just got electrocuted, curious why it didn't seriously hurt

[iandy4]

Hi everybody,
I was just playing my guitar and decided to look something up on my laptop at the same time.  Bad idea.  

When my finger touched the click pad (which is metal and I assume grounded) I felt a hell of a buzzing sensation going through my finger.  I instantly remembered what R.G. told me about how differences in voltages of each devices ground network can cause hum so I decided to get out the multimeter and check what voltage I was shocked with.  It was the full 120 volts.  I had always thought that voltage was what caused pain but this wasn't too bad so am I right to assume it is amperage which is responsible for the pain or a combination of the two?

I then tried to check the amperage going between the guitar strings and the laptops click pad but didn't get a reading.  I suppose that is because it is somehow like putting the MM in parallel with the grounds rather than series (which I was told is necessary to get amperage readings)?

Also I had thought that big voltage differences between the grounds of my amp + guitar and my laptop couldn't be because they were plugged into the same wall outlet.  I learn something new everyday.

I'd appreciate any input on the matter.  I suppose you could say it's life or death  

[iq01221]

That's why I don't like laptops

[MikeH]

I'm confused- what did you touch?  Laptops usually run at around 24 volts DC from a wall wart supply, not the full 120 AC.

When I'm demoing I play guitar and touch my laptop at the same time a lot.  Never been shocked.  Certainly never been electrocuted - because that would mean I was killed with electricity.  

[iandy4]

I'm confused- what did you touch?  Laptops usually run at around 24 volts DC from a wall wart supply, not the full 120 AC.

When I'm demoing I play guitar a touch my laptop at the same time a lot.  Never been shocked.  Certainly never been electrocuted - because that would mean I was killed with electricity.  

My mistake.  I was mildly shocked.  I was touching my guitars strings (plugged into an amp which was connected to the same outlet as the laptop) with one hand and touched my laptops click pad (laptop embedded mouse) with the other.  I got a mild shock and then went to measure it, expecting a few volts.  The multimeter clearly showed 120vac.  I know its weird but that's why I asked.

[iandy4]

oh yea, and my laptops adapter is 19VDC

[patrickcurran21]

I hate it when that happens. I never thought much about it though... just figured it was the cosmic middle finger rearing it's head again...

[R.G.]

You didn't get a more severe shock because the current was limited.

The perceived severity of the shock is dependent on the amount of current that flows. The voltage is just a measurement of how much pressure is behind the current. Just like a huge pressure can force lots of water through a small opening, large voltages can make current flow through a high resistance. Static electricity on carpets in the winter time is thousands of volts, but such a small current that it's harmless. Lightning is just static electricity, but millions of amperes. Same cause, different current.

That's the academic side of it. You're lucky that you didn't in fact get killed. If that were my setup, I would be doing some serious (and very, very careful!) poking with that meter with one lead on the safety ground of the AC power line to find out which of the two things are "hot". Could be both, or it could be one or both outlets.

[Seven64]

same thing happens if you and a buddy are playing guitar and you touch the strings on both guitars at the same time.

[Seven64]

same thing happens if you and a buddy are playing guitar and you touch the strings on both guitars at the same time.

only on acoustic guitars tho

[theundeadelvis]

same thing happens if you and a buddy are playing guitar and you touch the strings on both guitars at the same time.

only on acoustic guitars tho

Don't you both have to be doing the devil horns sign with one hand too?

[greaser_au]

I have seen gear with switchmode supplies do this, the mains connection is 'capacitively coupled' across to the output side due to poor SMPS design allowing a very small current to flow. The only answer is that everything needs to be properly grounded, here's a couple of examples:

I used to work as a tech in a large amusements arcade chain. At one of our bigger centres, in the middle of the big room,  groups of machines were powered from industrial IP67 power outlets in the floor, using consumer grade power boards/strips.  One day I had a complaint that someone got a shock when they were leaning on one machine playing another - turns out the 2 machines  involved were on different outlets & one  power board was not plugged into the floor oulet properly - the ground pin was not connecting. the control panels (which are grounded normally) on all machines in that group were at 100V (measured on my meter).  Pushing the plug fully home (and instructing the centre manager on avoiding side entry plugs in those outlets) resolved the problem.

A few of years ago I had a batch of microATX machines with 2-pin mains cords, these were capable of delivering mild shocks also - the supplier made good by shipping us replacement PSUs with 3- pin mains connections.

R.G has already given sound advice. To add to that I'd suggest  making sure your laptop  power supply has a suitable 3-pin mains cable (and a 3-pin mains inlet) (gut feeling suggests we have a 2-pin mains cable involved here).

david

[Jazznoise]

It really is the lack of current that made that non fatal. Death due to electrocution usualy involves a sustained voltage where the victim cannot move due to the motor nerves spasming or a temporary one with a very high current. P = V x I. So if the current had been 1 amp and the volts 100 you'd have had 300 Watts of power burning out the delicate little wires that make up your body.  Humans are quite susceptible to this due to our high internal resistance, P = I^2 R.

