# Thread: When does DC voltage become dangerous?

1. ## When does DC voltage become dangerous?

Ok, theoretically in the right place you could probably be killed with 1ma @ 1v. More realistically speaking, when does DC voltage become dangerous to touch with your bare hands? 36v? 48? 75? How high does it need to be before you should be afraid of it like 120v sockets?

Just curious...

2. ## Re: When does DC voltage become dangerous?

It varies, you usually start feeling it at about 50Volts, which also is about the limit in safety regulations. And as with any powersource, not the Voltage is dangerous but the current.
I may check this in more detail when I'm back at home.

3. ## Re: When does DC voltage become dangerous?

IF you drop down 1 metre you could die
if you drop down 25 you could survive !!

same goes for voltage ,,don't be afraid for sockets They hurt but, normaly you wont die unless you put some wet steel rods in them and grab them with your hands for a long time !! ,,,, has somthing to do with how easy the current goes through You.

4. ## Re: When does DC voltage become dangerous?

also you can touch 10000v electrical fenses , but they only hurt like **** and won't kill you same reason: not enough current !!

5. ## Re: When does DC voltage become dangerous?

Probably not going to find an exact number people can agree on, but I'd say 60+ VDC.

6. ## Re: When does DC voltage become dangerous?

36-48 is where you might start feeling it. It depends on varying conditions. 50v is where you start to have to aboe3y different wiring standards per the National Electric Code.

You must remeber that dc is much more hazardous than ac of the same voltage. Dc will sustain an arc at much lower levels than ac. If you get shocked by dc you will likely not let go of what you touch. Ac will trow you away.

7. ## Re: When does DC voltage become dangerous?

It depends how sensitive you are, whether you have sweaty hands, and so on. I can certainly feel a tingle from 24 V, and in the wrong circumstances 12 V could be enough to kill you.

If you always assume electricity is dangerous you won't go far wrong.

8. ## Re: When does DC voltage become dangerous?

Originally Posted by jhellwig
You must remeber that dc is much more hazardous than ac of the same voltage. Dc will sustain an arc at much lower levels than ac. If you get shocked by dc you will likely not let go of what you touch. Ac will trow you away.
Conventional wisdom in electrical engineering is exactly the opposite. The most common form of electrocution death is from stopping the heart. 60 Hz AC is much more likely to cause heart stoppage than DC current of the same voltage.

AC voltage is quite good at causing muscle contractions and causing you to "clamp on" to an exposed wire as well.

9. ## Re: When does DC voltage become dangerous?

The position of the shock, and distance between entry and exit points is critical. A voltage of 60V per cm across your body will cause tissue damage. If the entry and exit points are somewhere like your leg, you can survive even the frighteningly high voltages from lightning. If the voltage goes across your heart, even 100VDC could be fatal and stop it.

10. ## Re: When does DC voltage become dangerous?

Here's some info from the CDC.

http://www.cdc.gov/niosh/docs/98-131/overview.html

It lists around 16 mA as a current level where you may not be able to let go.

Around 20 mA can paralyze your respiratory muscles and stop breathing.

100 mA can cause ventricular fibrillation and stop the heart. This is particularly dangerous because even if you get disconnected from the current, your heart won't necessarily restart.

11. ## Re: When does DC voltage become dangerous?

Good info... just a word of caution though... the figures you've quoted are at ~600VAC 60Hz though, not DC.

12. ## Re: When does DC voltage become dangerous?

I heard somewhere that low DC voltages that you may not notice can do electrolysis damage to cells. Supposedly, a person was killed while working on a vehicle with a 24 volt battery and some how manged to get pinned with part of his body in contact with one of the terminals and another to the body (ground) of the vehicle. He was trapped that way for a while (hours?) and died later due to the damage to his cells from the current.

I can't attest to the validity of this story, but it sounds plausible as electric currents passing through chemicals can break down the molecules or form new ones.

13. ## Re: When does DC voltage become dangerous?

The problem with such a question is that the answer is so complicated. It's mostly the amount of current flowing into a vital organ that causes death.

If you run a current between two fingers on the same hand, only a small percent of the current will flow through, for instance, your heart. If you run the current from your left hand to your right hand, a larger percentage of the current will flow through the heart. A medical patient with, for instance electrodes for a heart monitor could have a much lower current threshold if there's some sort of electrical problem because .

Even though we say current is the problem, what we see most of the time is voltage. We are usually dealing with what we consider to be "constant voltage" sources. This would be something like a battery. It produces 1.5 Volts most of the time. If you have 0.01 mA flowing, it's 1.5 Volts. If you pull 500 mA out of it, it's still close to 1.5V.

Now, assume you have an exposed voltage of 50 V somewhere. If you walk up and touch it and have on shoes with rubber or plastic soles, the electrical resistance of your shoes is so high that you might only get a few micro amps. Change to leather soles, you still probably don't get much current. Now, assume you're touching a metal piece of furniture with one hand and touch the 50V circuit with the other. You get considerably more current. Now, consider if you have sweaty hands and are making really good contact with a grounded metal table. Now, assume you're standing in a decorative fountain with wet hands working on the water pump and you don't realize that the 50V DC power supply isn't turned off.

