Strings Shocking Me

[jnewman]

So, when my guitar (stock Fender Stratocaster) is plugged into my amplifier (Stock Marshall JTM60 Combo), **whether the amp is turned on or not**, and I am playing barefoot in my room (which has a flagstone floor), my strings shock me a little bit. This also happens if I unplug the guitar and just touch the ground/tip of the cord while it is plugged into the amp. It doesn't happen if I'm wearing shoes or have my feet sitting on a book or clothes or something. It's not strong enough to zap on my fingertips, but on the backs of my hands, or my arms, it zaps pretty good. With my feet on the ground, I get a reading of about 30V DC between my skin and the strings and about 60V AC between my skin and the strings.

Until I made this measurement, I thought I was maybe just getting a ground loop or something, myself grounded at a different level from the amp. Now that I find that there's AC voltage as well, it seems obvious there is some kind of serious problem. I've unplugged the amp and won't be playing it until I get this resolved.

The amplifier sounds just fine, although it has been making a few popping sounds recently (I had assumed it was just because the tubes are getting old).

Is one of the transformer taps shorting into the ground channel? Is a tube blown? Can anyone tell me what's going on?

Thanks,

Jimmy

EDIT: Forgot to add. None of the tubes LOOK blown. There are four little Ruby's and two big Groove Tubes, I can't read what types through the screen that's protecting them.

Edited April 14, 2005 by jnewman

[GregP]

I don't know how to solve your problem and I don't have any technical information, but I do know this: I have an old 50-Watt Garnett head. There's a switch on the back for reversing the current or whatever... dunno exactly what's going on, but if it's flipped one way, all's good, but when it's flipped the other, very nasty electric shocking occurs. I wonder if somehow at the amp level or in the outlet it's plugged into, something is 'reversed' the same way that switch reverses things.

Greg

[borge]

i get shocks off my warlock

but that was something to do with the gat coz it doesnt happen on my rg on the same amp

[lovekraft]

It sounds like the outlet you're plugged into is miswired - you really need to correct it immediately, it's a potentially fatal scenario. Do not use the setup any further until the amp and the outlet have been checked by a qualified technician!

[jnewman]

Thanks for the heads-up. It is indeed a problem outlet, for some reason the ground (third actual ground pin, not the relative neutral pin) is running right at 60V AC halfway in between the neutral pin and 120V hot pin. I know better and should have checked that to begin with, but it didn't occur to me.

It's very strange, because I'm living in a college dorm and we have commercial-grade wiring and this has only started happening in the last week or two. At least it's only the one outlet and not the whole power system.

I'll buy an extension cord today to cover the stuff plugged in there (there are only three outlets in the room) and talk to the maintenance guys about getting it fixed.

[crafty]

Yeah, my old dorm room had some pretty messed up wiring, too. The lesson here is to purchase a cheap outlet tester so you can check the outlets wherever you go. I played at a 50 year old church a couple months ago that had only one good outlet, and it was 30 feet from where I needed to place my amp!

I also run EMGs now, so the strings are pretty much isolated from the ground potential, but that wouldn't make the cable, panels, jacks, and knobs on my amp any safer.

[sepultura999]

i'm guessing your amp has a 3 prong plug, and your amp, pedals, etc, are being used in the same outlet.

I'm told that should help, but also do what lovekraft suggests.

Do you get outlet testers at any local hardware store?

-Jamie

[thedoctor]

Contact the maint. people in charge of your dorm. You have a VERY serious problem that could hurt people running hairdryers, irons, hotplates (I know, don't tell) or anything else using the three-prong grounded cord. Most commercial builings use 208 VAC 3-phase as their incoming power to eliminate transformers for lighting and when a neutral comes loose in this wiring configuration. grounds become conductors and 120 volt outlets can put out over 200 volts, under the right circumstances. Bad deal!!! Could just be that one outlet, also.

[GuitarGuy]

Contact the maint. people in charge of your dorm. You have a VERY serious problem that could hurt people running hairdryers, irons, hotplates (I know, don't tell) or anything else using the three-prong grounded cord. Most commercial builings use 208 VAC 3-phase as their incoming power to eliminate transformers for lighting and when a neutral comes loose in this wiring configuration. grounds become conductors and 120 volt outlets can put out over 200 volts, under the right circumstances. Bad deal!!! Could just be that one outlet, also.

