Dude, NOT COOL! (electric shocks/sparks)

[jay4321]

Question for experienced electricity/wiring types...

So I'm sitting on in my office, strat plugged in to the amp. Jamming a little bit and all is well. Cell phone rings, I grab it, and as I get up the loose guitar strings I didn't cut come in contact with a metal lamp. I didn't really feel anything, but it sent a shower of sparks about when those errant string ends hit the lamp.

The lamp and the amp are plugged into the same outlet. The amp has that three-prong power plug which I assume means it's grounded. The lamp does not. I have never had a problem with either, though I do have a dead outlet in the room and one other in the house. I also have the electrical know-how of a doorknob.

Can anyone here briefly explain what this could be? A faulty amp? An electrical issue in my house? Bad outlet? I'd appreciate seasoned responses as guesswork could go badly for me. I also appreciate in advance anyone who would like to suggest I call an electrician--I will do so through my condo management as that's their end of it. In the meantime hoping someone could maybe educate me on what might be going on, as I live here and am too young to die/quit guitar playing.

 

[Dan025]

hmmn. that is odd to happen with a lamp. cb and others know more about the amp side of things and why the voltage at the guitar might be other than neutral so i'll leave that alone. this is odd, ac electricity in a residence in the US usually has two hot leads in opposing phase and a neutral the is tied to ground before the breaker. the two hots make up the 220 volt circuits that run washing machines and such and the neutral is used in conjunction with one hot for the 110v circuits, the box spreads it out so half the circuits are on one hot and half on the other. an ac appliance doesn't care which is hot and which is ground, it is not about true voltage of each but the voltage difference and in ac the current alternates direction. grounds are added to devices for safety, if a hot conductor comes in contact with the outer case a short circuit is created and the breaker should trip. if a neutral fails the ground will prevent any component the the user is exposed to from becoming hot.

now in theory the lamp should be insulated as the neutral is not a substitute for a ground, if the neutral fails in the cord or the prong breaks on the plug or there is some resistance or loss of continuity any where then voltage will go through hot into the bulb and out the other end into the neutral and anything connected to it. in the case that there was a short between the neutral and a metal part of the lamp then you would not notice unless there was an additional problem with the neutral, you would not feel anything. if the lamp is very old or made by some know it all type the neutral might be being used as a "ground" by design. i have seen many old designs that use grounds as neutrals for contactor controls or neutrals as grounds but it is poor and unsafe practice and against fire code in some states now.

it is also possible that one of those loose strings made it's way into the area where the bulb screws in. if the lamp is insulated and the plug on the end can go in to the outlet either way then the hot can be on either the threaded portion of the bulb or the contact at the end of the bulb. if the string came in contact with the hot it would certainly throw some sparks.

if you have non functional outlets you should probably have it checked out, it is likely a tripped or faulty breaker but you safety is too important to ignore it. the electrician may look for 30 seconds and be like that's it or you might be in for some major updating and repairs but would you rather wonder every day if the house is gonna burn down or if you are prone to electricution?

 

[mayfly]

Two possbilities:

1 - the insulation of the hot lead of the lamp has worn through and now the hot lead is touching the lamp's metal casing.  That's 120V on the outside of the lamp.

2 - You've got an old amp with a "death cap" and/or a signal ground that's not tied to chassis ground.


Here's how you determine what's what.

Get an ohm meter and check the resistance between the guitar and the third prong of the amp.  If it's zero, then the problem is the lamp.

I would not be touching that lamp when plugged in if it were me.

 

[ironeddie]

it sounds like that would have been a funny video on youtube.  Sorry about your bad luck though...

 

[jay4321]

Get an ohm meter and check the resistance between the guitar and the third prong of the amp.  If it's zero, then the problem is the lamp.

I would not be touching that lamp when plugged in if it were me.

Well the lamp (and really, the amp) are both cheap and expendable. I do need an ohm meter anyway, that sounds like a good place to start thanks

 

[TroubledTreble]

Glad you did not get hurt!

Once you have a meter, plug in the guitar, turn on the amp, put the meter on the volt scale starting with the highest scale, then (carefully) touch one lead to the strings and the other lead to the lamp and see if you have a voltage potential. It will be interesting to see what type of reading you get.

I will try this myself once I'm near my amp. I am curious to see if there is any voltage leak.

One issue with lamps is that with a two wire cord the lamp stem or housing is not grounded. If for some reason the amps ground is bad then the lamp may have become the shortest distance (or least resistance) to ground even though the lamp housing is not grounded with a wire but touching the ground through contact with the floor. Most likely the amp has a poor ground. Definately worth looking into.

BTW does your amp even have a 3 wire cord? If not put one on and ground the transformers housing.

 

[-CB-]

Two possbilities:

1 - the insulation of the hot lead of the lamp has worn through and now the hot lead is touching the lamp's metal casing.  That's 120V on the outside of the lamp.

2 - You've got an old amp with a "death cap" and/or a signal ground that's not tied to chassis ground.


Here's how you determine what's what.

Get an ohm meter and check the resistance between the guitar and the third prong of the amp.  If it's zero, then the problem is the lamp.



I would not be touching that lamp when plugged in if it were me.

Dollars to donuts the lamp is wired wrong, and the 120 is touching the metal case.  Being a lamp, it works either way.  Fix the lamp.  The death cap thing is more rumor and innuendo than fact.  In all my dealings with amps... from about age 14 to 53.... which is a decent amount I venture to say, I've never once ever seen or heard of any real problem due to the "death cap" syndrome.  I have seen absolutely crap stage wiring, reverse phased wiring, all sorts of wiring issues... and these have resulted in 120v potential from say... mic to lips to fingers to strings.... but that is not a matter of death cap, but a matter of reverse phase and crap wiring.  Any good stage setup - in fact any LEGAL stage setup, should have ONE source of power, one only, and it should be run into center stage or center back stage where everything can be certified as being correctly in phase.  Its even worse... far worse.... on "real stage" setups, aka, high schools auditoriums (and even worse... gyms), church stages etc.  At that point, you've got a 3phase wye setup.  In a 3phase wye, you get two real decent 120v phases, and one 208v single phase.  They can run decent motor loads from that - AC, ventilation, curtain hoists, other stage motors, and still have two real powerful lighting loads of 120v.  Get those puppies back to back, you can damn near weld your lip to the ball on a Shure mic.

Take a good look at the lamp...