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I'm trying to make my workshop safer but I can't understand how electrocution happens.

For example, one hand is touching to live wire and neutral wire is not touched. If I know right, current flows from live wire to my body and to ground wire or earth but dry human hand's resistance is between 10-40k ohm so even my feet is touching directly to ground current is between 5.5-22mA and fatal dose is 30mA but how people get electrocuted from live wire without touching to ground or neutral wire?

Also can I measure resistance between live wire (or my hand) and ground? So I can get more accurate results.

I think I wasn't clear about my question : In my scenario neutral wire is insulated so current "have to" flow into ground , I understand my body's resistance not enough but floor or house have resistance too .

I made a small test for measuring resistance between my house and ground and I got three results :

1)One probe of multimeter connected to ground wire other probe connected to floor (I tried radiator too same result) multimeter showed more than 20M ohm resistance

2)One probe of multimeter connected to ground wire other probe connected my hand (feet touching to floor) multimeter showed 5M ohm resistance

3)One probe of multimeter connected to ground wire other probe connected to my left hand and my right hand touching to ground wire ,multimeter showed 200k ohm resistance

So only third scenario allows 1-2mA current other scenarios seem safe . if you see any mistakes in my tests please notify me so I can learn the truth. Also when I making these tests I used special extension plug which only conducts ground wire other wires isolated from plug

Mordecai
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    *"Maybe most of people who got electrocuted is touching live wire and neutral wire at same time"* I can tell you from experience that this statement isn't a correct assumption. I've been electrocuted by 440V and it was because somebody wired something wrong in both cases. All I did was touch the metal casing of the equipment and got zapped both times. Luckily all I got was a single phase... – Ron Beyer Sep 01 '19 at 20:21
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    Stop playing - you might get it wrong... – Solar Mike Sep 01 '19 at 20:22
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    Stop treating 30mA as a hard barrier between fatal and not fatal. That's like saying a bullet is only fatal when it becomes larger than X caliber. – DKNguyen Sep 01 '19 at 20:25
  • I've been electrocuted from 220v too , when I was plugging lamp to wall outlet one of my fingers touched to live but I don't understand why it happened .In my mind circuit is not closed because it needs ground or neutral which I didn't touch – Mordecai Sep 01 '19 at 20:26
  • Probably because it went in one part of your finger and back out the other part, essentially you were a "parallel" circuit. If you were grounded, it would have travelled that path. But think about it, you can put something between one live wire and another, as long as it eventually reaches ground it completes the circuit. – Ron Beyer Sep 01 '19 at 20:27
  • If you measured resistance with a DMM, then keep in mind that DMM has 9V battery and when you connect your body to HV, then the resistance is getting lower. – Marko Buršič Sep 01 '19 at 20:31
  • @Ron beyer So you're saying current flowed in my finger to neutral ? – Mordecai Sep 01 '19 at 20:33
  • Kind of yes, lets say you lay your finger along a conductor. The electricity may go in near your finger tip and out nearer the knuckle back into the circuit. It eventually flows to neutral but you are just creating a parallel flow, kind of like hooking a resistor up parallel to a line. Something may flow through it but the majority still goes through the main conductor. – Ron Beyer Sep 01 '19 at 20:39
  • So if I understand right , for example my finger's resistance is 1k so 220mA current flows and my body's resistance is 10k so parallel circuit type 22mA current flow through my body and that's why I got shocked ? – Mordecai Sep 01 '19 at 20:43
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    I'm voting to close this question as off-topic because it is not about making workshop safer rather than speculating under what conditions you can get an eletrical shock. The latter is NOT E.E. – Huisman Sep 01 '19 at 21:34
  • @Huisman if I can identify the reasons which causing electrocution , I can avoid them and if I can avoid the electrocution it makes my workshop safer . You can't solve a problem without know what's causing the problem – Mordecai Sep 01 '19 at 22:48
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    @RonBeyer If you lived to talk about it then you were **not** electrocuted. You were just **shocked**. The definition of electrocution requires that you were **killed** by an electric shock. – Elliot Alderson Sep 01 '19 at 22:48
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    Electrocution/shock flowchart: Did you feel something No, no shock and no electrocution. Did you feel something, yes? are you dead? yes then you may have been electrocuted. Did you feel something, yes? did you survive? yes? then you were shocked (not electrocuted). There are not very many people in the world who can truthfully type the phrase "I was electrocuted". – user57037 Sep 01 '19 at 23:10
  • *How does electrocution (fatal) happen?* When somebody starts playing around with 'would this current kill me?' questions, and pushing the envelope. Fit GFCIs, keep things insulated, don't work on live stuff, keep your workshop dry, keep it tidy, replace any broken plugs/leads rather than repair with tape, and the question will hardly ever arise. – Neil_UK Sep 02 '19 at 05:29
  • In the united states, the National Electric Code is over 1000 pages. Your country probably has a similar code. The way people avoid getting electrocuted is by doing things as specified in the electric code. Maybe some countries have lax codes or lax enforcement. If so, study the codes from other countries that are reasonably safe. In general you get electrocuted when current flows through you. There are a lot of ways for that to happen, but usually they involve higher voltages (over 50 volts) or very unusual circumstances. – user57037 Sep 02 '19 at 06:23
  • All assumptions and tests are invalid as well as criteria. When skin ionizes from high V your skin can conduct orders of magnitude more current or lower R !! – Tony Stewart EE75 Sep 02 '19 at 13:58

