120 volts AC vs 120 volts DC shock

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Besoeker

Besoeker

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UK
Sahib said:
In an experiment, two rabbits were connected in series across a DC 120V power source. The moment supply was turned on, the rabbit connected to the positive terminal died and the other rabbit remained alive. When the supply polarity changed, it also died. So it seems that which polarity DC conductor is earthed decides the safety in your case.
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Got a link to the experiments?
 
Besoeker

Besoeker

Senior Member
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G

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Consulting Electrical Engineer - Photovoltaic Systems
This is a bit like asking whether you would be more dead if you were hit by a bus or by a semi.
 
J

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
jeremysterling said:
Now that we're clear on which current is more dangerous, can we please discuss how the shock of the earthed DC conductor is more or less dangerous than getting shocked by the neutral of AC. JK.
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An AC neutral is typically a grounded conductor, so I'll assume that's what you meant.

Typically there is no risk of getting a shock from either a grounded DC conductor or AC conductor if that wiring is still properly terminated to a grounded terminal or bus. That is, of course, as long as you are not also touching the ungrounded conductor at the same time. :slaphead: You have to complete a circuit to get shock. The most likely way of doing this is by touching an exposed ungrounded conductor while standing on the ground or touching grounded parts. It's the same with AC or DC.

In a PV solar system you also have to watch out for the fact that a normally grounded conductor may be no longer grounded if there is a ground-fault detection fuse that has blown. Thus you could become a path and get a shock if you touch an exposed 'grounded' conductor, especially if also touching grounded racking or raceways that are faulted to the ungrounded conductor. (That fault is likely to exist, since it's the reason the fuse would blow.) Systems are supposed to be labeled with this warning but it's something you should know by heart if servicing PV systems.
 
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mirawho

Senior Member
Location
Sun Valley, CA
kwired said:
What is the impedance of the 15KV neon transformer compared to a 15KV power transformer, that neon transformer will have current limitations, and they may be low enough even to effect the low current passing through a human body during such an incident. On the farms the electric fence chargers also can run into the 10's of thousands of volts, but they have a very high impedance as well which limits the current to a non lethal level, but not all critters are immune to it. Cattle are thick skinned and may need 10kV to get enough of a shock to be effective yet a bird happens to come in contact with that line (and a grounded object) and they are instantly dead, seen it happen a few times, or at least seen the dead birds laying next to the line.
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They use a high leakage inductance. The current ranges from 30mA to 300mA. I was hit off of a 60mA.
 
R

Ragin Cajun

Senior Member
Location
Upstate S.C.
I have been "bit" by everything up through 115KV (via a defective hot stick in the rain!).

Getting hit by my fence charger was also nasty, but it was one of those "pulse" chargers. It sure stung!

RC
 
zog

zog

Senior Member
Location
Charlotte, NC
tom baker said:
And thats why AC is more dangerous.
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Actually no, they have the same net energy, you can argue that logic backwards by saying AC also crosses zero. The only effect voltage directly has on shock severity is skin effect where higher voltages actually do less damage (for the same current) than lower voltages. Take a look at buswork used in HV substations, hollow tubes because that is the only part of the conductor used due to skin effect, same would happen to a person which is the trick to those high voltage daredevil acts you see people do.
 
J

jeremysterling

Senior Member
Location
Austin, TX
Sahib said:
In an experiment, two rabbits were connected in series across a DC 120V power source. The moment supply was turned on, the rabbit connected to the positive terminal died and the other rabbit remained alive. When the supply polarity changed, it also died. So it seems that which polarity DC conductor is earthed decides the safety in your case.
Click to expand...

I'm not clear with your description of the experiment. You state the polarity was reversed. Then you conclude that the earthed pole decides safety. Reversing polarity in a circuit is not the same as changing the earthed pole. You made a leap bigger than the rabbit's.

jaggedben said:
Typically there is no risk of getting a shock from either a grounded DC conductor or AC conductor if that wiring is still properly terminated to a grounded terminal or bus.
Click to expand...
Tell that to the rabbit. JK.
 
S

sbrehler

Member
Having read these posts, I am wondering why it is that most people don't understand that that the Cardinal Rule of electricity is, "it isn't the voltage that kills you, it is the current!" Yes, a difference of AC-vs.- DC may boil down to the fact that you may not be able to let go of the conductor, but if you have a path that leads through your heart you will probably die either way. I have been shocked by both 120 V and, in the case of my automobile's ignition wires, somewhere in the range of 13KV. Both hurt, but I survived.

