the resistance through the human body varies from 500KOhm down to 1 KOhm depending upon whether the skin is wet or dry. You are probably correct about capacitance; and perhaps you have a good measurement of capacitance from your steady state measurements. If you go through the math, your body impedance with socks on does come out to about 10MOhm (according to your experiment, assuming the DMM has an internal impedance of 10MOhm). This impedance may be very much capacitive...and as a matter of fact, isn't that far from the human body capacitance values assumed for EN 1000-4-2 (330pF, I believe) I THINK THAT IT'S EUREKA TIME!!! Run with the human body model from EN 61000-4-2. Assume that the human body is a 330pF cap in-line with ...say 5K of resistance. If you perform a steady state calculation (calculating the impedance of the cap as 1/2piFC)...you'll get an AC impedance of 5KOhm + 8.038MOhm. If you divide 120VAC by this, you'll get micro amps...too little to feel. WE ALL FORGOT THE FIRST ASSUMPTION OF ELECTRICAL ENGINEERING...IMPEDANCE ASSUMES STEADY STATE. WHAT ABOUT THE INITIAL CONDITION? AT TIME ZERO, THE CAPACITOR LOOKS LIKE A SHORT CIRCUIT, LEAVING ONLY THE SERIES RESISTANCE In actuality, the one handed shock that you get is probably due to the in-rush current charging your body capacitance. The in-rush current may only last milliseconds; but that is probably long enough to feel it. If you really want to see the current, do a spice simulation with a 120VAC source. Put 330pF and 5Kohm in series with the source and run a ..TRAN analysis on it. Then look at the current over the initial few milliseconds...it should be more like 120VAC/5Kohm...which would be 24mA...plenty enough to feel. So, it seems that a shock is quite a matter of luck, depending upon the potential that your body happens to be charged to when you put your hand on that hot conductor. Insulated footwear, pillows, carpets...will lessen the steady state current; but you're still going to get the in-rush as your body charges up to line potential from whatever potential it was at. Further comments? Chris Maxwell Design Engineer Nettest This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to emc-p...@ieee.org Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Scott Douglas emcp...@ptcnh.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ________________________________________________________________________ This email has been scanned for computer viruses. ________________________________________________________________________ This email has been scanned for computer viruses. This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to emc-p...@ieee.org Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Scott Douglas emcp...@ptcnh.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