The threshold of "safe" voltage varies widely in these different situations because the electrical resistance varies so widely.

In the electrical engineer safety discussions, a "nightmare" scenario was something like "A technician is working on a piece of low voltage electronic equipment. The equipment has energized components with sharp edges, for instance voltage test pins. The technician slips and manages to spear a finger on each hand with a pin and pierce the skin. What's a safe voltage level here?" The answer was that there probably was no safe level.

With all that said, you mostly worry about voltages above 50V. You understand that lower voltages can still be dangerous in certain conditions. You become more concerned in wet conditions, or any kind of medical situation. Me, I start getting nervous above 12V, and ratchet up the nervousness as voltage gets higher.

You also understand that a lower voltage high current situation can cause thermal burn problems. For instance, shorting out a car battery with your class ring can cause a really nasty burn.

By the way, telephone wiring is around 48 Volts when the phone is on the hook, and we normally don't worry about that too much. However, if you're messing with some phone line connection and thoughtlessly decide to hold the connector in your mouth to free both hands, it can be an unpleasant or even fatal surprise. Especially if the phone rings, when the voltage jumps to around 90V.

14. ## Re: When does DC voltage become dangerous?

Originally Posted by BatteryCharger
Ok, theoretically in the right place you could probably be killed with 1ma @ 1v. More realistically speaking, when does DC voltage become dangerous to touch with your bare hands? 36v? 48? 75? How high does it need to be before you should be afraid of it like 120v sockets?

Just curious...
Ever get a little static shock? It's about 10,000 volts DC. Volts aren't the issue.

15. I've definitely gotten a charge out of this thread, which has sparked several observations.

Resistance is futile.
Protect the family Joules.
Stay current to maximize your potential.
Watts your problem? More power to you!

Oy -- Thank God it's Faraday.
(I know, I know -- revolting!)

16. ## Re: When does DC voltage become dangerous?

Just wondering, if I'd touch + and - of, let's say, 1000V DC with two of fingers on same hand, would the damage be limited to hand, or current will in some way go through whole body?
Sorry if this has been asked here, just too much posts to check all of them.

17. ## Re: When does DC voltage become dangerous?

99% of the time, you will only lose those fingers and the meat in between... but that 1% is still there looking to kill you. so basically, don't go around touching 1000v DC or AC systems unless you really don't value your life.

18. ## Re: When does DC voltage become dangerous?

My first electronics class instructor once said all it takes is 30V and 1/10th of an amp to kill you.

Doesn't seem like much with flashlight batteries that can put out 30A pulses these days.

I realize we're talking DC, but I had an uncle who was sorta famous for being able to hold onto the wires from a 120V AC wall outlet, although I don't think he was taking it across the chest, but I never witnessed it myself.

19. ## Re: When does DC voltage become dangerous?

Originally Posted by flashflood
I've definitely gotten a charge out of this thread, which has sparked several observations.

Resistance is futile.
Protect the family Joules.
Stay current to maximize your potential.
Watts your problem? More power to you!

Oy -- Thank God it's Faraday.
(I know, I know -- revolting!)
I appoint you to be in charge of the daily humor.
Balancing your d(humor)/dt will be a daily delicate balancing act.
I know you can do it, as long as you don't get overcharged.

20. ## Re: When does DC voltage become dangerous?

The most damage would be done where the current leaves your body. You need to isolate yourself from any ground. Use isolated tools. People in my line of work die from -48V unfused power. One guy was sweaty and bald bent down to get his wrench was touching a bus and his head hit the frame(which is bonded to ground). That room still smells funky and I get the chills when I work in there.

Amperage is what does the damage.

Voltage is just the pressure behind the current. Voltage needs to be high enough and your body's resistance needs to be low enough for the current to flow through you. Without any amperage though it is just like a static shock from the carpet. High voltage but harmless. Just fun to tease the cat.

21. ## Re: When does DC voltage become dangerous?

To add a theoretical example to Mr Happy's post. Lets say you had an old 350 Cubic Inch V-8 Chevy engine. A few decades ago, the starter motors for these engines pulled about 220 Amps at 12 Volts - OR 2,640 Watts of power were used to accomplish the work of turning over the engine if the starter was in good shape. Fairly thick cables are needed to move 220 Amps of current. IIRC something like #1's or aut or 2/0. In theory, (lots of other complications would occur) if you could find a 24 volt starter for that same engine, the starter would pull only 110 Amps at 24 Volts but you still are using the same 2,640 Watts of power (24 x's 110 = 2,640 Watts) to accomplish the same work. So higher voltage allows you to move less current while maintaining the same power level. Saves a lot of copper!

I wouldn't say that "Amperage is what does the damage". How many times have we touched a leaking 40KV spark plug wire only to quickly pull your arm away and have your elbow strike something and hurt like heck, if not draw blood.

22. ## Re: When does DC voltage become dangerous?

