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If my voltage applied is 170v and my resistor is 1M Ohm then my current is what? Only 0.00017 what unit is this measurement?

Thread starter #1
I have a question. Since my resistance measured from my left thumb tip to my right thumb tip is 5M Ohms to 15M Ohms depending how tightly I grip the meter then my body is a high resistor.

I am wondering since my resistance is so high if I calculate with Ohms law the voltage out my wall socket is 116v - 170v peak, Lets say 170v to be on the safe side. I will say my body resistance is at 1M Ohm only to be on the safe side of things. I will calculate 170v/1M Ohm = 0.00017. Is this right? If I touch live AC wires then only 0.00017 will pass through my body? How do I say 0.00017 , it isn't even 1mA so what is this measurement in amps? (I'm not just going to go around touching live wires, but I am curious).

I see some peoples resistances measured is from only 100k Ohm - 350k Ohm max range and wonder why mine is also so high. If I measure resistance on my tongue tip it is 2 - 6M Ohms range also depending how tightly I probe. My meter is accurate up to 0.02% on resistors and it could be the resistors that are off and not my meter in this range, as I am not sure. If the current is only 0.00017 then would I even feel that. Seems safe to the touch or are all my calculations completely wrong? What am I missing? Why do people get electrocuted? If I calculate normal resistance as 100k Ohm then applied over the same 170v peak line it is 0.0017 which isn't even 2mA right?

Can someone please explain this to me because I am not understanding this I think.
 

JimB

Super Moderator
Most Helpful Member
#2
(I'm not just going to go around touching live wires, but I am curious).
Yes, please don't do that.
Otherwise you will quickly find out that the human body does not behave like a simple resistor, and it will hurt!
You cannot predict the current which will flow through a human body when a high voltage is applied, based on resistance measurements done using a low voltage.

OK, back to the theoreticals.

If you connect a 1M Ohm resistor to a 117v supply, you are correct in calculating that 0.00017 amps will flow.

You could convert this to milli-amps by multiplying by 1000.
This will give you 0.117mA.

Or, you could go a bit further and multiply the 0.00017 by 1000000 to get the answer as 117uA (micro amps).

JimB
 

JonSea

Well-Known Member
#3
I = V/R where

I = current in AMPS
V = volts
R = resistance in Ohms

I = V/R = 170/1,000,000 = 0.00017 Amps

0.00017 Amps × 1000mA/Amp = 0.17mA

The Fatal Current talks about the effect of current on the human body at various levels. 0.17mA is a very low current, but as this reference stresses, resistance across skin can vary greatly. Contact pressure, skin condition (i.e., dry or wet) and location make a huge difference. They claim the resistance from one ear to the other is only around 200 Ohms.

Also keep in mind that current passage through muscles tends to make them contact. That light touch on a wire may turn into a hard pinch that you can't release. If you grab a wire in each hand, that current will go across your heart, and you won't be around to post about your experiment.

I can assure you - coming into contract with 120VAC can really hurt!
 

unclejed613

Well-Known Member
#5
that ohmmeter measurement you got sounds like it's pretty high, maybe you measured on dry skin, or on callouses on your fingertips. if you do the same measurement with wet skin, you'll more likely get somewhere in the neighborhood of 10k ohms or even less. every insulator has a breakdown voltage of so many volts per millimeter, which is a threshold at which it begins conducting. air, for instance has a breakdown voltage of about 3kv/mm (it varies a bit depending on humidity and air pressure). i would expect that dry skin has a much lower breakdown voltage than air has, because there remains a small amount of moisture, plus electrolytes (like salt) in solution within the cells. my best guess would be about 100V/mm, and a layer of dry skin or even callouses are going to be less than 1mm thick. it may easily withstand the approximately 2V on the meter probes, but not 120V.
 
Thread starter #6
Ok thanks for the replies. I measured on dry skin and even over 2M Ohm on tip of wet tongue. Also know my measurements are correct because I have measured values on a lot of different resistors from 1 Ohm up to 10M Ohm range. I also measured my kids and theirs is normal range 100 - 300k Ohm from one hand to the other except one of my kids measured over 3M Ohm on her hands and is a lot higher resistance like my skin.

Am I correct that saying 0.17mA is same as 17mA ? That is same number of measurement wrote two different ways? Or is it only wrote as 0.17mA? Meaning not even 1mA.

Thanks again guys for responding.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
#7
As others have said, that resistance value seems pretty high - however, I presume it was measured with a digital meter?, and these tend to give far higer skin readings than old analogue ones.

But it's important to understand that skin resistance varies MASSIVELY, based on a wide range of factors - you can't calculate what current might flow from mains by measuring resistance at a low voltage (and in the case of a digital meter a VERY low voltage).

If your meter is supposedly accurate to 0.02% then presumably you paid more for it than you would for a luxury sports car?, meters aren't that accurate, and there's no point in them been so.
 

gophert

Well-Known Member
Most Helpful Member
#9
No, completely wrong how can 0.17 be the same as 17 when you're using the same units? - it's obviously 100 times smaller.
100 times smaller?

0.17 mA x 100 = 17.

So 100 times smaller would be 0.17 - 17 = -16.83

I don't think you meant that but I that is what you said.

I think the phrase you were looking for is "one one-hundredth"

 

dknguyen

Well-Known Member
Most Helpful Member
#10
100 times smaller?

0.17 mA x 100 = 17.