Just last week, I reached into my tool pouch and grabbed my Kline "demolition" screwdriver...the one with the shaft that goes all the way through the handle to work on an outlet (yes, live), and got the shock of my life (I know, very dumb mistake). All I can say is that the handle contacted the palm of my hand, and not my finger tips, and hence I got a poke from 120V that I will not forget! It wasn't like the "touch it with your finger" kind of poke. It went from on from my right hand through to my left and had me shaken for quite a few minutes. All the while thinking, " is my hear going to stop?"......It didn't. :)

So, as far as which is more dangerous...well, sit in a puddle of water, or a damp crawlspace, and then decide.

Bottom line, current kills, not voltage!

Just my $5 worth...adjusted for inflation.:D
 
Sahib

Sahib

Senior Member
Location
India
jeremysterling said:
I'm not clear with your description of the experiment. You state the polarity was reversed. Then you conclude that the earthed pole decides safety. Reversing polarity in a circuit is not the same as changing the earthed pole. You made a leap bigger than the rabbit's.
Click to expand...
Well, assuring that I shall present the supportive reference of rabbit experiment (a scan copy) soon, consider positive polarity of a DC supply is earthed and its earth resistance is considerable. If any grounded person then touches negative polarity, the injury he may receive may be lesser compared to the opposite case per the rabbit experiment.
 
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ActionDave

ActionDave

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Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
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Licensed Electrician
sbrehler said:
Bottom line, current kills, not voltage!

Just my $5 worth...adjusted for inflation.:D
Click to expand...
My $5 worth, adjusted for inflation of course, ........ I have had my hands on at least 200A worth of current hooking up batteries and breakers on cell sites and lived to type today, important thing is the voltage was 24V.

Sure it only takes a tiny amount of current to stop your heart but you need enough kick behind it to get it there.
 
kwired

kwired

Electron manager
Location
NE Nebraska
sbrehler said:
Having read these posts, I am wondering why it is that most people don't understand that that the Cardinal Rule of electricity is, "it isn't the voltage that kills you, it is the current!" Yes, a difference of AC-vs.- DC may boil down to the fact that you may not be able to let go of the conductor, but if you have a path that leads through your heart you will probably die either way. I have been shocked by both 120 V and, in the case of my automobile's ignition wires, somewhere in the range of 13KV. Both hurt, but I survived.

Just last week, I reached into my tool pouch and grabbed my Kline "demolition" screwdriver...the one with the shaft that goes all the way through the handle to work on an outlet (yes, live), and got the shock of my life (I know, very dumb mistake). All I can say is that the handle contacted the palm of my hand, and not my finger tips, and hence I got a poke from 120V that I will not forget! It wasn't like the "touch it with your finger" kind of poke. It went from on from my right hand through to my left and had me shaken for quite a few minutes. All the while thinking, " is my hear going to stop?"......It didn't. :)



So, as far as which is more dangerous...well, sit in a puddle of water, or a damp crawlspace, and then decide.

Bottom line, current kills, not voltage!

Just my $5 worth...adjusted for inflation.:D
Click to expand...
Possibly a much better chance of some vital organ damage thought when current enters one hand and leaves the other hand, compared to entering one hand and leaving via the leg on same side of body. Some people dies days later after a shock incident because of internal injuries they were not aware of and thought they were alright. Going to a hospital ASAP and having some vital signs monitored for a relatively short time can indicate potential problems that result in sudden illness a few days later and they can treat those problems before they become serious.

ActionDave said:
My $5 worth, adjusted for inflation of course, ........ I have had my hands on at least 200A worth of current hooking up batteries and breakers on cell sites and lived to type today, important thing is the voltage was 24V.

Sure it only takes a tiny amount of current to stop your heart but you need enough kick behind it to get it there.
Click to expand...
You also were not in the path of 200 amps of current, the voltage needs to be very high to be able to push 200 amps through an average human body. Even if you put yourself in series with that 200 amp load @ 24volts - your body resistance is so much higher then that of the load that practically no current is flowing - need really low scale measuring devices to read what little is flowing.
 
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