Grounding: You NEED To Watch This Video

[Paul Marossy]

Watch this video, it will shock you - no pun intended. (Audio Noise And Grounding, right hand side)

http://www.taylorguitars.com/videos/?id=52&tab=ss&pg=1

[theundeadelvis]

A very good illustration of something more people should be aware of.

[deadastronaut]

cool vid ...yep ive had shocks off mics at various gigs.......nasty....

[Paul Marossy]

cool vid ...yep ive had shocks off mics at various gigs.......nasty....

Happened to me once, too - on an outdoor gig running on a generator!

Kind of scary when you can have a 60V AC differential between the ground of the PA and the string ground on your guitar. 

[guitarbobby]

wouldn't the fuse to the amp/microphone's PA/shop fuse box just blow if the current started flowing between the mic and his teeth?

I was about to buy a second hand amp from a friend once, until he told me that it kept blowing fuses and that he put a piece of wire where the fuse goes.

[mth5044]

Very good information, and really easy to understand. I was given one of those voltage pens for Christmas last year.. cool to know that they aren't just novel pieces of junk

I was about to buy a second hand amp from a friend once, until he told me that it kept blowing fuses and that he put a piece of wire where the fuse goes.

[petemoore]

wouldn't the fuse to the amp/microphone's PA/shop fuse box just blow if the current started flowing between the mic and his teeth?
  Which one ? Just not me.
  Just a super-nasty shock is the good news, the other good news is everything is on a ground [desert show caveats].
  Very demonstrative of the LVDetector, nice little gadget !
  I was about to buy a second hand amp from a friend once, until he told me that it kept blowing fuses and that he put a piece of wire where the fuse goes.
  There's a reason for that, and it's reason enough to suggest it as price consideration.
  The only thing worried me is ''the world is a safe place'' [after he said 10 times 'very/dangerous situation']. It is safe if you make your grounds, certainly.
  Buy gear that has 3prong AC cable, at both ends.
  Read
   http://geofex.com/Article_Folders/Power-supplies/powersup.htm

  Some linear supplies only need the IEC connector installed [with super secure ground/Lug/chassis connection, wedged tightly in place].
  Others amps have no PT, so a quick ground fix isn't possible...not designed for connecting to humans or modern equipment.
 

[R.G.]

wouldn't the fuse to the amp/microphone's PA/shop fuse box just blow if the current started flowing between the mic and his teeth?

Very definitively not.

Fuses are rated to NOT blow until the current through them is bigger than their rating. A 1A fuse will NOT blow until the current through it is more than 1A for some period of time. Fuses only know the current that's flowing through them, and how much it is. They can't tell that the current's going where it isn't supposed to.

Nor will a 3A or bigger fuse, common for guitar amps and PAs, protect you. it takes about 20ma of line frequency current through your chest to send your heart into an irrecoverable fibrillation, and you die unless someone has a heart-shocker setup handy. The fuse would not even notice this small an amount of additional current.

[FlyingZ]

A common cause of hum is feedback voltage on the ground.

[Renegadrian]

it takes about 20ma of line frequency current through your chest to send your heart into an irrecoverable fibrillation, and you die unless someone has a heart-shocker setup handy.

[guitarbobby]

so what are the fuses for? I've seen someone touch a live wire (by accident) and all that happened was he said he felt a big electirc shock, and the fuse box for the house went, and the switch just had to be reset (i.e. all the electrics to the house were cut off, lights, fridge, etc) im also ashamed to say that years ago (junior school ago) I innocently put a knife into a toaster to get a piece of bread out! again the house elcetrics went out and I didnt feel an electric shock at all (but I was scolded no end)

did the guy in the video disconnect the earth pin? because i thought that (UK) plugs worked in such a way that the earth pin goes in first, and releases the flaps for the live and neutral pins to go in. if there is no earth pin, tthe flaps stay shut and there is no circuit. but what do i know

also, pretty much every gig I have played, no matter how small, if it is public, things like plug sockets have to be PAT safety tested. once I even had to buy about 8 of the 9v batteries just to run my pedal board because the power adapter hadnt been tested, and the techies refused to let me use it!

[Quackzed]

i have a peavey special 150 amp with a ground switch on the front panel, + on one side, O in middle position,and - on the other side.
my fender head also has an a,off,b ground switch...
does that mean that in the middle position, of each, that it is lifting ground?
i usually keep em both alone peavey on - and fender on A ...
or is this somehow a safe way to ground lift inside the amp, as opposed to running it without the 3rd prong? or something different?
should i pay close attention to these switch settings to avoid a dangerous shock?!? or are they somehow isolated safely ?
i always use a proper plug, and generally a surge protector as well...

