More harmful shock from AC or DC?

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Pitt123

Senior Member
I have heard that a shock from DC voltage is more painful/harmful than one from AC of the same voltage magnitude. So for the same voltage potential will a shock from DC be more harmful and why?

I have heard maybe its due to the fact that AC corsses zero twice per cycle where as DC is constant and steady potential.

Is a taser gun AC or DC high voltage?
 

iwire

Moderator
Staff member
Location
Massachusetts
I have heard that a shock from DC voltage is more painful/harmful than one from AC of the same voltage magnitude. So for the same voltage potential will a shock from DC be more harmful and why?

I have heard maybe its due to the fact that AC corsses zero twice per cycle where as DC is constant and steady potential.
I will vote for the same all other conditions remaining constant.

I believe 120 volts AC is supposed to have the same energy as 120 volt DC. 120 volt AC does cross 0 but it also peaks well above 120 just as many times.
 

zog

Senior Member
Location
Charlotte, NC
The body reacts differently to each, AC is considered more dangerous for one key reason. Minimum let go levels, for AC it is around 15mA and for DC it is 75mA. Therefore the point where you lose muscle control, that causes the victims muscles to contract may casue the victim to become stuck on the energized part. Then duration becomes a factor, and it is a big factor.
 

ohmhead

Senior Member
Location
ORLANDO FLA
I know for a fact that 340 volts DC hurts like the dickens .
Well ill second that 480 volts dc hurts more than 480 volts ac the next time ill wait for the caps to discharge .

Its very short in time but it feels like one solid hour during shock!
 
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techntrek

Member
Location
MD
brian - ouch. I hope that was on one arm and not bilateral.

zog - I was taught that DC is more dangerous. DC locks your muscles so you can't let go, while AC pulses them giving you a chance to get thrown off. Probably just academic if it across your heart.
 

dereckbc

Moderator
Staff member
Location
Plano, TX
I will chime in with my two-cents.

DC tends to paralyze muscles and lock you in when contact is made. AC tend to make muscle expand and contract thus throwing you off the contact.
 

steve066

Senior Member
Well ill second that 480 volts dc hurts more than 480 volts ac the next time ill wait for the caps to discharge .

Its very short in time but it feels like one solid hour during shock!
Don't forget its the current that really shocks you. So it could just be the conditions for current flow were better when you came across the 480V DC. Different shoes or a different mositure level on your skin would probably make a much larger difference than DC or AC.

Steve
 

zog

Senior Member
Location
Charlotte, NC
zog - I was taught that DC is more dangerous. DC locks your muscles so you can't let go, while AC pulses them giving you a chance to get thrown off. .
DC tends to paralyze muscles and lock you in when contact is made. AC tend to make muscle expand and contract thus throwing you off the contact.
Old wives tale, you really think you can open your hand in the microsecond that current passes zero? Actaully AC cause muscle contraction and DC causes more of a cunvusoluary reaction.

This is all covered in IEC 479.
 
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Pitt123

Senior Member
Fortunately I have never experienced it, but I have heard people state that a shock from 120VDC was much more painful then an 120VAC shock.

What is it that a megger at 1000VDC will only cause a painful shock and wouldn't be the same as touching a normal 1000V DC service? Something to do with output impedance?
 

Hameedulla-Ekhlas

Senior Member
Location
AFG
Please read the below information.

Effect of duration of current: The magnitude of 50 Hz tolerable current is related to duration. According to tests reported by Dalziel, 99.5% of persons of 50kg weight can safely withstand the current given by equation.
I=0.116/ t sqr

where (I) is the rms value of body current in ampere and t is the time in seconds. If the weight of body is 70kg the equation for tolerable current is
I=0.157/t sqr

these equations are valid upto 0.03<t<3 seconds

Effect of frequency: The tolerable currents mentioned above for 50-60 Hz. It has been found that human body can tolerate about 5 times higher direct current. At high frequencies ( 3000-10000 Hz) still higher currents can be tolerated.
 

winnie

Senior Member
A megohmmeter is a current limited source. It might be 1000V open circuit, but the output voltage is designed to drop in order to maintain a certain maximum current. The jolt from a given megohmmeter may be current limited to a relatively safe value.