So 100 times smaller would be 0.17 - 17 = -16.83

I don't think you meant that but I that is what you said.

I think the phrase you were looking for is "one one-hundredth"

The statement was (16.83/17.00) * 100 = 99% correct which is...good enough lol
 
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Thread starter #11
Ok thanks for helping me understand better.

I have 3 meters for comparison and a "Resistor Kit" from 0 - 10M Ohm range and they all test accurate. 100 Ohm reads 100 Ohm on both and 10 M Ohm reads 10.09M Ohm at highest and 10.04M Ohm on another and 10.07M Ohm on my 'Part Testing' meter. I would say they are all very accurate and measure up to 10M Ohm range just fine compared to my resistors and 0.05% off isn't going to make my measurements off by much compared to any form of measurements.

I will also tell you why I think my resistances are so much higher than normal. I use a treatment through my hands that sends 15v DC through my left hand while soaked in water up through to my right hand for 10min each week then reverse polarity and send opposite direction for 10 mins, totally 20 minutes of treatment in a device like: iontoderma but was built by myself and not their specific machine.

The first week of treatment I electrocuted my hands every day for a duration of 20 minutes. I use to feel the current and now I don't even feel it any more. So it is my best guess that my body has developed a stronger resistance now to the electricity. Iontoderma was used to treat a condition I was born with called hyperhidrosis.

Now I am cured from it and my hands are soft smooth and feel normal. The only difference I have noticed is that by measuring my resistance on skin, it has increased. Anywhere I measure it and even on tip of tongue is over 2M Ohm and usually over 12M Ohm range when I probe my skin. If I do a test under my skin tissue I will update and let you know the readings and result but don't plan on jabbing these under my skin any time soon but will test if I get a cut or two.

I also wonder if there could be any negative effects from this by continuing the treatment because not much research has been done with this machine and the effects on humans are still kind of unknown from prolonged use.

Anyways, thanks again for the responses everyone!
 

Tony Stewart

Well-Known Member
Most Helpful Member
#12
I have a tendency to sweat easily and can tolerate cold temps well perhaps from growing up in Manitoba (Manit'scoldhere) but never have I heard of this condition before.

I have calibrated my fingers often, and it is very dependent on pressure and voltage potential. Since dry fingers can yield uA currents with low voltage the skin thickness has a low dielectric breakdown and thus the resistance may abruptly drop from Meg to kilo-ohm levels quickly if the breakdown voltage is exceeded. This threshold depends on how many layers of subcutaneous skin breakdown with a threshold that depends on ionic contaminants such as salt and moisture. Air is typically 1kV/mm from a sharp point so if the insulation layer is less than this, there is severe risk of electrocution going from one hand to the other thru the heart muscle with line voltage. You would want to limit the current with 1 or more series Resistors for safety.

The tongue being a wet surface can easily detect the voltage of a 9V battery as the current flow is much higher from lower resistance and even lower if it reaches ionic layers below the surface. A strong 9V battery will sting like bee with pressure, a weak battery will not due to higher internal resistance..

Acupuncture methods tend to use inductive spikes at some repetition rate to inject pulses for various alternative healing methods.
 
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gophert

Well-Known Member
Most Helpful Member
#16
What I said was that 0.17 is 100 times smaller than 17, 17/100=0.17
I know what you said but your math does not align with your words.

Your words say "100 TIMES less". Yet you DIVIDE by 100 when you do the math. It doesn't make sense.

What happens when you say 2 times less than 17? I assume that is 8.5 by your calculation.
What happens when you say a half times less than 17? Is that also 8.5? I couldn't imagine it means 34 - or does it? If it means 8.5, then your mathematical proof must also show that 2 = 0.5.

PS: "one percent of" or "one one-hundredth" are much clearer ways to explain the comparison between 0.17 and 17.
 
#19
...
If I measure resistance on my tongue tip it is 2 - 6M Ohms range also depending how tightly I probe.
...
Listen to message #2. If you want an example of how reading ohms across your body is not accurate, put a standard 9V battery across your tongue. Based on your measurements and assumptions, you should not feel anything, but you do. Meters are not a reliable method to measure human body tissue resistance...
 

Tony Stewart

Well-Known Member
Most Helpful Member
#20
Listen to message #2. If you want an example of how reading ohms across your body is not accurate, put a standard 9V battery across your tongue. Based on your measurements and assumptions, you should not feel anything, but you do. Meters are not a reliable method to measure human body tissue resistance...
Your tongue is moist and will measure around 30k depending on contact area for 2 probes. If your finger is dry it can measure 100x times bigger or 3M for both thus half that each , so between finger and tongue will be 30k/2 + 3M/2 = 1.53M. But never try that with line voltage as it could be fatal. The most I have tried was -48V on my tongue very quickly and very small area to see why my modem wasn't working in the early '90s. crazy.

Long term effects for electroshock therapy have been used for psychotic issues in the past and acupuncture treatment to stimulate the body's immune system. The currents they use to stop a heart in surgery due to the invasive moist direct connection are uA levels and similar to what pacemakers use. However extremely dry outer skin can be many orders of magnitude higher resistance. However due to small skin thickness the risk to abrupt drop in resistance and rise in current is a major risk, so external current limiting e.g. 1M should be considered. If you read about line safety hazards, will find examples of spontaneous human death by combustion but it is very graphic. {arc flash}
 
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