Back at school they taught me that from 40V, DC voltage can become deadly.

23. ## Re: When does DC voltage become dangerous?

http://www.darwinawards.com/darwin/darwin1999-50.html

anything 9v and over is potentially lethal in the right circumstances

24. Originally Posted by InHisName
I appoint you to be in charge of the daily humor.
Balancing your d(humor)/dt will be a daily delicate balancing act.
I know you can do it, as long as you don't get overcharged.
I am honored by this induction.

25. ## Re: When does DC voltage become dangerous?

Originally Posted by BVH
I wouldn't say that "Amperage is what does the damage". How many times have we touched a leaking 40KV spark plug wire only to quickly pull your arm away and have your elbow strike something and hurt like heck, if not draw blood.
The current itself did no damage, it was your nerves reacting causing the reflex. If that had been a 200 amp you'd lost your arm.

I stand by my statement that amperage is what does the damage, but yes you need enough voltage to overcome your resistance and complete the circuit.

Current = Voltage / resistance. I can't find what the average resistance of a human is though. I'm sure there would be variation among people and individuals sweaty and not etc. But if your resistance is higher than the voltage than current= Zero and there is no circuit. Wikipedia... electric shock

A person can feel at least 1 mA (rms) of AC at 60 Hz, while at least 5 mA for DC. The current may, if it is high enough, cause tissue damage or fibrillation which leads to cardiac arrest. 60 mA of AC (rms, 60 Hz) or 300–500 mA of DC can cause fibrillation.[2][3]

Body resistance

The voltage necessary for electrocution depends on the current through the body and the duration of the current. Ohm's law states that the current drawn depends on the resistance of the body. The resistance of human skin varies from person to person and fluctuates between different times of day. The NIOSH states "Under dry conditions, the resistance offered by the human body may be as high as 100,000 Ohms. Wet or broken skin may drop the body's resistance to 1,000 Ohms," adding that "high-voltage electrical energy quickly breaks down human skin, reducing the human body's resistance to 500 Ohms."[9]
The International Electrotechnical Commission gives the following values for the total body impedance of a hand to hand circuit for dry skin, large contact areas, 50 Hz AC currents (the columns contain the distribution of the impedance in the population percentile; for example at 100 V 50% of the population had an impedance of 1875Ω or less):[1
0]

End Quote

conductors/fuses are rated for amperage not by voltage or wattage.

Voltage is rated by the insulating properties of the sheath.

I always like the water analogy. For lower resistance and more current you need bigger ID pipes or wires. If you want to push the water/electricity further you need higher PSI/voltage and thicker walls on your pipe/wire. Over simplified but I still like it.
You need enough voltage to get the amperage to pass through your body for the amps to be dangerous

26. ## Re: When does DC voltage become dangerous?

In my youth, I accidentally took 12kv 30mA thru my hands. Scared the ever loving hell outta me. Left a bruise on my chest the size of a soft ball and 2 cauterized holes, one on each hand. I lived...... Idk how close to not living I was tho.

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28. ## Re: When does DC voltage become dangerous?

Originally Posted by SemiMan
In general things get "dangerous" at 30V wet, 60V dry.

Fritz, you were probably pretty lucky, but you would not be the first to get hit with something in that order .... like old TV flybacks, etc.

It's not just current (or the voltage needed to generate that current given contact points, skin surface resistance, etc.) but what happens w.r.t. your heart. Usually it's extended contact stopping the heart and a significant jolt stopping the heart that causes electrocution. I used to work with electricians that said 277/347 was scarier than 480/600V at times, because 480/600V would seriously hurt .... likely when it threw you across the room. On the other hand, touch 277/347 and it is hard to let go. Often when you do touch something "high voltage", the muscle contractions are severe enough to "throw" you away from the contact. If you happened to "grab" it though, then likely you are toast, as you may not be able to open your hand.

I am often working around 277VAC, and 500VDC, but in a lab environment. Isolation transformers are a great tool ... rubber gloves too ... and Crocs.
That's exactly what I was. Lucky.

Was a NST. The juice went right thru the insulation into my pointer finger on my right hand and into my left palm. Still have the scars.
Scariest thing was I couldn't let go. Was juiced for approx 10-15s..... Until I could get up enough.... "mental energy" to throw the wires down and at which point I literally jumped across the room, sweating and panting. Unplugged the NST, wrapped the cord around it and put it in the basement until I found a buyer for it. Lol
I've long since learned.

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30. ## Re: When does DC voltage become dangerous?

Originally Posted by SemiMan
Was that a new neon sign transformer or one of the newer (past 20 years) electronic ones. The new ones are high frequency which ends up being not as dangerous.

Old magnetic ones are quite dangerous.
It was one of the really old, iron core, tar potted, ceramic terminal units that breaks several bones if you ever dropped it on your foot.

I have a few of the newer ones, they have a spark gap that triggers a safety system so are almost useless for Jacob's ladders and the like.
I also have some of the old iron core as well.... Now that I know more about the safety aspects.

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