120 volts AC vs 120 volts DC shock

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domnic

Senior Member
Occupation
Electrical Contractor
All things the same is their more danger in a 120 volt ac 60 hz than a 120 volt dc shock ?
 

mbrooke

Batteries Included
Location
United States
Occupation
Technician
All things the same is their more danger in a 120 volt ac 60 hz than a 120 volt dc shock ?

From what Ive been told, DC is safer than AC but only because DC is less likely to paralyze you to the source. If you get hit with DC, lets just say its the worst muscle cramp you can imagine. :happysad:
 

zog

Senior Member
Location
Charlotte, NC
AC for several reasons which have been discussed here many times but the key factor is that most LV shock deaths ocur from ventricular fibrilation which is caused by AC, not DC, in fact DC is used to stop defib.
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
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Electrical Engineer
Actually DC is used to stop fibrillation, and that process is called defib. :)
DC can also be used to restart normal rhythm from a flat line state.

LOL, good catch.

But it's worth pointing out, that takes place at nowhere near the levels we are discussing here.

Back to the 5 lb brick or hammer issue, BOTH are potentially lethal, so neither is safer. Safety is not really qualitative; something is either safe, or not safe. 120V, whether AC or DC, is not safe. I know your question technically was about "more danger", which I suppose might be qualitative, but the differences between those choices would only be by small degrees, which should not be considered relevant. The amendment to the brick / hammer statement I usually make is this:

The quality of suffering before death you experience from AC is likely slightly worse than the quality of suffering before death you experience from DC, but so far as we know, nobody has returned to provide feedback.

Cases in point: I have been shocked 480V AC and survived, but it fricking HURT like hell and I screamed and cursed for hours afterward. The only person I have ever seen killed by electricity died from touching a DC bus on a drive. He died quietly.
 

mirawho

Senior Member
Location
Sun Valley, CA
I have worked in a lot of different specialties in the electrical industry. My forte was service as I love figuring things out. But I also have worked in the electrical sign industry. I, for whatever reason, have likened the feel of getting shocked to a hammer. And the hammer gets bigger as the voltage goes up. I have had the displeasure to be hit off of a 15KV neon transformer. That is a big hammer. I knew this old guy named John that told me I didn't need a meter. This was many years ago. I asked him how he checked voltage. So we were out in the field one day and he said "I am going to answer your question". We were in a business that had 120/208V for utility loads and 277/480V for the lighting loads. He licked his finger and grabbed a wire and tapped it with his finger. He flinched a little and said, "This is 120v". At some other point, he did the same thing and snapped his hand back. He said, "This is 277v". I looked at him and told him I would stick to my meter.
 

jumper

Senior Member
I have worked in a lot of different specialties in the electrical industry. My forte was service as I love figuring things out. But I also have worked in the electrical sign industry. I, for whatever reason, have likened the feel of getting shocked to a hammer. And the hammer gets bigger as the voltage goes up. I have had the displeasure to be hit off of a 15KV neon transformer. That is a big hammer. I knew this old guy named John that told me I didn't need a meter. This was many years ago. I asked him how he checked voltage. So we were out in the field one day and he said "I am going to answer your question". We were in a business that had 120/208V for utility loads and 277/480V for the lighting loads. He licked his finger and grabbed a wire and tapped it with his finger. He flinched a little and said, "This is 120v". At some other point, he did the same thing and snapped his hand back. He said, "This is 277v". I looked at him and told him I would stick to my meter.

Would you believe that a similar method was shown in Electrical Handbook's of the 1920"s?

Sad, but true.
 

jeremysterling

Senior Member
Location
Austin, TX
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.
 

Bugman1400

Senior Member
Location
Charlotte, NC
I think DC is more dangerous since once it grabs hold of you, it doesn't let go. With AC, seems like you would have a better chance of releasing the wire or source when the potential crosses zero. However, AC is more prevalent in residential and commercial and is why more people are shocked by it.
 

zxfabb

Member
Location
LS
AC current could be more dangerous than DC under the same conditions. There is an in-depth analysis in IEC 60479.


