List of reasons why AC power is dangerous

I would like to make a list of things that can go wrong when messing with AC power (as in 240V@16A or 120V@15A). And suggestions on how to avoid these dangers.

I will start with what I have heard. (Please correct me if I'm wrong on any of these.)
I'd also like to back the claims up if possible, e.g. by linking a study or news story etc. or speak from your own experience. I'd appreciate any help on this as well.

  • Touching the phase may cause ventricular fibrillation which you can die from. (Although it seems unlikely, considering how many people I know who have survived it unharmed. Are there any studies on how likely this is?)
    Possible counter measures:
    • Make sure there is a residual-current device installed in your breaker box.
    • Turn off the fuse of the circuit you're working on (in the breaker box).
    • Use of insulated gloves, insulated boots, mats and tools.
  • If a wire is too thin or is not making enough contact, it could cause it to heat up to the point that it starts a fire. (Keep in mind that the insulation of your wires can melt, causing them to short with other wires.)
    Possible counter measures:
    • Use wires with a gauge that can handle your current
    • Learn how to solder properly / Screw the wires into the screw terminal deep enough
    • Use wires with a silicone insulation (the insulation is much more heat resistant)
    • Put more fuses in your circuits that prevent more current from flowing than what your components and wires can handle safely
  • If your house burns down and the insurance finds that it was your fault (they are better at this than you'd think), you'll have to pay for the damage and may even go to jail if people died in the process. (Obviously, this doesn't apply to all countries, but be aware of your local laws.)
    Possible counter measures:
    • Hire a professional electrician to do it for you or to approve what you have done.
    • Get a good lawyer.
    • Buy flame retardant to make your things resistant to catching on fire. (For example your curtains.)
  • If your AC circuit is too close to your DC circuit, the AC may randomly (voltage spikes) jump (spark gap) over into your DC circuit causing it to die and maybe even cause a fire. So keep in mind that the circuit you made 3 years ago that has never had any issues, may catch on fire the next time there is a random voltage spike.
    Possible counter measures:
    • I heard that galvanic isolation is supposed to help with that, but I have no clue if that is true.
    • You might also want to consider using an overvoltage protection device. Ideally directly in your breaker box, but you can also get ones that you put between an outlet and your device.

I will update this list with your suggestions.

I'm not trying to scare anyone away from messing with AC power, but I'm also not encouraging anyone in doing so. This is merely for educational purposes.

Can be used to kill rogue elephants.

Easy there, Edison.
Save it for old sparky.

The "rumor is" higher voltage will sometimes completely stop your heart and then it will re-start OK (similar to a defibrillator, I guess). But people struck by lightning sometimes have permanent muscular or neurological damage, if they survive. (Hmmm... I wonder what the odds are of surviving a direct lightning strike...)

I've survived 120VAC a few times. More than once I've changed a light switch or power outlet without turning-off the power (because I'm lazy and I'd have to reset clocks, etc.). And a few times wasn't careful enough... The last time I did this, I didn't get shocked but a wire came loose, sorted-out, made a spark, and blew the breaker anyway.

I don't remember ever getting shocked by 240V, but here in the U.S. we have "split phase" so there is only 120V between hot & ground (or neutral) and it's not as easy to get 240V across your body. I've been shocked by 300VDC in tube amplifier (a long time ago) and the worst shock I ever got was from a spark plug on a lawn mower...

What actually kills you is current (Ohm's Law says Current = Voltage/Resistance.) From what I remember, 1 Amp is lethal. At low voltages the high resistance of your body means you won't get dangerous current. (Somebody once showed me how to test a 9V battery by touching both terminals to your tongue... Under some conditions you can "feel" 9V.)

So the resistance of your body is a factor, as well as the voltage. If you are wet or standing in a puddle or water (or in the bathtub) and you get "good contact" with the wire or other energized object, things can get very bad.

Of course it has to be capable of supplying enough voltage to kill or hurt you. You'll see experiments/demonstrations with Tesla coils, etc., where a spark is hitting someone. There isn't enough current through the body to hurt the person so the voltage drop across the body is relatively low with most of the voltage drop being through the air (in the spark).

Generally, anything over 50V is considered dangerous. If you are selling a product and the consumer can touch a 48V power supply or battery, that's OK. But over 50V and it has to be insulated/isolated.

It also depends on the current-path. Current through your finger and thumb is unlikely to kill you. Current through your heart or brain is more dangerous.

Turn off the power!!! :wink:
Electricians wear insulated shoes.
People who work on high voltage (higher than power-line voltage) also usually put one hand in their pocket so there no current-path through their body. (That's not practical for electricians.)

When I was in high school my mother said she was getting a "tingle" from the waffle iron. I didn't feel anything but I was wearing sneakers. I knew a little about electricity so I knew it might be my sneakers, but I really thought my mom was feeling "something else". So I touched the waffle iron and then reached-over and briefly touched the water faucet with my finger. BLAM... BIG JOLT through my chest. Obviously, I'm still alive but it was scary. And I said, "Boy, that was stupid!" And, I advised my mom to get a new waffle iron and I think she did.

That's just another way of saying "electrical isolation". If there is no electrical-contact there is no current path, you are safe. But although a transformer is electrically-isolated, a transformer with dangerous voltages on the secondary is still dangerous. An "isolation" transformer (i.e. with 120V on the primary and secondary) provides some protection because there is no current path between the secondary and earth ground... You can safely touch one leg of the secondary and ground at the same time, and no current will flow through your body and you won't feel anything, but still not recommended!

1 Like

Last night I was messing with a 4kV plasma ball power supply (I had a hand behind my back, I'm not that dumb). I noticed that my arm started feeling a bit weird, so I grounded myself. There wasn't a shock, so I figured I was fine and continued. About a minute later, I realized that electricity was indeed flowing properly and coming out the wire I was holding (making arcs and noise), but it was also coming THROUGH THE INSULATION and arcing to my right hand.

If I had touched the plasma ball's PCB with my other hand while it was on, it would have killed me.

Morals of the story (there's a few):

  1. Put a hand behind your back when working with high voltage.
  2. Use sufficient insulation.
  3. When using high voltage, everything is a wire. Including you. Be careful.
1 Like

And don't forget the air.

1 Like

Better see few of his videos --> ELECTROBOOM! He can give you a very good example of how dangerous electricity can be...


1 Like

I love that idiot


DC is much more dangerous than AC. It is a bad idea to rectify the AC without a good reason. (Once I have considered to rectify and filter a 2kW heater to reduce its hum. Now I believe it was a very stupid idea.)

1 Like

Edison had another opinion: [url][/url]

Edison was not a dispassionate observer.

National Electric Code (U.S.) defines high voltage is anything above 70V.

I've read that as well. Apparently with DC your muscles lock making it difficult for you to move away from the electrode.

In my experience they both seem very similar.

If you have to ask, then don't try it.

Three ways electricity can kill

What's that?

No voltage but current is killing peoples.

Under normal conditions, the resistance of the human body is assumed to be approximately 1 kΩ. The flow of alternating current of more than 50 mA begins to cause irreversible damage to the human body. Therefore, from Ohm's law it follows that the "safe" voltage value is: 1 kΩ · 50 mA = 50 V. Therefore, AC residual current devices (the most popular) are designed to switch off the circuit in the event of exceeding half the rated current value differential (most often equal to 30 mA) - it guarantees the appropriate sensitivity of the device and at the same time effectively protects the human being.


Fall occurs when you recoil from the shock of electric current

(even when the amount of voltage/current may not be enough for electrocution)

This is why linemen must know how to apply CPR while up on a power pole.