2 Answers2

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The amount of current needed to kill is not some exact number. It is around 20mA. One person will die at 20mA, another lives despite more current flowing through his body.

Body resistance is not fixed, either. On a cool, dry day where you don't sweat your skin resistance will be higher than on a muggy day with the sweat pouring off your body.

220VAC can push enough current through your body and through the ground (the literal ground or floor under your feet) to kill you.

Never work on live 220V circuits.

Have all 220V circuits in a closed, insulated or grounded container when they are operating.

Have a ground fault interrupter installed in the house wiring or outlet you use when experimenting.

Your "theory" that people are only killed by touching live and neutral is wrong. If you rely on live to ground being safe, then it will kill you one day - and before that, you will experience painful shocks from the current that isn't quite high enough to kill you.

The ground wire in your house is connected to the ground (literal ground made of dirt outside your house.)

The ground wire is connected to the neutral wire in your house.

Your house and the floor are connected to the ground, and thus to the neutral.

Grabbing the live wire while standing in your house is therefore the same as touching live and neutral.

JRE
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  • I have differential relay in my workshop don't worry . Everyone saying body resistance changes but I'm asking how the current flow through ground or neutral wire ? Like everyone knows plastic boots prevent electrocution but floor have high resistance too , why it reacts differently ? – Mordecai Sep 01 '19 at 20:36
  • Wood and concrete aren't rubber. – JRE Sep 01 '19 at 20:39
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    Besides simple resistance, there is also a capacitor effect between your feet and the floor. Even if you have an insulator (rubber or plastic) between your feet and the floor, AC can still make it's way through you. – JRE Sep 01 '19 at 20:41
  • But its so little to be fatal ? – Mordecai Sep 01 '19 at 20:44
  • but why house doesn't have any resistance ? You're saying like house is made of copper – Mordecai Sep 01 '19 at 20:45
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    i read a post earlier from someone that said, that he has learned that a differential relay does not always prevent a shock – jsotola Sep 01 '19 at 21:17
  • @jsotola Differential relays can't work with insulated transformers , I went to electric company to ask this question and engineer said they connect three phase neutrals in Star connection and connect the middle part to ground with 5 ohm resistance – Mordecai Sep 01 '19 at 23:13
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    @Mordecai: Houses **have** resistance. How much they have varies. If you depend on it having **enough** resistance then some day you will touch a live wire in a house where the resistance is lower than you expect - and it will kill you. So, act like houses are made of copper. It is safer. – JRE Sep 02 '19 at 05:38
  • @JRE Thanks for comment , now I understand why people treating house as conductive because it's safer to assume every bush as bear because one day bush could be bear – Mordecai Sep 02 '19 at 06:13
  • Also, 220VAC is the RMS value. It is 660 volts peak to peak. That makes quite a difference, too. – JRE Sep 02 '19 at 06:16
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First, dry hand resistance is 10-40k ohms, maybe. But it varies from person to person, and when you're stressed, it goes down.

