mivey
Senior Member
Do rabbit ears make a good ground?
which one is more dangerous ac source or dc source
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T.M.Haja Sahib
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I do not remember he gave any.
IMO the first rabbit died due to magnitude of the applied D.C voltage and the second rabbit died, despite withstanding the current from the DC source,due to change in polarity i.e due to a change in DC voltage wave form.A clue to this phenomenon is provided in the paper
'A review of hazards associated with exposure to low voltages' by Dr. Marom Bikson
Department of Biomedical Engineering, City College of New York of the City University of New York,in the para
'Tissue heating depends on the RMS values of the current and little or not-at-all on its
waveform/frequency (e.g. the RMS value of a sinusoid is independent of frequency). However, for electric stimulation (shocks) the waveform of the current can have a profound influence on current efficacy (Bikson et al. 2004). AC (e.g. 60 Hz sinusoidal) is considered more likely to induce hazardous electric shocks than dc current (Camps et al. 1976; Reilly 1998). Dalziel and Lee (1969) found 10-400 Hz currents most effective in inducing involuntary hand muscle contraction. DiMaio and DiMaio (2001) considered 39-150 Hz the most lethal. Kugelberg (1976) found frequencies between 12-60 Hz most effective in inducing fibrillation of the human heart. The two competing factors relating to stimulation frequency efficacy are: 1) as electrical excitation occurs during the rising or falling phase of the current flow, increasing frequency increase the amount of potential excitations per time (e.g.involuntary muscle contractions); 2) excitable cell membranes act as low-pass filters (Bikson et al.2004), higher frequencies are thus less effective. Unless otherwise stated the results reviewed here refer to 50/60 Hz sinusoidal waveforms (as are used in power distribution systems)'
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mivey
Senior Member
I think the first rabbit died because he was the weaker of the two. Continuous shock was bound to kill the second rabbit sooner or later, polarity change or not.
Where does it discuss the DC polarity?
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T.M.Haja Sahib
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Both rabbits were fit as fiddle.
The second rabbit suffered instantaneous death due to polarity change.......
It did not explicitly state it because,perhaps the two scientists did not know about the work of each other.
mivey
Senior Member
Then how is it providing a clue to what the other scientist was doing? Can you please explain what you are talking about?
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T.M.Haja Sahib
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mivey
Senior Member
OK. Meaning the changing polarity we have with the AC voltage wave is more dangerous that the steady voltage we get from typical DC.
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- Massachusetts
DC has a wave?
K8MHZ
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- Electrician
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- Massachusetts
10/4
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
We also have to remember the body can act as a capacitor which will change the way current flows when analyzing AC verses DC, more like a low pass filter, higher frequency's will tend to cause heat as the capacitance will tend to be more of a short to the current passing through the body.
Once you get above 500hz you tend to feel more of a burning sensation then a shock.
Once you get above 500hz you tend to feel more of a burning sensation then a shock.
iceworm
Curmudgeon still using printed IEEE Color Books
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I don't have any evidence about 500HZ, but I have a statistical sample of one that says in the 1700Mhz to 2400Mhz range it is definitely a burning feeling. Hurt for more than a year as I recall.
ice
Aystole is no more or less a dire condition, in both cases the heat is not beating. I do agree AC is more dangerous, VF(ventricular fibrillation) caused by electrocution may be reversed easier than Asystole. This is highly dependent on two factors, early CPR and, in the case of VF early defibrillation. With VF, the cardiac tissue has not completely depolarized, thus just a shock, that "resets" the heart may return spontaneous circulation. With aystole, sustained CPR may oxygenate the cardiac muscle cell enough to get things going.
So, make sure the guy you are working with can do adequate CPR, seriously.
Also, with my highly unscientific poll, of my personal experience, aystole has a higher negative medical outcome percentage than VF, regardless of the cause.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
I would think that would still be considered AC because of the flywheel effect of the coil fed from points or electronically
RF burns can be dangerous and very painful as it burns the inside of you, but the frequency's you referenced are in the microwave range and you don't even have to make contact with the conductor at those frequency's as you can receive burns just being close to it if there is enough energy, in the HF range 1-30mhz range it can still hurt, and still burns inside you. and it is a long lasting experience.
broadgage
Senior Member
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- London, England
There seems to be a general view among electricians that DC is more dangerous as regards electric shock.
DC is undoubtedly more dangerous as a cause of fire, DC will continue to arc across a small gap such as a defective connection, great heat is generated thus which can not only ignite combustible materials, but can burn holes in metalwork.
AC will not normally continue to arc, unless in especially unllucky circumstances.
Under UK regulations DC is considered to be more dangerous, but of course regulations do not allways reflect reality.
A voltage of up to 25 volts AC or 120 volts DC is considered in the UK to be less dangerous.
Some think that it should be the other way round !
DC is undoubtedly more dangerous as a cause of fire, DC will continue to arc across a small gap such as a defective connection, great heat is generated thus which can not only ignite combustible materials, but can burn holes in metalwork.
AC will not normally continue to arc, unless in especially unllucky circumstances.
Under UK regulations DC is considered to be more dangerous, but of course regulations do not allways reflect reality.
A voltage of up to 25 volts AC or 120 volts DC is considered in the UK to be less dangerous.
Some think that it should be the other way round !
K8MHZ
Senior Member
- Occupation
- Electrician
That's an interesting assertion. It's been a while since I have had my scope connected to the primary side of an ignition coil, but I don't recall seeing the wave ever drop below the zero line. But then, that's not what I was looking for. The book has examples of patterns that show bouncing points, bad capacitors, etc. (Yeah, points. The scope is that old) along with what a normal pattern looks like. Next time I am downstairs I'll go take a look.
iaov
Senior Member
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- Rhinelander WI
I asked a new helper the other day what was the most important thing that he new about electricity. He replied "It will kill you. " I told him he gets an "A" for the week!!
mivey
Senior Member
Next week he will learn it can kill him also.
PS: learn from teaching, not experience as that would be a bad thing.
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- San Francisco Bay Area, CA, USA
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Next week he will learn it can kill him also.
PS: learn from teaching, not experience as that would be a bad thing.
That last part sounds like a corollary of the old saying I heard on day one of my apprenticeship:
"There are old electricians, and there are careless electricians, but there are no old careless electricians."
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
No wait, I got it wrong. The more I thought about it the clearer it became...
"There are old electricians, and there are bold electricians, but there are no old bold electricians."
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