[petemoore]

  Without the 3rd prong, the chassis isn't grounded.
 With a solidly wired safety ground, greater happiness and greatly reduced chance of tragedy can be guaranteed.

[Paul Marossy]

Fuses are rated to NOT blow until the current through them is bigger than their rating. A 1A fuse will NOT blow until the current through it is more than 1A for some period of time. Fuses only know the current that's flowing through them, and how much it is. They can't tell that the current's going where it isn't supposed to.

Nor will a 3A or bigger fuse, common for guitar amps and PAs, protect you. it takes about 20ma of line frequency current through your chest to send your heart into an irrecoverable fibrillation, and you die unless someone has a heart-shocker setup handy. The fuse would not even notice this small an amount of additional current.

Does that apply for a fast acting type, too? I know that amps use the slow blow types so the inrush current doesn't blow them. It's scary how small an amount of current can actually kill you, in the right set of circumstances - 20mA is not much current at all.

 Without the 3rd prong, the chassis isn't grounded.
 With a solidly wired safety ground, greater happiness and greatly reduced chance of tragedy can be guaranteed.

Yeah, that and the ground is now "floating" on that piece of equipment. That creates a voltage potential between grounds like you see in that video. It's interesting that what people think is helping with noise by defeating the ground is actually making matters far worse as far as noise is concerned.

so what are the fuses for? I've seen someone touch a live wire (by accident) and all that happened was he said he felt a big electirc shock, and the fuse box for the house went, and the switch just had to be reset (i.e. all the electrics to the house were cut off, lights, fridge, etc)

The fuse is often there for the equipment's sake, to keep it from getting damaged. In your friend's case, the circuit breaker did its job and protected him from potentially being electrocuted to death. He became the path to ground and made the breaker trip. It sounds like that circuit breaker he tripped might have been tied to the GFCI circuit in the electrical panel (if there is one, it's been required for something like the last 20 years).

[dmc777]

That particular video doesn't show up for me. It shows the title and all but no video. Anyone else having this problem? I'm on a Mac which could be the issue.

[Paul Marossy]

That particular video doesn't show up for me. It shows the title and all but no video. Anyone else having this problem? I'm on a Mac which could be the issue.

Might be the problem. Here is a direct link to the YouTube video: http://www.youtube.com/watch?v=6ZGokkrsO_Y

[mohn]

Even if your amp is properly grounded, you may run into trouble with differing grounds among outlets at a gig or even your friendly practice space.  I discovered this the hard way, when, while practicing in a garage, the other guitarist's (uncut  ) string brushed my arm, sending me a nice shock.  We were both using 3-prong, properly grounded amps.   However, we were not plugged into the same outlet, and the difference in ground potential for each outlet was enough to feel!  So, if you have a meter with you, simply testing the voltage between your strings and the other player's strings should give a good indication of proper outlet grounding. 

[Paul Marossy]

Even if your amp is properly grounded, you may run into trouble with differing grounds among outlets at a gig or even your friendly practice space.  I discovered this the hard way, when, while practicing in a garage, the other guitarist's (uncut  ) string brushed my arm, sending me a nice shock.  We were both using 3-prong, properly grounded amps.   However, we were not plugged into the same outlet, and the difference in ground potential for each outlet was enough to feel!  So, if you have a meter with you, simply testing the voltage between your strings and the other player's strings should give a good indication of proper outlet grounding. 

Yeah, you can't be too safe when it comes to this sort of thing. What I found really interesting in that video was when he disconnected the amp from ground and everything had AC coupling going on - the mic cable, the guitar cable, the guitar. I really didn't know that there was all that going on when you have a piece of equipment not grounded (I have never defeated the grounds on any piece of equipment). I mean I know that there is some AC coupling going on all the time because we are surrounded by AC in our world, but that little low voltage detector really made things very obvious. Kind of a fascinating phenomenon.

[Slade]

I needed to see it, and my friends too, thanks for posting it.

[yeeshkul]

http://www.youtube.com/watch?v=4YM1iwC6vhg&feature=related

He talks about ground loops here. First he gets rid of the loop noise by disconnecting one of the amps, and hurray the noise is gone. The he lifts the ground of one of the amps, and for some reason the noise is back, which he describes like the noise is the way ... er we expected. Right after that he advises that we should use well grounded amps. A bit confusing video.