The maximum current can be quite high for some devices, and some high voltage test sets have lethal output. Also that limited current can still charge up cable and system capacitances to deliver a lethal jolt.

I've played with a little demo system made using a hand crank magneto and a current limiting circuit. The output voltage peaks at about 250V, but the output current is limited to below 1mA. You grab a pair of electrodes, turn a crank, and get shocked. Turn the crank faster and the shocks become slightly more intense and more frequent. I find the sensation really annoying but not in the least painful.

-Jon
 

brian john

Senior Member
Location
Leesburg, VA
Having the unfortunate luck of having been hit more than once by both AC and DC I would suggest your obituary may not note AC or DC just they fact you were electrocuted. AVOID getting shocked at all cost, obey all safety rules and regulations and wear proper PPE.
 

Pitt123

Senior Member
I guess with AC it could depend on where on the waveform the voltage is when you are shocked. If you touch it when it is nearing zero then this may not hurt as much as if you touched it when it was at a peak of 170V. With DC it is the same voltage no matter what.

A megohmmeter is a current limited source. It might be 1000V open circuit, but the output voltage is designed to drop in order to maintain a certain maximum current. The jolt from a given megohmmeter may be current limited to a relatively safe value.

The maximum current can be quite high for some devices, and some high voltage test sets have lethal output. Also that limited current can still charge up cable and system capacitances to deliver a lethal jolt.
How is the current limited? Is this by some sort of output impedance on the device?

So even though it is 1000V open circuit, when you put the leads on a cable (or body) the output voltage drops to some amount based on the current that it starts to output. For example if you put this 1000V device on a a cable, then current will start to flow based on output impedance of device, and cable circuit impedance, and this output current will cause a voltage drop across the device output impedance and thus drop the voltage to some lower value, lets say maybe 250V? So the cable or body would only have maybe 250V across it with leads connected?

If this is the case, why call it a 1000V megger as opposed to whatever value it drops to?

Why is DC voltage chosen for meggers? Is it to deal with the capacitive charging current from cables, that would flow with AC but is blocked with DC?
 

neity

Member
Two reasons AC is way worse.

1. Skin effect.

2. The human heart has a natural frequency of around 120 hz, which is pretty close to 60 harmonics wise. So yeah, reverse paddle effect can set in if it goes across your heart.
 

zog

Senior Member
Location
Charlotte, NC
Two reasons AC is way worse.

1. Skin effect.
And that makes AC worse how?

2. The human heart has a natural frequency of around 120 hz,
After running a mile maybe.

which is pretty close to 60 harmonics wise.
Why does that matter?

So yeah, reverse paddle effect can set in if it goes across your heart.
Reverse paddle effect?

THere are 2 primary reasons AC is worse, first the minimum let go current, which I explained earlier.

The other reason is Ventriciluar fibrilation, which will occur from AC and not from DC, and is the main direct cause of death from an electric shock.
 

drbond24

Senior Member
I have heard that a shock from DC voltage is more painful/harmful than one from AC of the same voltage magnitude. So for the same voltage potential will a shock from DC be more harmful and why?

I have heard maybe its due to the fact that AC corsses zero twice per cycle where as DC is constant and steady potential.

Is a taser gun AC or DC high voltage?
I'm pretty sure that the answer to this question could easily be obtained by calling your local penitentary and asking whether the electric chair is AC or DC. I believe that when they set out to kill somebody on purpose they use AC. :) That would make me think it is the more dangerous of the two.

Also, since a taser runs on batteries, it would have to be DC. I doubt they have internal inverters/converters (I can never remember which is which). I bought my wife a stun gun once, one of those you can hit a button and get a real nice arc across the two metal posts. It ran on a 9 V battery.
 
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