Things like static electricity can generate huge Voltages, well into the thousdan volt range and up, but due to it being maybe a few thousand misplaced electrons the flow is too small and too short to do any damage. However they CAN be enough to wreck components , however, which is why you ground yourself before opening an appliace or computer. Some people do it before touching IC's, PIC chips or Trannies too. But some of us like to live dangerously 

[DougH]

One other thing: You didn't get "electrocuted" you got "shocked". If you had been "electrocuted" you wouldn't have been around to start this thread.

[MikeH]

But can someone explain where this 120v AC is coming from on a laptop that runs on 19v DC?

[iandy4]

Thanks for your input guys.

Found the problem!  I was poking around with the multimeter and it was obvious after a few seconds.  I had two power strips plugged into the same outlet.  The one power strip with the amp and guitar on it had 3 prong outputs but only a 2 prong input to the wall outlet.  The laptop was plugged into the other power strip which went to the same outlet but had a proper 3 prong input to the wall outlet.  When testing the 2 prong power strip I was getting strange voltage readings like 50vac between the ground prong and the smaller slotted prong and 1.2vac between the ground prong and the bigger slotted prong. The wall outlet that it was plugged into gave the expected reading of 123vac between the ground prong and the smaller slotted prong and zero-ish vac between the ground prong and the bigger slotted prong.

I'm still a little confused because I was going over the wiring of the house with my dad.  He showed me that each circuit in the house has a black, white and bare copper wire.  The copper is ground, the black is going to the smaller slotted prong and the white is going to the bigger slotted prong for each wall outlet in the house.  He showed me that at the circuit breaker the white and ground connect to the same neutral buss bar and that the black connects to one of the 120vac lines coming in from the power lines outside.  If this is the correct wiring it makes sense to me that appliances can have either 2 prong or 3 prong plugs because one of the two slotted prong is eventually connecting to ground.  The question it raises is, if the house is wired correctly, what is the point of having three prong outlets?

The relationship between amperage and voltage and why it hurts is clear now (should have just thought about ohms law) but I still don't really understand why I was shocked.  It was a difference in voltage between the grounds of the amp+guitar and laptop because in this case the amp wasn't properly grounded?

[iandy4]

One other thing: You didn't get "electrocuted" you got "shocked". If you had been "electrocuted" you wouldn't have been around to start this thread.

That was sorted out right in the beginning of this thread.  My apologies.

[iandy4]

But can someone explain where this 120v AC is coming from on a laptop that runs on 19v DC?

I bet R.G. can explain this.  I think it has to do with the amp not being properly grounded.  That could explain why there was the full 120vac difference between the "grounds" because the amp was not actually grounded.  I don't know if that's it but hopefully R.G. will chime in again and clarify.

[theundeadelvis]

But can someone explain where this 120v AC is coming from on a laptop that runs on 19v DC?

I bet R.G. can explain this.  I think it has to do with the amp not being properly grounded.  That could explain why there was the full 120vac difference between the "grounds" because the amp was not actually grounded.  I don't know if that's it but hopefully R.G. will chime in again and clarify.

My assumption, by the description of your setup, is that the laptop was not providing 120 volts, the amp was. The laptop was merely in the path of the better ground. Which means you may be lucky some of the more sensitive components of the laptop weren't fried too.

[wavley]

But can someone explain where this 120v AC is coming from on a laptop that runs on 19v DC?

I bet R.G. can explain this.  I think it has to do with the amp not being properly grounded.  That could explain why there was the full 120vac difference between the "grounds" because the amp was not actually grounded.  I don't know if that's it but hopefully R.G. will chime in again and clarify.

I would imagine this is because your amp was not properly grounded and your laptop acted as ground.

This is why your gear should always be grounded on the same circuit as anything else you may come in contact with.  I know that it isn't always easy to do in cases of playing out live and such, but it's worth it to not get a shock.  There's that old guitar player trick of touching your guitar strings to the mic to see if there's a spark and then flipping the ground switch on the amp if it does (still not safe by the way, but better than finding out with your lips)

[iandy4]

If you don't have the possibility to change the wiring, which might be the case in a live situation, would running a wire between the mics metal housing and the amps chassis solve the problem?  I would guess that if the electricity is trying to find the path of least resistance, the wire is going between the mic and the guitar strings with you then you are pretty much a big resistor in parallel with the added wire which is pretty much no resistance so the current would opt to flow throw the wire.  Is this the correct way to think about it?

I'm asking because my friend says he is getting shocked all the time while playing in his basement.  I haven't been able to see how they have their set up and I'd like to be able to solve the problem.