←

You could use a fused power bar. That could pervent serious injury in the interm.

[Maiden69]

If you are haviing a reading of 60Vac at the ground there is something that is messed up that it's plugged into the wall. If the wiring is wrong you will either have no reading or 120.

[thedoctor]

Sorry, maiden, that is not correct in a polyphase circuit. If a load other that the one you are applying to the neutral circuit is not getting a good connection, the remaining current can show up as 1 to 220 volts at your outlet. It has to find a return path somewhere and it isn't always 100% of the total applied voltage. They burn up tools at construction sites all the time by getting loose-neutral "added voltage" to their extension cords, GFI or not.

[Gorecki]

i'm guessing your amp has a 3 prong plug, and your amp, pedals, etc, are being used in the same outlet.

I'm told that should help, but also do what lovekraft suggests.

Do you get outlet testers at any local hardware store?

-Jamie

←

Yes, these are what I use before ever plugging my gear into anything. Keep one in my shop and one in a case for travel.

[Paul Marossy]

Do you happen to know if you have single or three phase wiring in your building?

[crafty]

I use a little Tripp-Lite combo outlet tester and surge protector that came with my laptop a few years ago. It'll test the outlet for good wiring and it doesn't seem to inject any noise into the power line. You can purchase regular little testers for next to nothing at most hardware stores, though.

BTW, most dorms built after the '40s have three-phase because of elevators, air handlers, and the extreme power consumption of such a large occupied building.

[jnewman]

It is just the one outlet that is having the problem, I've checked all the outlets in my room. The amp does have a third pin. The third pin (in the outlet, not on the amp) reads 60VAC with nothing at all plugged in to the outlet. I am not sure whether or not the building is on three-phase, although it was built in the early 70's.

I do intend to make sure it gets fixed.

[lovekraft]

You could use a fused power bar. That could pervent serious injury in the interm.

Don't rely on a fuse to protect you from electrocution - that assumes that the fuse will blow before your heart does, and in practice the opposite is too often true. A fuse is great protection from over-current that can result in fires and other damage, but it only takes about 40 milliamps to kill you if it's routed through your chest. Gorecki's got the right idea - it takes maybe 10 seconds to check an outlet, but you're dead forever.

[Gorecki]

I learned very early!

I'll tell ya a little story from when I was about 6 years old. My uncle Johnny had a Horse/Cow/Bull farm. Well to keep the bulls contained they used a high voltage electric fence. I being a little kid was often instructed when on a farm if you gotta 'GO', just go to a bush and 'GO'. Well running along this bush is the electric fence....all I remember is KAHBOOM (least that's what it felt like), knocked me out cold and woke up laying on the floor inside the house having no idea where I was.

Moral of the story, make sure your wall plugs are ground correctly....AND DON'T PEE ON AN ELECTRIC FENCE!

[Maiden69]

poly phase you mean like 220 and 230-430 3 phase, on the 220 or the 3phase you can, but on 120, thatls all the line is bringing into the house, and it can't be splitted to 60, unless you aree in Europe and that's the way over there, but if I'm noyt wrong the ES system is regulated and it runs on single phase 110-220 (which 220 is a 2 phase but electricians still call it single phase) or comercial tri-phase that is 115-230-460 depending on how you wire it.

At least that was all I learned, and worked with!

[thedoctor]

Nope. Houses built after the 50s have poly-phase. Two available phases for power and double the voltage using BOTH phases. Commercial three-phase comes in 4 varieties( 208, 230/240/440/480). The only ones in use for, say a dormatory, are 208, which requires no transformer for 120VAC single-phase, like lights and 440 that DOES require a transformer to run 120 volt stuff. Industrial 3-phase is usually 240 VAC that has a "high or dog leg" and 440 that has a balanced ABC load capability but no 120 VAC available without proper transforming. 480 is a grounded-leg 3-phase used only for heavy motor-load and such industrial applications. Dorms are usually built with 208 three phase cause it saves a bunch on wiring and is hard to make mistakes with. All three phases are 120 VAC to neutral. No "high" leg to worry about and no transformer needed. More than you wanted to know but I blab a lot.