People generally find it very stressful to be holding onto a live electrical wire, unable to let go because it's shocking the @#$% out of them. Think about that for a moment...

If it's hot and you're working anyway, you'll be sweaty. Sweat is mostly salt water. Think about that for a moment...

In addition, that 30mA figure is what is immediately fatal -- getting a lesser shock may not kill you immediately, but it can damage your heart. You may not care now, but future-you may not be happy with present-you, and your future-spouse will be really unhappy with present-you.

Yes, you can survive a few shocks -- more at 120V North American voltages than the 220V of most of the rest of the world, but even 220V. The last time I got zapped (with 120V), I felt it in my chest for most of the afternoon. I certainly thought about that, and how pissed my wife will be with me if I happen to keel over 20 years too early from congestive heart failure brought on by playing with live wires in my youth.

Read up on proper lab procedures, and follow them. Most really bad accidents happen because of a concatenation of errors. You don't stay safe by looking at the first possible error and saying "that won't hurt me". You stay safe by looking at the rare possibilities and keeping them from happening.

Because the first time you grab 600V because you were treating it as 60V? It'll be a once-in-a-lifetime event. Literally, and tragically (and your spouse will be pissed).

TimWescott
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  • Often it is because the shock time does not hit the heart cycle at the right, or wrong, time so you survive... – Solar Mike Sep 01 '19 at 20:29
  • But circuit supposed to be closed so for example my feet is touching to wooden floor , current has to flow through my body and floor ? I remember in the university my teacher said voltage isn't important , if you're touching metal surface even 5V can be deadly – Mordecai Sep 01 '19 at 20:29
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    @Mordecai Don't exaggerate, the 5v can't hurt nobody. What is below 48VDC or 34 VAC is safe. – Marko Buršič Sep 01 '19 at 20:33
  • @MarkoBuršič 20mA across the heart at the right time in the heart cycle can stop the heart... not something you want to test to prove it... – Solar Mike Sep 01 '19 at 20:41
  • @SolarMike I don't need to test it, they already did it. 48VDC is a safe voltage, there is no way you can die, that's why is safe. – Marko Buršič Sep 01 '19 at 20:56
  • Also since you mentioned it : I read something about why AC more dangerous than DC and If I understand it right ; you can't survive from 100-300v AC but you can survive from 1kV or higher because 1-50 mA current is similar to brain signals and it interrupt heart muscles but high current (or voltage) won't interrupt the heart muscles but it only burns tissue . is it correct ?(I'm assuming not burning to death but heart attack) – Mordecai Sep 01 '19 at 21:11
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    @Mordecai I personally know somebody who was electrocuted to death on 4160V, I know 2 people who died (but were revived) working on 1KV transformers. I've been shocked more times than I like to admit on 120V and never died. I don't know where you're getting that information but it is dangerously incorrect. – Ron Beyer Sep 01 '19 at 21:13
  • If I remember right one of my friend said that . He survived 33kv electrocution (transformer explosion) one of his arm burn to crisp but still survived. I need to talk with electric company's engineer again , like still I don't understand how current flow through my house to ground that easily – Mordecai Sep 01 '19 at 21:16
  • Somewhere on YouTube there is a video of a suicidal guy climbing a pylon carrying at least 100kV. He touches it, disppears in a ball of fire, falls about 25m - and unluckily for him, survives. – Dirk Bruere Sep 02 '19 at 07:19