"...For shock durations longer than the cardiac cycle, the threshold of fibrillation for d.c. is several times higher than for a.c. For shock durations shorter than 200 ms, the threshold of fibrillation is approximately the same as for a.c. measured in r.m.s. values."
 

Sahib

Senior Member
Location
India
please discuss how the shock of the earthed DC conductor is more or less dangerous than getting shocked by the neutral of AC. JK.
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.
 

kwired

Electron manager
Location
NE Nebraska
LOL, good catch.

But it's worth pointing out, that takes place at nowhere near the levels we are discussing here.

Back to the 5 lb brick or hammer issue, BOTH are potentially lethal, so neither is safer. Safety is not really qualitative; something is either safe, or not safe. 120V, whether AC or DC, is not safe. I know your question technically was about "more danger", which I suppose might be qualitative, but the differences between those choices would only be by small degrees, which should not be considered relevant. The amendment to the brick / hammer statement I usually make is this:

The quality of suffering before death you experience from AC is likely slightly worse than the quality of suffering before death you experience from DC, but so far as we know, nobody has returned to provide feedback.

Cases in point: I have been shocked 480V AC and survived, but it fricking HURT like hell and I screamed and cursed for hours afterward. The only person I have ever seen killed by electricity died from touching a DC bus on a drive. He died quietly.
One needs to also know the resistance or even impedance of the current path through the body. Apply voltage to one path in one instance and same voltage to two different input points on the body and you can get different results, plus there is a big difference from the path being between just two fingers on same hand as opposed to current passing through abdomen and through critical organs. If heart gets it you are often dead very quickly, but damage a liver or other organs you may have a slow and painful death.

Peak voltage of the 480 volts and the DC bus voltage of a drive (supplied with 480 volts anyway) are going to be about the same value of about 680 volts.
The AC voltage scenario will reach zero volts 120 times in one second if frequency is 60 Hz. RMS voltage of 480 is supposed to mean the effective voltage is approximately equal to 480 volts DC. I really don't know that means much though when it comes to asking which will hurt more or do more damage to a living being.

I have worked in a lot of different specialties in the electrical industry. My forte was service as I love figuring things out. But I also have worked in the electrical sign industry. I, for whatever reason, have likened the feel of getting shocked to a hammer. And the hammer gets bigger as the voltage goes up. I have had the displeasure to be hit off of a 15KV neon transformer. That is a big hammer. I knew this old guy named John that told me I didn't need a meter. This was many years ago. I asked him how he checked voltage. So we were out in the field one day and he said "I am going to answer your question". We were in a business that had 120/208V for utility loads and 277/480V for the lighting loads. He licked his finger and grabbed a wire and tapped it with his finger. He flinched a little and said, "This is 120v". At some other point, he did the same thing and snapped his hand back. He said, "This is 277v". I looked at him and told him I would stick to my meter.
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.

I think DC is more dangerous since once it grabs hold of you, it doesn't let go. With AC, seems like you would have a better chance of releasing the wire or source when the potential crosses zero. However, AC is more prevalent in residential and commercial and is why more people are shocked by it.
I kind of hit on the zero crossing in response above this one, but I don't know that it increases the chances by all that much. I do think a lower frequency possibly does result in more realistic response time to be able to pull away though. 50 and 60 Hertz is just too fast of a cycle time for human response, and is more luck than anything IMO if you would hit that cycle just right.
 

Fulthrotl

~Autocorrect is My Worst Enema.~
This guy was old as dirt. Maybe that was his reference manual.

well, that is most likely why it worked for him.

old people often are less conductive. drier skin, etc.
when i was an apprentice, i had an old journeyman who measured
voltage like that.... he told me to make sure i didn't do it that way
until i was as old as he was... said it'd knock the pee out of me if i
did.

i'm not that old yet. i still like my voltmeter. he was about 70 or so.
 

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
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.

I remember when you posted this a couple of years ago. It didn't make any sense then - Still doesn't now.

ice
 
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