[Paul Marossy]

This whole thing is kind of strange to me. I was initially thinking that maybe one leg of a 3-phase panel was whacked or something. Maybe the three legs in the local sub-panel were recently somehow made really imbalanced?

[Maiden69]

Actualy not more than I wanted to know, since I use to work installing comercial gate openers. And most were the 230-460 (which I think that its the 220-440 you mention) We just call them by the rating on the actual opener, but the poly phase that you mention is the same as the 110-220 that I say (If I ain't mistaken) When I went to college they called it single phase, and i use to disscuss with the prof that why was it called single when there were actualy 2 live wires, he got mad at me and usualy walked away. But i still can't understand why the "poly" phase as you call it will yield 60 volts is both phases are 110? I know this because I have wired a few rooms in my grands house, that was wired for the pre 50's 2 prong outlets.

I have never seen an outlet puting out 60Vac, since any way you ground a live wire will read 110, I did had one that was reading 85Vac, but it was a wire that got the insulation peeled away while the electritian snake it thru the conduit, and in humid days it will short but no enough to trip the braker, we found out, because Isteped on the area while cleaning the garage barefoot and felt the floor warm and a slight tinglin sensation. This is why I think there is a messed up wire or something that is draining the voltage to ground.

[crafty]

What do you want to bet that some jackass in the dorm drove a nail in the wall and hit a wire?

[thedoctor]

Here we go. Poly-phase means just that. More than one phase. In a modern house, two "hot" lines and a neutral come in from the transformer on the pole or slab outside the house. Each HOT has 120vac potential to neutral. That individual potential is single-phase; a sine wave that goes above and below neutral 120 vac (lets not get into RMS here). Between the two HOTS you have a potential of 240vac because the sine waves are 180 degrees apart or "in opposition" to each other. One is above neutral while one is below. At this point I shall clarify the difference between neutral and ground. Anyone who has wired a load center or fuse box in a house knows that ground and neutral are bolted together or "bonded" by law. The difference is that a neutral is SUPPOSED to conduct current all the time power is being used in a single-phase application. The ground is NEVER supposed to conduct current! It is there for safety and zero-reference (shielding) ONLY!

NOW, 3-phase is about 4 other beasts. In 208 vac three-phase the three phases are 120 degrees apart from each other with 115 vac potential from each of the three hots to neutral. That makes three available single-phase circuits available for use as lighting, wall outlets, etc. NO WILD-LEG, HIGH-LEG, DOG-LEG or whatever you want to call it. 115 vac from any hot to neutral. That is why commercial buildings like hotels and dorms love it. 208 vac is available from ANY two hot legs.

Then you got 240 3-phase. 120vac single-phase is available from TWO of the hots to neutral and the other hot leg is called "high leg" "wild leg" etc. Any two hots give 240 vac between them.

I really don't see the point in going into 460 3-phase and 480 3-phase but I will if asked. Is that long-winded enough for you? It is for me!

[Paul Marossy]

Reading that great explanation of the different types of voltages and phases by thedoctor, this 60V thing is even more enigmatic to me now!

EDIT: OK, dumb question time. In 120VAC 1-phase, since there are two hots and a neutral, what is the purpose of the ground? I know it's for safety, but why couldn't one just use the neutral as a ground? (Sorry, I'm not an electrician... )

Edited April 15, 2005 by Paul Marossy

[thedoctor]

No, Paul, one hot and a neutral. SINGLE-phase The stray 60 (who came up with that?) or 200 or 45 volts comes from a loose or compromised NEUTRAL. A load down the line or even the cirduit being questioned has a problem getting the current to go back through the correct neutral path because of a loose wirenut or some such and it shows up as wierd, not-expected voltage at the outlet. Case in point. My late father-in-law had a rewired 1930's row-house in Chicago that the lights whould get BRIGHTER instead of dimmer when the airconditioner kicked on. The loose neutral (in this case at the pole-mounted xfmr) it put the leg of single-phase the lights were using at a "higher-than-neutral" potential because of a loose connection out at the pole. I argued and ranted and raved until the power company sent a guy out who sat at the pole and watched the neutral float from 20 volts below to 90 volts above neutral while I turned crap on and off in the house. If the neutral is not conducting back to the source, as it should, you can get any volatage up to the available incoming, anywhere. Spent most of my life fixing this kind of crap and I STILL ain't seen it all. Clear as mud, ain't it?